Reviewed on: SoundStage! Solo, June 2019
I measured the Monoprice 24459 using a Clio 10 FW audio analyzer and a Neutrik NL-1 Minilyzer. I measured only the unbalanced output; for some reason I couldn’t figure out, the amp always went into protection mode when I connected the balanced output into a load resistor. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality.
This chart shows the Monolith 24459’s frequency response with 1mW output into a 32-ohm load using the coaxial digital input. (Measurements with 250- and 600-ohm loads produced effectively identical results.) With the Normal digital-to-analog (DAC) filter, response measured -0.057dB at 20Hz, -0.227dB at 20kHz, and -1.470dB at 40kHz. With the Slow1 filter, the numbers were -0.057dB, -0.307dB, and -6.007dB, respectively. With the Slow2 filter, the numbers were -0.060dB, -0.975dB, and -4.307dB, respectively. These measurements were taken with a 192kHz digital signal, which the coax input accepts, but the digital circuitry is brick-wall filtered at about 40kHz (consistent with Monoprice’s published frequency response), so the effective resolution is actually 96kHz. Note the +1.2dB ringing of the Normal filter at 37kHz. From a technical standpoint, this isn’t impressive, but it won’t be audible. The ringing nearly disappears with the Slow1 and Slow2 filters.
This chart shows the effect of the two different analog-to-digital converter’s filter settings on the frequency response. Both were measured with 1mW output into a 32-ohm load using the unbalanced analog input, with the DAC filter set to Normal. (Measurements with 250- and 600-ohm loads produced effectively identical results.) With the Normal analog-to-digital (ADC) filter, response measured -0.057dB at 20Hz, -0.067dB at 10kHz, and -0.344dB at 30kHz. With the Slow1 filter, the numbers were -0.010dB, -0.139dB, and -0.922dB, respectively. Thus, the difference between the two filters might be just barely audible. (I cite the response here at 10kHz and 30kHz instead of my usual 20kHz and 40kHz because of the slightly non-smooth characteristics of the response curves.)
This chart shows the unbalanced output of the Monoprice 24459 vs. total harmonic distortion (THD) into 32-, 250-, and 600-ohm loads. Note that Monoprice’s power ratings are specified at 16, 32, 150, 300, and 600 ohms, so some of my measurements are not directly comparable. Output into 32 ohms was 1420mW at 0.5% THD and 1475mW at 1% THD. Output into 250 ohms was 183mW at 0.5% THD and 190mW at 1% THD. Output into 600 ohms was 77mW at 0.5% THD and 79mW at 1% THD. (Monoprice’s ratings are 1360mW into 32 ohms, 150mW into 300 ohms, and 73mW into 600 ohms, all with THD unspecified). These are very high numbers for a headphone amp, indicating that the Monolith 24459 should have no problem driving any headphones currently available.
Here you can see the harmonic distortion spectrum and noise floor of the Monolith 24459, referenced to 6.295Vrms (1.24W) output at 600Hz into 32 ohms. (I used this odd output number as a reference because, as best I can tell, the amplifier stage just barely starts to distort before the unit’s analog-to-digital converter stage clips. Any higher and the distortion becomes very high; any lower and there’s not enough distortion to see the harmonic content.) Harmonic distortion is predominantly odd-order, which is much more audible than even-order distortion, but with the 3rd harmonic at -78.2dBFS and the 5th harmonic at -79.4dBFS (both just slightly over 0.01% distortion), and the distortion occurring only at an extremely high output level, I think the chances of any listener actually hearing this are zero. Note also that the noise floor was generally at about -120dBFS. This is excellent performance.
I measured the output impedance of the unbalanced headphone jack at less than 0.5 ohm, which is as low as I could measure without triggering the amp’s protection circuit. In my opinion, an output impedance of less than 1 ohm is a good standard for headphone amps because it prevents the headphone amp from significantly interacting with the headphones’ impedance in a way that alters the headphones’ frequency response.
. . . Brent Butterworth
brentb@soundstagenetwork.com
Reviewed on: SoundStage! Solo, April 2019
I measured the Schiit Audio Fulla 2 using a Clio 10 FW audio analyzer and a Neutrik NL-1 Minilyzer. I used the Fulla 2’s analog input for all these measurements, because I haven’t yet found a way to get digital test signals from the Clio 10 FW to USB DACs. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality.
This chart shows the Fulla 2’s frequency response with 1mW output into 32-ohm and 600-ohm loads. (Frequency response at 250 ohms is not shown because it almost perfectly overlapped with the response at 32 ohms.) Into 32 ohms, the response measures -0.011dB at 20Hz, -0.031dB at 20kHz, and -0.085dB at 75kHz. Into 600 ohms, the numbers are -0.009dB, -0.044dB, and -0.186dB, respectively. These are excellent results, comparable to those of a good high-end analog preamp.
This chart shows the output of the Fulla 2 vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads. Note that Schiit’s power ratings are specified at 16, 50, 300, and 600 ohms, so some of my measurements are not directly comparable. Output into 32 ohms is 320mW at 0.5% THD and 340mW at 1% THD (Schiit’s rating is 360mW into 32 ohms, THD unspecified). Output into 250 ohms is 50mW at 0.5% THD and 51mW at 1% THD. Output into 600 ohms is 21mW at 0.5% THD and 22mW at 1% THD. These numbers are all very impressive for a $99 DAC-headphone amp.
Here you can see the harmonic distortion spectrum and noise floor of the Fulla 2, referenced to 1V RMS output at 600Hz into 32 ohms. Distortion is very low, with the second harmonic slightly higher in level than the third; I’d say this would make the Fulla 2 sound “tubey” if the distortion at this output level and load were high enough for you to hear, but that second harmonic is at -79dB. You can also see that the noise floor of the amp is way down around -110dB.
I measured output impedance of the headphone jack at 3.2 ohms at 1kHz; Schiit rates it at 0.5 ohm. Note that this measurement, made with a potentiometer used as a voltage divider, is not super-accurate, and any output impedance in the low single digits is low enough not to react significantly with the reactance of the headphones, and thus won’t change their frequency response.
. . . Brent Butterworth
brentb@soundstagenetwork.com
Reviewed on: SoundStage! Solo, January 2019
I measured the iFi Audio xCAN using a Clio 10 FW audio analyzer and a Neutrik NL-1 Minilyzer. Except as noted, I used the xCAN’s unbalanced analog input and unbalanced analog output, because I don’t yet have an adapter for 2.5mm balanced outputs I can use for measurements. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality, and that gauge the efficacy of any special features and functions that might be measurable.
This chart shows the xCAN’s frequency response with all processing off, and with XBass II engaged in its three different modes (Bass, Presence, and Bass+Presence), with 1mW output into a 32-ohm load. With processing off, the response measures -0.14dB at 20Hz and -0.19dB at 20kHz. Bass mode boosts response by 9.96dB at 20Hz. Presence mode boosts response in a 4.12dB peak centered at 1288Hz. Frequency response did not change in 3D+ mode, and also did not change with 250-ohm and 600-ohm loads.
This chart shows the unbalanced output of the xCAN vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads. Note that iFi’s power ratings are specified at 16, 50, 300 and 600 ohms, so some of my measurements are not directly comparable. Output into 32 ohms is 320mW at 0.5% THD and 336mW at 1% THD (iFi’s rating, in S-balanced/unbalanced mode, is 380mW into 32 ohms, THD unspecified). Output into 250 ohms is 46mW at 0.5% THD and 49mW at 1% THD. Output into 600 ohms is 20mW at 0.5% THD and 19mW at 1% THD.
Here you can see the harmonic distortion spectrum and noise floor of the xCAN, referenced to 3Vrms output at 600Hz into 32 ohms. The third harmonic at 1.8kHz is slightly more predominant than the second harmonic, which will sound a little more objectionable than an amp (like a typical tube amp) with predominantly second-harmonic distortion, but if you actually dare to listen at 3Vrms (280mW into 32 ohms), the distortion from the headphones will likely be far louder than the distortion from the amp.
I measured the unbalanced output impedance at 1.2 ohms at 1kHz; iFi rates impedance at <2 ohms for balanced and <1 ohm for unbalanced output. Regardless, the output impedance is low enough not to react significantly with the reactance of the headphones, and thus won’t change their frequency response.
. . . Brent Butterworth
brentb@soundstagenetwork.com
Reviewed on: SoundStage! Solo, October 2018
I measured the iFi Audio xDSD using a Clio 10 FW audio analyzer and a Neutrik NL-1 Minilyzer. For all of these tests, I used the xDSD’s coaxial digital input. Note that this is the first DAC-headphone amp I’ve measured for SoundStage! Solo; I’ve decided to focus my efforts on tests that confirm such devices’ basic functionality, and that gauge the efficacy of any special features and functions that might be measurable.
This chart shows the xDSD’s frequency response in its Listen and Measure modes, and with XBass+ engaged, with a 24-bit/192kHz S/PDIF signal and the xDSD set for 1mW output into a 32-ohm load. The response in both modes measured -0.16dB at 20Hz and -0.26dB at 20kHz. Listen mode actually measured slightly better here, with less rolloff above 65kHz; apparently, the switch is mislabeled. The bass boost in XBass+ mode was 6.48dB at 20Hz.
This chart shows the xDSD’s frequency response in Listen and Measure modes, and with XBass+ engaged, with a 16/48 S/PDIF signal and the xDSD set for 1mW output into a 32-ohm load. The treble response at 20kHz in Measure mode is -1.91dB, and in Listen mode -0.32dB. Definitely, the switch is mislabeled. According to the xDSD manual, the Listen filter is “transient-optimized minimum phase” and the Measure filter is “frequency response optimized,” but a filter with -1.91dB rolloff at 20kHz is certainly not “frequency response optimized.”
This chart shows the output of the xDSD vs. its total harmonic distortion (THD) into loads of 32, 250, and 600 ohms. Although iFi specifies the xDSD’s power output into 16, 50, 300, and 600 ohms, which renders most of my measurements not directly comparable, those measurements do suggest that iFi’s specs are on the mark. The xDSD’s output into 32 ohms is 291mW at 0.5% THD and 304mW at 1% THD; into 250 ohms, the output is 53mW at 0.5% THD and 54mW at 1% THD; and into 600 ohms, the xDSD puts out 22mW at 0.5% THD and 23mW at 1% THD.
Here you can see the xDSD’s spectrum of harmonic distortion and noise floor when driven by a 24/192 S/PDIF signal and referenced to 1.5V RMS output at 600Hz. Note that the distortion profile of the Measure and Listen modes is effectively the same.
I measured the xDSD’s output impedance as 0.8 ohm at 1kHz, which confirms iFi’s rating of <1 ohm. I prefer a headphone amp’s output impedance to be 1 ohm or less; the output impedance will then not react significantly with the reactance of the headphones, and thus won’t affect the ’phones’ frequency response.
. . . Brent Butterworth
brentb@soundstagenetwork.com
Link: reviewed by Dennis Burger on SoundStage! Access on May 1, 2024
General Information
All measurements taken using an Audio Precision APx555 B Series analyzer.
The Marantz Model 50 was conditioned for one hour at 1/8th full rated power (~9W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.
The Model 50 offers four line-level analog inputs (RCA), one moving-magnet (MM) phono input (RCA), a sub output and left/right variable and fixed pre-outs plus a power amp input (all RCA), two pairs (A and B) of speaker-level outputs, and one headphone output over 1/4" TRS connector. For the purposes of these measurements, the following inputs were evaluated: analog line-level and phono.
Most measurements were made with a 2Vrms line-level analog input and a 5mVrms phono input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 70W (8 ohms). For comparison, SNR measurements were also made with the volume at maximum.
Based on the variability and non-repeatability of the left/right volume channel matching (see table below), the Model 50 volume control is digitally controlled operating in the analog domain. The Model 50 overall volume range is from -57.6dB to +41.8dB (line-level input, speaker output). It offers 0.5dB increments throughout the volume range.
Our typical input bandwidth filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs. frequency sweeps, where a bandwidth of 10Hz –90kHz was used. Frequency response measurements utilized a DC to 1MHz input bandwidth.
Volume-control accuracy (measured at speaker outputs): left-right channel tracking
Volume position | Channel deviation |
-99.5 | 0.062dB |
-80 | 0.065dB |
-70 | 0.088dB |
-50 | 0.082dB |
-30 | 0.081dB |
-20 | 0.081dB |
-10 | 0.066dB |
0 | 0.046dB |
Published specifications vs. our primary measurements
The table below summarizes the measurements published by Marantz for the Model 50 compared directly against our own. The published specifications are sourced from Marantz’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 1MHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.
Parameter | Manufacturer | SoundStage! Lab |
Amplifier rated output power into 8 ohms (1% THD+N, unweighted) | 70W | 83W |
Amplifier rated output power into 4 ohms (1% THD+N, unweighted) | 100W | 132W |
THD (1kHz, 10W, 8ohms) | 0.02% | 0.005% |
Frequency response (line-level) | 5Hz-100kHz | 5Hz-100kHz (-0.1/-0.2dB) |
Damping factor | 100 | 188 |
Input impedance (line level) | 16k ohms | 21.7k ohms |
Input impedance (phono) | 47k ohms | 50.5k ohms |
Input impedance (power amp in) | 15k ohms | 17.7k ohms |
Input sensitivity (line level, RCA, maximum volume for 70W) | 185mVrms | 193mVrms |
Input sensitivity (phono, maximum volume for 70W) | 1.4mVrms | 1.45mVrms |
Input sensitivity (power amp in, for 70W) | 1.5Vrms | 1.53Vrms |
SNR (line-level, 70W, 2Vrms in, A-weighted) | 116dB | 109dB |
SNR (phono, 70W, 5mVrms in, A-weighted) | 87dB | 87.4dB |
SNR (power amp in, 70W, A-weighted) | 125dB | 125.4dB |
Tone controls | ±10dB at 50Hz/15kHz | ±10dB at 30Hz/20kHz |
Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Maximum output power into 8 ohms (1% THD+N, unweighted) | 83W | 83W |
Maximum output power into 4 ohms (1% THD+N, unweighted) | 132W | 132W |
Maximum burst output power (IHF, 8 ohms) | 91.4W | 91.4W |
Maximum burst output power (IHF, 4 ohms) | 143.2W | 143.2W |
Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |
Crosstalk, one channel driven (10kHz) | -75.4dB | -76.6dB |
Damping factor | 190 | 188 |
Clipping no-load output voltage | 30.4Vrms | 30.4Vrms |
DC offset | <-8mV | <9mV |
Gain (pre-out) | 17.9dB | 17.8dB |
Gain (power amp) | 23.8dB | 23.8dB |
Gain (maximum volume) | 41.8dB | 41.7dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-85dB | <-88dB |
IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-75dB | <-78dB |
Input impedance (line input, RCA) | 21.7k ohms | 21.7k ohms |
Input impedance (power amp in, RCA) | 17.7k ohms | 17.7k ohms |
Input sensitivity (70W 8 ohms, maximum volume) | 193 mVrms | 194 mVrms |
Noise level (with signal, A-weighted) | <40uVms | <41uVms |
Noise level (with signal, 20Hz to 20kHz) | <54uVms | <55uVms |
Noise level (no signal, A-weighted, volume min) | <22uVms | <22uVms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <28uVms | <28uVms |
Output Impedance (pre-out) | 546 ohms | 544 ohms |
Output Impedance (sub-out, 20Hz) | 692 ohms | |
Signal-to-noise ratio (70W 8 ohms, A-weighted, 2Vrms in) | 108.5dB | 108.7dB |
Signal-to-noise ratio (70W 8 ohms, 20Hz to 20kHz, 2Vrms in) | 106.6dB | 106.6dB |
Signal-to-noise ratio (70W 8 ohms, A-weighted, max volume) | 88.4dB | 88.4dB |
THD ratio (unweighted) | <0.005% | <0.004% |
THD+N ratio (A-weighted) | <0.0057% | <0.0044% |
THD+N ratio (unweighted) | <0.005% | <0.004% |
Minimum observed line AC voltage | 123 VAC | 123 VAC |
For the continuous dynamic power test, the Model 50 was able to sustain 145W into 4 ohms (~3.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (14.5W) for 5 secondss, for 233 seconds of the 500-second test before inducing the fault-protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the Model 50 was warm to the touch.
Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz sinewave at 5mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Crosstalk, one channel driven (10kHz) | -75.0dB | -77.6dB |
DC offset | <-8mV | <8mV |
Gain (default phono preamplifier) | 42.4dB | 42.5dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-87dB | <-876dB |
IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-90dB | <-90dB |
Input impedance | 50.4k ohms | 50.5k ohms |
Input sensitivity (to 70W with max volume) | 1.45mVrms | 1.45mVrms |
Noise level (with signal, A-weighted) | <400uVrms | <430uVrms |
Noise level (with signal, 20Hz to 20kHz) | <950uVrms | <950uVrms |
Noise level (no signal, A-weighted, volume min) | <21uVrms | <22uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <27uVrms | <27uVrms |
Overload margin (relative 5mVrms input, 1kHz) | 22.6dB | 22.6dB |
Signal-to-noise ratio (70W, A-weighted, 5mVrms in) | 87.5dB | 87.4dB |
Signal-to-noise ratio (70W, 20Hz to 20kHz, 5mVrms in) | 82.2dB | 82.5dB |
Signal-to-noise ratio (70W, A-weighted, max volume) | 76.6dB | 76.3dB |
THD (unweighted) | <0.0020% | <0.0017% |
THD+N (A-weighted) | <0.0052% | <0.0052% |
THD+N (unweighted) | <0.012% | <0.012% |
Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left and right channels |
Maximum gain | 41.8dB |
Maximum output power into 600 ohms (1% THD) | 615mW |
Maximum output power into 300 ohms (1% THD) | 674mW |
Maximum output power into 32 ohms (1% THD) | 221mW |
Output impedance | 330 ohms |
Maximum output voltage (1% THD into 100k ohm load) | 29.7Vrms |
Noise level (with signal, A-weighted) | <14uVrms |
Noise level (with signal, 20Hz to 20kHz) | <19uVrms |
Noise level (no signal, A-weighted, volume min) | <10uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <13uVrms |
Signal-to-noise ratio (A-weighted, 1% THD, 14Vrms out) | 109dB |
Signal-to-noise ratio (20Hz - 20kHz, 1% THD, 14Vrms out) | 107dB |
THD ratio (unweighted) | <0.0047% |
THD+N ratio (A-weighted) | <0.0055% |
THD+N ratio (unweighted) | <0.0048% |
Frequency response (8-ohm loading, line-level input)
In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the Model 50 is essentially perfectly flat within the audioband (20Hz to 20kHz). At the extremes, the Model 50 is -0.1dB at 5Hz and -0.2dB at 100kHz. The Model 50 can be considered a high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.
Frequency response (8-ohm loading, line-level input, bass and treble controls)
Above is a frequency response (relative to 1kHz) plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/-11dB of gain/cut is available at 20Hz, and roughly +/-10dB of gain/cut at 20kHz.
Phase response (8-ohm loading, line-level input)
Above are the phase response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The Model 50 yields very little phase shift (as expected given the extended frequency response), with less than +5 degrees at 20Hz (the Model 50 is not DC coupled) and less than -5 degrees at 20kHz.
Frequency response (line-level pre and sub outputs)
Above is a frequency response plot measured at the line-level outputs into 8 ohms, where the left/right pre-outs are in purple/green and the sub-out is in blue. The pre-outs show an extended frequency response, -0.1dB at 5Hz and -0.5dB at 70kHz. The sub-out is low-pass filtered with a -3dB point at around 150Hz.
Frequency response (8-ohm loading, MM phono input)
The chart above shows the frequency response (relative to 1 kHz) for the phono input (MM configuration) and shows very small maximum deviations of about +0.25/-0.1dB (100-200Hz/20kHz) from 20Hz to 20kHz. What is shown in this chart is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB).
Phase response (MM input)
Above is the phase-response plot from 20Hz to 20kHz for the phono input, measured across the speakers outputs at 10W into 8 ohms. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and -90 degrees at 20kHz.
RMS level vs. frequency vs. load impedance (1W, left channel only)
The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .
. . . is the same but zoomed in to highlight differences. Here we see that the deviations between no load and 4 ohms are around 0.15dB. This is a reasonably strong result for an integrated class-AB amp, and an indication of a low output impedance, or high damping factor. With a real speaker load, deviations measured just below the 0.07dB level—well below the threshold of audibility.
THD ratio (unweighted) vs. frequency vs. output power
The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 70W. The power was varied using the Model 50 volume control. Between 20Hz and 2kHz, all THD ratios are fairly constant and similar, between 0.004 and 0.006%. Between 2kHz and 20kHz, THD ratios were higher at higher power levels, but not by a significant margin. At 20kHz, we measured around 0.01% at 1W and 10W, and 0.03% at 70W.
THD ratio (unweighted) vs. frequency at 10W (MM input)
The graph above shows THD ratio as a function of frequency plot for the phono input measured across an 8-ohm load at 10W. The input sweep was EQ’d with an inverted RIAA curve. The THD values vary from 0.01% (20Hz) down to between 0.001 and 0.002% from 200Hz to 3kHz, then up to 0.006% at 20kHz.
THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD ratios measured at the speaker-level outputs of the Model 50 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). THD ratios were essentially identical into 8 and 4 ohms up to the 8-ohm “knee” at roughly 70W (the 4-ohm “knee” is at roughly 100W). These ranged from 0.003% at 50mW, down to 0.001% at 1 to 3W, then up to 0.005% at the “knees.” The 1% THD values were hit at 83W and 132W into 8 and 4 ohms, respectively.
THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD+N ratios measured at the output of the Model 50 as a function of output power for the line level-input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track closely, but the 4-ohm data yielded a couple dB more noise than the 8-ohm data. THD+N ratios into 8 ohms ranged from 0.02% at 50mW, down to 0.002% at 10W, then up to just below 0.005% at the 8-ohm “knee.”
THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)
The chart above shows THD ratios measured at the output of the Model 50 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 20W at the output into 8 ohms (and roughly 40W into 4 ohms, and 80W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find essentially identical THD ratios (0.005%) into all three loads up to about 1kHz. From 3kHz to 20kHz, there is a roughly 5dB increase in THD between the 2-ohm load and the 8/4-ohm loads. At 20kHz, we measured 0.015% into 8/4 ohms, and 0.025% into 2 ohms. This is a strong result, and shows that the Model 50 is stable into 2 ohms.
THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows THD ratios measured at the output of the Model 50 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Generally, THD ratios into the real speakers were similar to the resistive dummy load, with the expection of the two-way speaker at 20 to 30Hz. THD ratios hovered between 0.007 and 0.01% from 40Hz to 20kHz for all three loads. At 20Hz, the THD ratio was 0.07% into the two-way speaker. This is a relatively strong result, and shows that the Model 50 will yield consistently low THD results into real-world speaker loads.
IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows intermodulation distortion (IMD) ratios measured at the output of the Model 50 as a function of frequency into an 8-ohm load and two different speakers, for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical IMD ratios into all three loads, at a relatively flat and constant 0.005%.
IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows IMD ratios measured at the output of the Model 50 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a thee-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical IMD ratios into all three loads, at a relatively flat 0.02% from 40Hz to 500Hz, then down to 0.0015% from 500Hz to 1kHz.
FFT spectrum – 1kHz (line-level input)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at -85dBrA, or 0.006%, and -105dBrA, or 0.0006%, while subsequent signal harmonics are below -110dBrA, or 0.0003%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak and its harmonics (120, 180, 240, 300Hz, etc.) at and below the very low -120dBrA, or 0.0001%, level.
FFT spectrum – 1kHz (MM phono input)
Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MM. We see the second (2kHz) signal harmonic dominate at -95dBrA, or 0.002%, while subsequent signal harmonics are below the -110dBrA, or 0.0003%, level. The noise related peaks are at and below the -85dBrA, or 0.006%, level.
FFT spectrum – 50Hz (line-level input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonics at a -90dBrA, or 0.003%, and -105dBrA, or 0.0006%. Noise related peaks can be seen below the -110dBRa, or 0.0003%, level.
FFT spectrum – 50Hz (MM phono input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input configured for MM. The most predominant (non-signal) peaks are that of the power-supply fundamental (60Hz) and third (180Hz) harmonics at -90dBrA, or 0.003%, and -85dBrA, or 0.006%. The signal’s second (100Hz) harmonic is at the -95dBrA, or 0.002%, level.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values were set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -95dBRa, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz are at -100dBrA, or 0.001%.
Intermodulation distortion FFT (line-level input, APx 32 tone)
Shown above is the FFT of the speaker-level output of the Model 50 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are at and below the very low -120dBrA, or 0.0001%, level.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MM. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBRa, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are at the same level.
Squarewave response (10kHz)
Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the Model 50’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Model 50’s extremely high bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, due to the Model 50’s very extended bandwidth, we see a near-perfect squarewave, with sharp corners and no ringing.
Damping factor vs. frequency (20Hz to 20kHz)
The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 200, from 20Hz to roughly 20kHz. This is a relatively strong damping factor result for an affordable class AB integrated amp.
Diego Estan
Electronics Measurement Specialist
Link: reviewed by George de Sa on SoundStage! Simplifi on May 1, 2024
General Information
All measurements taken using an Audio Precision APx555 B Series analyzer.
The Rotel RAS-5000 was conditioned for one hour at 1/8th full rated power (~17W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.
The RAS-5000 offers one pair of line-level analog inputs (RCA), a sub output (RCA), left/right pre-outs (RCA), one coaxial S/PDIF input (RCA), one optical S/PDIF input (TosLink), one USB digital input, a pair of speaker level outputs, and one headphone output over a 1/4" TRS connector. Bluetooth, streaming, and HDMI (eARC) inputs are also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level.
Most measurements were made with a 2Vrms line-level analog input and 0dBFS digital input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 140W (8 ohms). For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum.
Based on the variability and non-repeatability of the left/right volume channel matching (see table below), the RAS-5000 volume control is digitally controlled but operating in the analog domain. The RAS-5000 overall volume range is from -69dB to +32.4dB (line-level input, speaker output). It offers 1dB increments up to about the 75% mark, and then 0.5dB steps to full volume.
Our typical input bandwidth filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs. frequency sweeps where a bandwidth of 10Hz–90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.
Volume-control accuracy (measured at speaker outputs): left-right channel tracking
Volume position | Channel deviation |
min | 0.05dB |
10% | 0.074dB |
30% | 0.035dB |
50% | 0.041dB |
70% | 0.035dB |
90% | 0.005dB |
max | 0.017dB |
Published specifications vs. our primary measurements
The table below summarizes the measurements published by Rotel for the RAS-5000 compared directly against our own. The published specifications are sourced from Rotel’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 1MHz, assume, unless otherwise stated, 10W into 8ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.
Parameter | Manufacturer | SoundStage! Lab |
Amplifier rated output power into 8 ohms (1% THD+N, unweighted) | 140W | 154W |
Amplifier rated output power into 4 ohms (1% THD+N, unweighted) | 220W | *230W |
THD (1kHz, 10W, 8ohms) | <0.03% | <0.0014% |
IMD (60Hz:7kHz, 4:1) | <0.03% | <0.005% |
Frequency response (line-level) | 10Hz-100kHz (0, ±0.5dB) | 10Hz-100kHz (-0.2, +0.2dB) |
Frequency response (digital, 24/192) | 10Hz-70kHz (0, ±3dB) | 10Hz-70kHz (-0.2, -2.9dB) |
Damping factor (20Hz-20kHz, 8 ohms) | 290 | 314 |
Input sensitivity (line level, RCA, maximum volume for rated power) | 0.78Vrms | 0.806Vrms |
Input sensitivity (digital, maximum volume for rated power) | -8dBFS | -7.9dBFS |
Input overload (line level) | 4.1Vrms | 4.75Vrms |
Input impedance (line level, RCA) | 46k ohms | 53.2k ohms |
SNR (line-level, A-weighted) | 103dB | 114dB |
SNR (digital 24/96, A-weighted) | 105dB | 115dB |
Tone controls | ±10dB at 100Hz/10kHz | ±8dB at 100Hz/10kHz |
*protection circuit enabled after a few seconds
Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Maximum output power into 8 ohms (1% THD+N, unweighted) | 154W | 154W |
Maximum output power into 4 ohms (1% THD+N, unweighted) | *230W | *230W |
Maximum burst output power (IHF, 8 ohms) | 183.8W | 183.8W |
Maximum burst output power (IHF, 4 ohms) | 314.8W | 314.8W |
Continuous dynamic power test (5 minutes, both channels driven) | fail | fail |
Crosstalk, one channel driven (10kHz) | -61.6dB | -66.7dB |
Damping factor | 319 | 314 |
Clipping no-load output voltage | 43.3Vrms | 43.3Vrms |
DC offset | <-0.6mV | <-0.9mV |
Gain (pre-out) | 6.06dB | 6.05dB |
Gain (maximum volume) | 32.4dB | 32.4dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-92dB | <-93dB |
IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-88dB | <-86dB |
Input impedance (line input, RCA) | 51.9k ohms | 53.2k ohms |
Input sensitivity (140W 8 ohms, maximum volume) | 0.806Vrms | 0.806Vrms |
Noise level (with signal, A-weighted) | <62uVrms | <57uVrms |
Noise level (with signal, 20Hz to 20kHz) | <106uVrms | <80uVrms |
Noise level (no signal, A-weighted, volume min) | <50uVrms | <48uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <72uVrms | <62uVrms |
Output impedance (pre-out) | 223 ohms | 223 ohms |
Output impedance (sub-out) | 222 ohms | |
Signal-to-noise ratio (140W 8 ohms, A-weighted, 2Vrms in) | 114.1dB | 113.9dB |
Signal-to-noise ratio (140W 8 ohms, 20Hz to 20kHz, 2Vrms in) | 108.3dB | 109.2dB |
Signal-to-noise ratio (140W 8 ohms, A-weighted, max volume) | 107.7dB | 107.7dB |
Dynamic range (140W 8 ohms, A-weighted, digital 24/96) | 114.5dB | 114.9dB |
Dynamic range (140W 8 ohms, A-weighted, digital 16/44.1) | 95.1dB | 95.2dB |
THD ratio (unweighted) | <0.0014% | <0.0013% |
THD ratio (unweighted, digital 24/96) | <0.0014% | <0.0012% |
THD ratio (unweighted, digital 16/44.1) | <0.0015% | <0.0013% |
THD+N ratio (A-weighted) | <0.0019% | <0.0016% |
THD+N ratio (A-weighted, digital 24/96) | <0.0018% | <0.0016% |
THD+N ratio (A-weighted, digital 16/44.1) | <0.0024% | <0.0022% |
THD+N ratio (unweighted) | <0.0019% | <0.0016% |
Minimum observed line AC voltage | 123VAC | 123VAC |
*protection circuit enabled after a few seconds
For the continuous dynamic power test, the RAS-5000 was able to sustain 237W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (23.7W) for 5 seconds, for 233 seconds of the 500-second test before inducing the fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the RAS-5000 was warm to the touch.
Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left and right channels |
Maximum gain | 32.4dB |
Maximum output power into 600 ohms (1% THD) | 1.3W |
Maximum output power into 300 ohms (1% THD) | 1.4W |
Maximum output power into 32 ohms (1% THD) | 427mW |
Output impedance | 329 ohms |
Maximum output voltage (1% THD into 100k ohm load) | 43.3Vrms |
Noise level (with signal, A-weighted) | <27uVrms |
Noise level (with signal, 20Hz to 20kHz) | <40uVrms |
Noise level (no signal, A-weighted, volume min) | <27uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <40uVrms |
Signal-to-noise ratio (A-weighted, 1% THD, 20Vrms out) | 115dB |
Signal-to-noise ratio (20Hz - 20kHz, 1% THD, 20Vrms out) | 115dB |
THD ratio (unweighted) | <0.002% |
THD+N ratio (A-weighted) | <0.0027% |
THD+N ratio (unweighted) | <0.003% |
Frequency response (8-ohm loading, line-level input)
In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the RAS-5000 is essentially perfectly flat within the audioband (20Hz to 20kHz). There’s a +0.4dB rise in the frequency response at 200kHz, and -0.2dB at 10Hz. The RAS-5000 can be considered a high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.
Frequency response (8-ohm loading, line-level input, bass and treble controls)
Above is a frequency-response (relative to 1kHz) plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/-11dB of gain/cut is available at 20Hz, and roughly +/-9dB of gain/cut at 20kHz.
Phase response (8-ohm loading, line-level input)
Above are the phase-response plots from 20Hz to 20kHz for the line level input, measured across the speaker outputs at 10W into 8 ohms. The RAS-5000 yields very little phase shift (as expected given the extended frequency response), with +10 degrees at 20Hz (the RAS-5000 is not DC coupled), and less than -5 degrees at 20kHz.
Frequency response (line-level pre and sub outputs)
Above is a frequency response plot measured at the line-level outputs into 8 ohms, where the L/R pre-outs are in blue/red, and the sub-out is in purple. All three plots overlap perfectly, with a ruler-flat and extended frequency response, as was seen with the speaker outputs. The sub-out is not low-pass filtered in any way, and is likely simply a summed L/R version of the pre-outs.
Frequency response vs. input type (8-ohm loading, left channel only)
The chart above shows the RAS-5000’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency response graph above, but limited to 80kHz. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, all four plots yield the same -0.2dB at 10Hz. The -3dB points for the 16/44.1, 24/96, and 24/192 digital input data are: 21.0kHz, 35.1kHz, and 71.2kHz.
Digital linearity (16/44.1 and 24/96 data)
The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outputs of the RAS-5000, where 0dBFS was set to yield 2Vrms. The digital input was swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output was analyzed by the APx555. The ideal response would be a straight flat line at 0dB. The 16/44.1 data were essentially perfect as of -100dBFS down to 0dBFS, while the 24/96 data were near perfect down to -120dBFS. We all also extended the sweep down to -140dBFS, to . . .
. . . see how well the 24/96 would perform. We can see here, only a +3/+1dB (L/R) overshoot at -140dBFS. This is an exemplary digital-linearity result.
Impulse response (24/44.1 data)
The graph above shows the impulse response for the RAS-5000, fed to the coaxial digital input, measured at the line-level pre-outputs, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period then back to digital silence. We find a reconstruction filter that minimizes pre-ringing, with short post-ringing.
J-Test (coaxial)
The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outputs of the RAS-5000 where 0dBFS is set to 2Vrms. J-Test was developed by Julian Dunn in the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g,, 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.
Here we see an average J-Test result, with peaks flanking the 12kHz fundamental, as high as -110dBrA. This is an indication that the RAS-5000 DAC may be susceptible to jitter.
J-Test (optical)
The chart above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outputs of the RAS-5000. The optical input yielded similar but slightly worse results compared to the coaxial input.
J-Test (coaxial, 10ns jitter)
The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the RAS-5000, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The results are very clear, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/- 2kHz jitter signal) manifest at near -100dBrA. This is further indication that the DAC in the RAS-5000 has poor jitter immunity. For this test, the optical input yielded effectively the same results.
J-Test (coaxial, 100ns jitter)
The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the RAS-5000, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are very clear, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/- 2kHz jitter signal) manifest at near -80dBrA. This is further indication that the DAC in the RAS-5000 has poor jitter immunity. For this test, the optical input yielded effectively the same results.
Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)
The chart above shows a fast Fourier transform (FFT) of the RAS-5000’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The gentle roll-off around 20kHz in the white-noise spectrum shows that the RAS-5000 does not use a brick-wall type reconstruction filter. There are very clear low-level aliased image peaks within the audio band at the -90dBrA and below level. The primary aliasing signal at 25kHz is prominent at -20dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -80dBrA.
RMS level vs. frequency vs. load impedance (1W, left channel only)
The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .
. . . is the same but zoomed in to highlight differences. Here we that the deviations between no load and 4 ohms are around 0.05dB. This is a strong result for a class-AB amp, and an indication of a low output impedance, or high damping factor. With a real speaker load, deviations measured just below the 0.05dB level—well below the threshold of audibility.
THD ratio (unweighted) vs. frequency vs. output power
The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange just under 137W (just shy of the rated 140W). The power was varied using the RAS-5000 volume control. Between 20Hz and 1kHz, all THD ratios are fairly constant and similar, between 0.001 and 0.002%. Between 1kHz and 20kHz, THD ratios were higher at higher power levels, but not by a significant margin. At 20kHz, we measured 0.002% at 1W, 0.003% at 10W, and 0.01% at 137W.
THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD ratios measured at the speaker-level outputs of the RAS-5000 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Into 4 ohms, the right channel outperformed the left by more than 10dB between about 2 and 20W. The right channel THD ratios into 4 ohms ranged from 0.002% at 50mW, down to nearly 0.0002% at 5W, then up to 0.002% at just shy of 200W, where the RAS-5000 protection circuit engaged and shut down the unit. THD ratios into 8 ohms ranged from 0.001% at 50mW, then down to 0.0003-0.0005% between 1 and 10W, then up to 0.002% at the “knee” at roughly 140W, then up to the 1% THD mark at 154W. Note that we were able to achieve 230W into 4 ohms (1% THD) with the RAS-5000 in Bench Mode, but only for a few seconds before the protection circuit engaged and shut down the unit.
THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD+N ratios measured at the output of the RAS-5000 as a function of output power for the line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track closely except for the left input into 4 ohms, which yielded about 5dB more THD+N from 10W to over 100W. Otherwise, THD+N ratios ranged from 0.02% at 50mW, down to 0.001% at 20 to 50W, then up to just below 0.002% at the 8-ohm “knee.”
THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)
The chart above shows THD ratios measured at the output of the RAS-5000 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 20W at the output into 8 ohms (and roughly 40W into 4 ohms, and 80W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find essentially identical THD ratios (0.0015%) into all three loads up to about 200Hz. From 2kHz to 20kHz, there is a roughly 7-8dB increase in THD every time the load is halved. At 20kHz, we measured 0.003% into 8 ohms, 0.009% into 4 ohms, and 0.02% into 2 ohms. This is a strong result, and shows that the RAS-5000 is stable into 2 ohms.
THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows THD ratios measured at the output of the RAS-5000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Generally, THD ratios into the real speakers were similar to the resistive dummy load, with the expection of the two-way speaker at 20 to 30Hz, and the three-way speaker at 10 to 20kHz. THD ratios hovered between 0.001 and 0.003% from 40Hz to 6kHz for all three loads. At 20Hz, the THD ratio was 0.04% into the two-way speaker, and at 20kHz, 0.008% into the three-way speaker. This is a relatively strong result, and shows that the RAS-5000 will yield consistently low THD results into real-world speaker loads.
IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows intermodulation distortion (IMD) ratios measured at the output of the RAS-5000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, between 0.001 and 0.003% from 2.5kHz to 20kHz. Another strong result.
IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows IMD ratios measured at the output of the RAS-5000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, between 0.002 and 0.005% from 40Hz to 1kHz. Another strong result.
FFT spectrum – 1kHz (line-level input)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at a low -100dBrA, or 0.001%, while subsequent signal harmonics are near and below -120dBrA, or 0.0001%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak and its harmonics (120, 180, 240, 300Hz, etc.) at the -105dBrA, or 0.0006%, and below level.
FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Both the signal and noise-related harmonic peaks are very similar to the analog FFT above, but for a higher noise floor (-135dBFS) due to the 16-bit depth.
FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. Both the signal and noise-related harmonic peaks are very similar to the analog FFT above.
FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)
Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and noise-related peaks below the -110dBrA, or 0.0003%, level. There are no signal related peaks above the -135dBFS noise floor.
FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)
Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and noise-related peaks below the -110dBrA, or 0.0003%, level. Signal-related peaks are difficult to discern above the -145dBFS noise floor.
FFT spectrum – 50Hz (line-level input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is the second (100Hz) and third (150Hz) signal harmonic at a low -100dBrA, or 0.001%. Noise related peaks can be seen at -105dBRA, or 0.0006%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values were set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110dBRa, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are at -105dBrA, or 0.0006%. This is a strong IMD result.
Intermodulation distortion FFT (line-level input, APx 32 tone)
Shown above is the FFT of the speaker-level output of the RAS-5000 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are at and below the very low -120dBrA, or 0.0001%, level. The low frequency peaks that rise near and above -110dBrA, are due to power-supply noise.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is just below -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -95dBrA, or 0.002%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is just below -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -95dBrA, or 0.002%.
Squarewave response (10kHz)
Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the RAS-5000’s slew-rate performance. Rather, it should be seen as a qualitative representation of the RAS-5000’s extremely high bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, due to the RAS-5000’s very extended bandwidth, we see a near-perfect squarewave, with sharp corners and no ringing.
Damping factor vs. frequency (20Hz to 20kHz)
The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 300, from 20Hz to roughly 15kHz, then a dip down to around 80 at 20kHz. This is a relatively strong damping factor result for an affordable class-AB amp.
Diego Estan
Electronics Measurement Specialist
Link: reviewed by Dennis Burger on SoundStage! Access on March 1, 2024
General Information
All measurements taken using an Audio Precision APx555 B Series analyzer.
The Dayton Audio HTA200 was conditioned for one hour at 1/8th full rated power (~4W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.
The HTA200 offers one pair of line-level analog inputs (RCA), one pair of moving-magnet (MM) phono inputs (RCA), an RCA sub output, one digital coaxial (RCA) input, one optical (TosLink) input, one USB digital input, a pair of speaker level outputs and one headphone output over 1/4″ TRS connector. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level, as well as phono.
Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, and 0dBFS digital input. The signal-to-noise (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 70W (4 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum.
Based on the inaccuracy and non-repeatability of the left/right volume channel matching (see table below), the HTA200 volume control is a potentiometer operating in the analog domain. The HTA200 overall volume range is from -59dB to +28.6dB (line-level input, speaker output).
Our typical input bandwidth-filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs frequency sweeps where a bandwidth of 10Hz–90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.
Volume-control accuracy (measured at speaker outputs): left-right channel tracking
Volume position | Channel deviation |
min | 11.5dB |
9 o'clock | 0.068dB |
12 o'clock | 0.3dB |
3 o'clock | 0.65dB |
max | 0.6dB |
Published specifications vs. our primary measurements
The table below summarizes the measurements published by Dayton Audio for the HTA200 compared directly against our own. The published specifications are sourced from Dayton’s manual provided with the review sample (note: the PDF availiable on Dayton's website shows much higher power ratings that are less realistic than those shown here). With the exception of frequency response, where the Audio Precision bandwidth was extended to 1MHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.
Parameter | Manufacturer | SoundStage! Lab |
Maximum power output (4 ohms, peak/IHF) | 140W | 148W |
RMS power output (4 ohms, 1.5% THD) | 70W | 82W |
Gain (line-level) | 29dB | 28.6dB/27.9dB (L/R) |
THD+N (at 70W into 4 ohms) | 1.5% | 1.4% |
Frequency response (analog line-level in) | 15Hz-20kHz (±1dB) | 15Hz-20kHz (±1dB) |
Input sensitivity (for 70W into 4ohms, max volume) | 630mVrms | 630/675mVrms (L/R) |
Channel separation (1kHz, 70W 4 ohms) | 53dB | 57dB |
SNR (1kHz, 70W 4 ohms, A-weighted) | 80dB | 90dB |
Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Maximum output power into 8 ohms (1% THD+N, unweighted) | 16.5W | 16.5W |
Maximum output power into 4 ohms (1% THD+N, unweighted) | 32W | 32W |
Maximum burst output power (IHF, 8 ohms) | 93W | 93W |
Maximum burst output power (IHF, 4 ohms) | 148W | 148W |
Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |
Crosstalk, one channel driven (10kHz) | -43.9dB | -46.5dB |
Damping factor | 108 | 85 |
Clipping no-load output voltage | 11.8Vrms | 11.8Vrms |
DC offset | <12mV | <6mV |
Gain (sub-out) | 3.2dB | N/A |
Gain (maximum volume) | 28.6dB | 27.9dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-41dB | <-41dB |
IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-31dB | <-31dB |
Input impedance (line input, RCA) | 15.3k ohms | 15.3k ohms |
Input sensitivity (70W 4 ohms, maximum volume) | 630mVrms | 675mVrms |
Noise level (with signal, A-weighted) | N/A | N/A |
Noise level (with signal, 20Hz to 20kHz) | N/A | N/A |
Noise level (no signal, A-weighted, volume min) | <175uVrms | <190uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <300uVrms | <420uVrms |
Output impedance (pre-out) | 2806 ohms | N/A |
Signal-to-noise ratio (70W into 4 ohms, A-weighted, 2Vrms in) | 89.8dB | 89.9dB |
Signal-to-noise ratio (70W into 4 ohms, 20Hz to 20kHz, 2Vrms in) | 88.0dB | 87.2dB |
Signal-to-noise ratio (70W into 4 ohms, A-weighted, max volume) | 81.1dB | 81.0dB |
Dynamic range (70W into 4 ohms, A-weighted, digital 24/96) | 92.4dB | 92.5dB |
Dynamic range (70W into 4 ohms, A-weighted, digital 16/44.1) | 91.3dB | 91.3dB |
THD ratio (unweighted) | <0.75% | <0.78% |
THD ratio (unweighted, digital 24/96) | <0.82% | <0.85% |
THD ratio (unweighted, digital 16/44.1) | <0.82% | <0.87% |
THD+N ratio (A-weighted) | <0.86% | <0.89% |
THD+N ratio (A-weighted, digital 24/96) | <0.90% | <0.95% |
THD+N ratio (A-weighted, digital 16/44.1) | <0.92% | <0.98% |
THD+N ratio (unweighted) | <0.75% | <0.78% |
Minimum observed line AC voltage | 126VAC | 126VAC |
For the continuous dynamic power test, the HTA200 was able to sustain 133W into 4 ohms (~7% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (13.3W) for five seconds, for five continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the HTA200 (except for the tubes) was only slightly warm to the touch.
Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Crosstalk, one channel driven (10kHz) | -47.2dB | -50.6dB |
DC offset | <10mV | <8mV |
Gain (default phono preamplifier) | 36.7dB | 36.7dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-40dB | <-40dB |
IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-40dB | <-40dB |
Input impedance | 52.8k ohms | 53.3k ohms |
Input sensitivity (to 10W with max volume) | 5mVrms | 5mVrms |
Noise level (with signal, A-weighted) | <1.6mVrms | <1.5mVrms |
Noise level (with signal, 20Hz to 20kHz) | <8.5mVrms | <3.4mVrms |
Noise level (no signal, A-weighted, volume min) | <0.170mVrms | <0.185mVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <0.290mVrms | <0.420mVrms |
Overload margin (relative 5mVrms input, 1kHz) | 15.8dB | 15.8dB |
Signal-to-noise ratio (10W, A-weighted, 5mVrms in) | 71.4dB | 72.8dB |
Signal-to-noise ratio (10W, 20Hz to 20kHz, 5mVrms in) | 56.6dB | 69.7dB |
THD (unweighted) | <0.79% | <0.75% |
THD+N (A-weighted) | <0.90% | <0.86% |
THD+N (unweighted) | <0.79% | <0.75% |
Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left and right channels |
Maximum gain | 2.8dB |
Maximum output power into 600 ohms (1% THD) | 15mW |
Maximum output power into 300 ohms (1% THD) | 29mW |
Maximum output power into 32 ohms (1% THD) | 25mW |
Output impedance | 10.5 ohms |
Maximum output voltage (1% THD into 100k ohm load) | 3.06Vrms |
Noise level (with signal, A-weighted) | <90uVrms |
Noise level (with signal, 20Hz to 20kHz) | <125uVrms |
Noise level (no signal, A-weighted, volume min) | <8.2uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <11uVrms |
Signal-to-noise ratio (A-weighted, 1% THD, 3Vrms out) | 92dB |
Signal-to-noise ratio (20Hz - 20kHz, 1% THD, 3Vrms out) | 89dB |
THD ratio (unweighted) | <0.035% |
THD+N ratio (A-weighted) | <0.035% |
THD+N ratio (unweighted) | <0.035% |
Frequency response (8-ohm loading, line-level input)
In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the HTA200 is not flat within the audioband (20Hz to 20kHz). There’s a +1dB rise in the frequency response at 40Hz and at nearly 20kHz. There’s also a -0.3dB dip at 5-7kHz. The HTA200 appears to be AC coupled (or at least purposefully high-pass filtered) with a -3dB point at 10Hz. There is extreme brickwall-type filtering at 20kHz, with a -3dB point at around 21.8kHz. There is a high probability that the analog input is digitized, because this type of brickwall filtering is easier to implement in the digital domain. Further evidence for this can be seen in the FFTs in this report. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.
Frequency response (8-ohm loading, line-level input, bass and treble controls)
Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +7.5/-6.5dB of gain/cut is available centered at 100Hz/8kHz.
Phase response (8-ohm loading, line-level input)
Above are the phase-response plots from 20Hz to 20kHz (wrapped, or every time the phase delay exceeds 360 degrees, the plot loops back up to +180 degrees) for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The HTA200 appears to invert polarity and yields an astonishing -60000 degrees of phase shift at 20kHz.
Frequency response (line-level sub out)
Above is the frequency-response plot (relative to 80Hz) measured at the line-level sub out of the HTA200. The same rise at 40Hz that was observed at the speaker-level outputs can be seen here. The -3dB point is just past 2kHz.
Frequency response vs. input type (8-ohm loading, left channel only)
The chart above shows the HTA200’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The pink trace is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the 24/192 dithered digital input signal is not shown because it yielded the same result as the 24/96 data. Because the HTA200 appears to digitize incoming analog signals, as well as resample all digital signals to 44.1kHz, the same brickwall-type behavior is seen right at 20kHz regardless of the input type. At low frequencies, there is slightly more extension for the analog input, with a -3dB point at 10Hz versus about 12Hz for the digital input. The digital input shows less significant deviations within the audioband, with a rise of only 0.5dB at 50Hz versus the 1dB rise at 40Hz for the analog input. The same is true at 20kHz, where the digital input is at +0.25dB compared to the +0.8dB for the analog signal.
Frequency response (8-ohm loading, MM phono input)
The chart above shows the frequency response (relative to 1kHz) for the phono input (MM configuration). What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). We see a maximum deviation of about -5dB/+0.8dB (20Hz and 20kHz) from 20Hz to 20kHz. The dip at 5-7kHz seen with the line-level input is also seen here; however, with a channel-to-channel deviation of about 0.3dB (from 5kHz to 20kHz).
Phase response (MM input)
Above is the phase-response plot from 20Hz to 20kHz (excess, or above and beyond the true input to output phase delay as seen in the plot for the line-level input above) for the phono input (MM configuration) measured across the speaker outputs at 10W into 8 ohms. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about +150 degrees at 20Hz.
Digital linearity (16/44.1 and 24/96 data)
The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the speaker outputs of the HTA200 at 1W into 8 ohms. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. The 16/44.1 data were essentially perfect as of -90dBFS down to 0dBFS, while the 24/96 data were near perfect down to -100dBFS. Both overshot the mark by over 10dB at -120dBFS. This is a poor linearity-test result, although it should be pointed that the linearity test is measured at the line-level pre-out when available. In this case, there are none, and the speaker outputs will invariably be noisier.
Impulse response (24/44.1 data)
The graph above shows the impulse response for the HTA200, fed to the coaxial digital input, measured at the speaker level output at 1W into 8ohms, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period then back to digital silence. We find a reconstruction filter that adheres to a typical symmetrical sinc function, although the HTA200 does invert polarity.
J-Test (coaxial)
The chart above shows the results of the J-Test test for the coaxial digital input measured at the speaker level output of the HTA200 at 1W into 8 ohms. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least-significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.
It is difficult to assess the results, with the significant rise in the noise floor (-80dBrA) centered on the main peak. We see a peak at -75dBrA at 8kHz, and another at -85dBrA at 16kHz. This is a poor J-Test result, indicating that the HTA200 DAC may be susceptible to jitter. When we attempted to inject artificial jitter at a level of only 10ns, we could not capture a reliable result.
J-Test (optical)
The chart above shows the results of the J-Test test for the optical digital input measured at the speaker-level output of the HTA200 at 1W into 8 ohms. The optical input yielded essentially the same result as the coaxial input.
Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)
The chart above shows a fast Fourier transform (FFT) of the HTA200’s speaker level output at 1W into 8 ohms, with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The steep roll-off around 20kHz in the white-noise spectrum shows the brickwall-type behavior of the HTA200’s reconstruction filter. There are low-level aliased image peaks within the audioband at the -100dBrA level. The primary aliasing signal at 25kHz cannot be seen and is completely suppressed, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -55dBrA.
RMS level vs. frequency vs. load impedance (1W, left channel only)
The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .
. . . is the same but zoomed in to highlight differences. Here we find that between 100Hz and 8kHz, the deviations between no load and 4 ohms are around 0.15dB. This is a fair result for a class-AB amp, and an indication of a relatively low output impedance, or high damping factor. Due to the nonlinear nature of the HTA200’s frequency response, it is difficult to assess the fluctuations in response versus frequency for the real speaker load.
THD ratio (unweighted) vs. frequency vs. output power
The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange just under 35W. The power was varied using the HTA200 volume control. At 1W, THD ratios are fairly constant at 0.3% from 20Hz to 20kHz. At 10W, THD ratios are fairly constant across the audioband from 1% to 0.8%, while at 35W, THD ratios are as high as 2% at 20Hz, then a constant 1.5% from 100Hz to 20kHz. The HTA200 is definitely a high-distortion amplifier, considering the class-AB transistor-based output.
THD ratio (unweighted) vs. frequency at 10W (MM input)
The chart above shows THD ratio as a function of frequency plots for the phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from around 0.5% to 0.8% across the audioband.
THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD ratios measured at the output of the HTA200 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track closely except for maximum power, with the 4-ohm data slightly outperforming (2-3dB) the 8-ohm data at medium power. THD ratios range from as low as 0.1% at 50mW, then a steady linear climb to the “knees” at 80W (2% into 8 ohms) and just past 100W (2% into 4 ohms). The 1% THD marks were reached at just 16.5W (8 ohms) and 32W (4 ohms).
THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD+N ratios measured at the output of the HTA200 as a function of output power for the line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track closely except for maximum power, with the 4-ohm data slightly outperforming (2-3dB) the 8-ohm data at lower power. Overall, THD+N values for both loads ranged from 0.2% at 50mW, then a steady linear climb to the “knees” at 80W (2% into 8 ohms) and just past 100W (2% into 4 ohms). Because THD ratios are so high with the HTA200, it’s the THD component of THD+N that dominates in these graphs.
THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)
The chart above shows THD ratios measured at the output of the HTA200 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find essentially identical THD ratios into all three loads, from 1% to 0.8%. Ordinarily, having all three data sets plot identically would be commendable; however, in this case, THD ratios are very high for a solid-state amplifier output.
THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows THD ratios measured at the output of the HTA200 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical THD ratios into all three loads, just above and below 0.3% to 0.8%. As above, ordinarily, having all three data sets plot identically would be commendable; however, in this case, THD ratios are very high for a solid-state amplifier output.
IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows intermodulation distortion (IMD) ratios measured at the output of the HTA200 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical IMD ratios into all three loads, around 0.3%. Once again, having all three data sets plot identically would be commendable; however, in this case, the IMD ratios are very high for a solid-state amplifier output.
IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows IMD ratios measured at the output of the HTA200 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical IMD ratios into all three loads, 1% from 40Hz to almost 500Hz, and then a dip to 0.02% from 500Hz to 1kHz. As mentioned above, having all three data sets plot identically would be commendable; however, in this case, the IMD ratios are very high for a solid-state amplifier output.
FFT spectrum – 1kHz (line-level input)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second (2kHz) harmonic dominates at a very high -40dBrA, or 1%, while subsequent signal harmonics are at and below -70dBrA, or 0.03%. On the right side of the signal peak, we see the primary (60Hz), second (120Hz), and fourth (240Hz) noise-related harmonics dominate at -85dBrA to -95dBrA, or 0.006% to 0.002%. While difficult to see in this graph, we did find two peaks at 43.1kHz and 45.1kHz, which are telltale IMD products that are a result of the 1kHz analog signal being digitized and sampled at 44.1kHz.
FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. We see that the signal’s second (2kHz) harmonic dominates at a very high -40dBrA, or 1%, while subsequent signal harmonics are at and below -55dBrA, or 0.2%. On the right side of the signal peak, we see the primary (60Hz), second (120Hz), and fourth (240Hz) noise-related harmonics dominate at -85dBrA to -95dBrA, or 0.006% to 0.002%.
FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. We see that the signal’s second (2kHz) harmonic dominates at a very high -45dBrA, or 0.6%, while subsequent signal harmonics are at and below -90dBrA, or 0.003%. On the right side of the signal peak, we see the primary (60Hz), second (120Hz), and fourth (240Hz) noise-related harmonics dominate at -85dBrA to -95dBrA, or 0.006% to 0.002%.
FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)
Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at just under the correct amplitude, and noise-related peaks at -90dBrA, or 0.003%, and below.
FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)
Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at just under the correct amplitude, and noise-related peaks at -90dBrA, or 0.003%, and below.
FFT spectrum – 1kHz (MM phono input)
Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input. We see that the signal’s second (2kHz) harmonic dominates at a very high -40dBrA, or 1%, while subsequent signal harmonics are at and below -70dBrA, or 0.03%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak dominate at -65/-75dBrA (left/right), or 0.06/0.02%.
FFT spectrum – 50Hz (line-level input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is the second (100Hz) signal harmonic at a high -40dBrA, or 1%. Several other signal-related harmonic peaks can be seen throughout at -70dBrA, or 0.03%, and below.
FFT spectrum – 50Hz (MM phono input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the MM phono input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the second (100Hz) signal harmonic at a high -45dBrA, or 0.6%. The worst-case noise-related peak is from the fundamental (60Hz) for the left channel at -60dBrA, or 0.1%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -45dBRa, or 0.6%, while the third-order modulation products, at 17kHz and 20kHz, are at -80dBrA, or 0.01%.
Intermodulation distortion FFT (line-level input, APx 32 tone)
Shown above is the FFT of the speaker-level output of the HTA200 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e. the “grass” between the test tones—are distortion products from the amplifier and are at and below the -70dBrA, or 0.03%, level.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are around -75dBrA, or 0.02%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are around -90dBrA, or 0.003%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are around -60dBrA, or 0.1%.
Squarewave response (10kHz)
Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the HTA200’s slew-rate performance. Rather, it should be seen as a qualitative representation of the HTA200’s extremely restricted bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, because of the brickwall-type cutoff at 20kHz, we find only the 10kHz fundamental sinewave, with all the upper harmonics filtered out.
Squarewave response (1kHz)
Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, We can see significant overshoot/undershoot in the corners of the squarewave, a consequence of the HTA200’s limited bandwidth.
Damping factor vs. frequency (20Hz to 20kHz)
The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 100, from 20Hz to 20kHz.
Diego Estan
Electronics Measurement Specialist
Link: reviewed by Dennis Burger on SoundStage! Access on February 1, 2024
General Information
All measurements taken using an Audio Precision APx555 B Series analyzer.
The Technics Grand Class SU-GX70 was conditioned for one hour at 1/8th full rated power (~5W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.
The SU-GX70 offers two line-level analog inputs (RCA), one moving-magnet (MM) phono input (RCA), one pair of preamp outputs (RCA), one digital coaxial (RCA) and two optical (TosLink) S/PDIF inputs, one USB digital inputs, two pairs of speaker-level outputs and one headphone output over 1/4″ TRS connector. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level, as well as phono.
The SU-GX70 is a sophisticated device that digitizes all incoming signals and can apply DSP for various functions. An “initialization” was performed before any measurements were made, to ensure that any room EQ DSP had been cleared. Unless otherwise stated, Pure Amplification was turned on, MQA off, and LAPC off, although comparisons between the on and off effects of these functions can be seen in this report.
Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input and 0dBFS digital input. The volume control is variable from -99dB to 0dB. The signal-to-noise (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 40W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum.
Based on the high accuracy and repeatability of the left/right volume channel matching (see table below), the SU-GX70 volume control operates in the digital domain. The SU-GX70 offers 1dB volume steps ranging from -99dB to -54dB, then 0.5dB steps from -53.5dB to 0dB. Overall range is -59.3dB to +39.6dB (line-level input, speaker output).
Because the SU-GX70 is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.
Volume-control accuracy (measured at speaker outputs): left-right channel tracking
Volume position | Channel deviation |
-99dB | 0.02dB |
-70dB | 0.026dB |
-60dB | 0.026dB |
-40dB | 0.022dB |
-30dB | 0.024dB |
-20dB | 0.022dB |
-10dB | 0.024dB |
0dB | 0.025dB |
Published specifications vs. our primary measurements
The table below summarizes the measurements published by Technics for the SU-GX70 compared directly against our own. The published specifications are sourced from Technics’ website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 250kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.
Parameter | Manufacturer | SoundStage! Lab |
Amplifier rated output power into 8 ohms (1% THD) | 40W | 50W |
Amplifier rated output power into 4 ohms (1% THD) | 80W | 94W |
Frequency response (analog line-level in, speaker out 4-ohm) | 20Hz-40kHz (-3dB) | 20Hz-46kHz (-3dB) |
Frequency response (digital in, speaker out 4-ohm) | 20Hz-40kHz (-3dB) | 20Hz-46kHz (-3dB) |
Frequency response (phono MM, speaker out 4-ohm) | RIAA 20Hz-20kHz (±1dB) | RIAA 20Hz-20kHz (±0.5dB) |
Input sensitivity (analog line-level in) | 200mVrms | 187mVrms |
Input impedance (analog line-level in) | 23k ohms | 29.6k ohms |
Input sensitivity (phono MM) | 2mVrms | 1.81mVrms |
Input impedance (phono MM) | 47k ohms | 53.9k ohms |
Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Maximum output power into 8 ohms (1% THD+N, unweighted) | 50W | 50W |
Maximum output power into 4 ohms (1% THD+N, unweighted) | 94W | 94W |
Maximum burst output power (IHF, 8 ohms) | 50W | 50W |
Maximum burst output power (IHF, 4 ohms) | 94W | 94W |
Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |
Crosstalk, one channel driven (10kHz) | -83.5dB | -83.2dB |
Damping factor | 38 | 38 |
Clipping no-load output voltage | 20.8Vrms | 20.8Vrms |
DC offset | N/A | N/A |
Gain (pre-out) | 21.4dB | 21.5dB |
Gain (maximum volume) | 39.7dB | 39.6dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-68dB | <-68dB |
IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-55dB | <-55dB |
Input impedance (line input, RCA) | 29.6k ohms | 29.6k ohms |
Input sensitivity (40W, maximum volume) | 187mVrms | 187mVrms |
Noise level (with signal, A-weighted) | <654uVrms | <654uVrms |
Noise level (with signal, 20Hz to 20kHz) | <745uVrms | <745uVrms |
Noise level (no signal, A-weighted, volume min) | <58uVrms | <51uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <73uVrms | <65uVrms |
Output impedance (pre-out) | 1.39k ohms | 1.39k ohms |
Signal-to-noise ratio (40W, A-weighted, 2Vrms in) | 100.5dB | 100.6dB |
Signal-to-noise ratio (40W, 20Hz to 20kHz, 2Vrms in) | 95.8dB | 93.7dB |
Signal-to-noise ratio (40W, A-weighted, max volume) | 80.4dB | 80.5dB |
Dynamic range (full power, A-weighted, digital 24/96) | 110.4dB | 111.6dB |
Dynamic range (full power, A-weighted, digital 16/44.1) | 95.6dB | 95.6dB |
THD ratio (unweighted) | <0.020% | <0.019% |
THD ratio (unweighted, digital 24/96) | <0.017% | <0.018% |
THD ratio (unweighted, digital 16/44.1) | <0.017% | <0.018% |
THD+N ratio (A-weighted) | <0.024% | <0.023% |
THD+N ratio (A-weighted, digital 24/96) | <0.020% | <0.021% |
THD+N ratio (A-weighted, digital 16/44.1) | <0.020% | <0.021% |
THD+N ratio (unweighted) | <0.022% | <0.021% |
Minimum observed line AC voltage | 125VAC | 125VAC |
For the continuous dynamic power test, the SU-GX70 was able to sustain 105W into 4 ohms (~6% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (10.5W) for five seconds, for five continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the SU-GX70 was only slightly warm to the touch.
Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left channel | Right channel |
Crosstalk, one channel driven (10kHz) | -75dB | -76dB |
DC offset | N/A | N/A |
Gain (default phono preamplifier) | 40.2dB | 40.2dB |
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-68dB | <-69dB |
IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-67dB | <-67dB |
Input impedance | 53.9k ohms | 52.4k ohms |
Input sensitivity (to 40W with max volume) | 1.81mVrms | 1.83mVrms |
Noise level (with signal, A-weighted) | <870uVrms | <800uVrms |
Noise level (with signal, 20Hz to 20kHz) | <1300uVrms | <1300uVrms |
Noise level (no signal, A-weighted, volume min) | <58uVrms | <50uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <73uVrms | <65uVrms |
Overload margin (relative 5mVrms input, 1kHz) | 26.3dB | 26.4dB |
Signal-to-noise ratio (40W, A-weighted, 5mVrms in) | 83.8dB | 83.8dB |
Signal-to-noise ratio (40W, 20Hz to 20kHz, 5mVrms in) | 77.5dB | 78.8dB |
Signal-to-noise ratio (40W, A-weighted, max volume) | 74.7dB | 74.8dB |
THD (unweighted) | <0.018% | <0.018% |
THD+N (A-weighted) | <0.022% | <0.022% |
THD+N (unweighted) | <0.023% | <0.023% |
Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 1Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):
Parameter | Left and right channels |
Maximum gain | 16.0dB |
Maximum output power into 600 ohms (1% THD) | 2.5mW |
Maximum output power into 300 ohms (1% THD) | 4.1mW |
Maximum output power into 32 ohms (1% THD) | 6.8mW |
Output impedance | 60 ohms |
Maximum output voltage (1% THD into 100k ohm load) | 1.34Vrms |
Noise level (with signal, A-weighted) | <15uVrms |
Noise level (with signal, 20Hz to 20kHz) | <28uVrms |
Noise level (no signal, A-weighted, volume min) | <13uVrms |
Noise level (no signal, 20Hz to 20kHz, volume min) | <16uVrms |
Signal-to-noise ratio (A-weighted, 1% THD, 1.1Vrms out) | 96.7dB |
Signal-to-noise ratio (20Hz - 20kHz, 1% THD, 1.1Vrms out) | 91.7dB |
THD ratio (unweighted) | <0.02% |
THD+N ratio (A-weighted) | <0.024% |
THD+N ratio (unweighted) | <0.021% |
Frequency response (8-ohm loading, line-level input)
In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the SU-GX70 is nearly flat within the audioband (20Hz to 20kHz). At the extremes the SU-GX70 is -0.1dB at 20Hz and +0.5dB down at 20kHz. There’s a rise in the frequency response above 20kHz, where we see +2.2dB just past 40kHz, which is a result of the digital amplifier and its high output impedance at high frequencies. Into a 4-ohm load (see RMS level vs. frequency vs load impedance graph below), the response is essentially flat at and above 20kHz. The -3dB point was also explored and found to be at roughly 46kHz, exactly where it was measured for a 24-bit/96kHz digital input signal (see “Frequency response vs. input type chart” below). In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.
Frequency response (8-ohm loading, line-level input, bass and treble controls)
Above is a frequency response (relative to 1kHz) plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/- 5dB of gain/cut is available at 20Hz/20kHz.
Phase response (8-ohm loading, line-level input)
Above are the phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The SU-GX70 does not invert polarity and exhibits at worst, 20 degrees (at 20Hz) of phase shift within the audioband.
Frequency response vs. input type (8-ohm loading, left channel only)
The chart above shows the SU-GX70’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace (overlapping the purple trace) is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 data exhibits brickwall-type filtering, with a -3dB at 21.1kHz. The 24/96 (and analog input) and 24/192 kHz data yielded -3dB points at 46.8kHz and 92.9kHz respectively. The analog data looks nearly identical to the 24/96 digital data, which is evidence for the SU-GX70 sampling incoming analog signals at 96kHz.
Frequency response vs. MQA (16/44.1)
The chart above shows the SU-GX70’s frequency response (relative to 1kHz) for a 16/44.1 dithered digital input signal from 5Hz to 22kHz using the coaxial input, with MQA turned on. We find no difference in the measured frequency response for 16/44.1 data input whether MQA is turned on or off.
Frequency response (8-ohm loading, MM phono input)
The chart above shows the frequency response (relative to 1kHz) for the MM phono input without (blue/red) and with (purple/green) the subsonic filter enabled. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). We see a maximum deviation of about +0.5/-0.2dB (150Hz and 20kHz/20Hz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 20Hz.
Phase response (MM input)
Above is the phase response plot from 20Hz to 20kHz for the MM phono input without (blue/red) and with (purple/green) the subsonic filter enabled, measured across the speaker outputs at 10W into 8 ohms. The SU-GX70 does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about +80 degrees at 20Hz without the subsonic filter and +160 degrees with the filter.
Digital linearity (16/44.1 and 24/96 data)
The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level output of the SU-GX70. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were only +2dB (left) and +4dB (right) above reference, while the 24/96 data were within +1dBFS.
Impulse response (24/44.1 data)
The graph above shows the impulse response for the SU-GX70 with MQA turned off (blue) and MQA turned on (purple), fed to the coaxial digital input, measured at the line level output, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period then back to digital silence. We find a reconstruction filter that adheres to a typical symmetrical sinc function. There appears to be no difference in the impulse response with MQA on or off through the coaxial input.
J-Test (coaxial, MQA off)
The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SU-GX70 with MQA turned off. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.
The coaxial input exhibits low-level rises (-135dBrA) in the noise floor within the audioband at 6.5kHz and 13kHz. This is a good J-Test result, indicating that SU-GX70 DAC should yield good jitter immunity.
J-Test (optical, MQA off)
The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the SU-GX70. The optical input yielded essentially the same result compared to the coaxial input.
J-Test (coaxial, MQA on)
The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SU-GX70 with MQA turned on. The result is similar to the one with MQA turned off, only slightly improved, with the rises in the noise floor no longer visible.
J-Test with 100ns of injected jitter (coaxial, MQA off)
Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved exceptional, with no visible sidebands at the 100ns jitter level, and only a spurious peak at 2kHz at the -135dBrA level. The coaxial input is shown, but both performed the same.
Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input, MQA off)
The chart above shows a fast Fourier transform (FFT) of the SU-GX70’s line-level output with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, with MQA turned off. The steep roll-off around 20kHz in the white-noise spectrum shows the behavior of the SU-GX70’s reconstruction filter. There are low-level aliased image peaks within the audioband at around 2kHz and 13kHz, at or near -120dBrA. The primary aliasing signal at 25kHz is at -95dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -80 and -60dBrA.
Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input, MQA on)
The chart above shows a fast Fourier transform (FFT) of the SU-GX70’s line-level output with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, with MQA turned on. The steep roll-off around 20kHz in the white-noise spectrum shows the behavior of the SU-GX70’s reconstruction filter. There are low-level aliased image peaks within the audioband at around 2kHz and 7kHz, at -120dBrA.
RMS level vs. frequency vs. load impedance (1W, left channel only)
The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .
. . . is the same but zoomed in to highlight differences. Here we find that between 20Hz and 6kHz, the deviations between no load and 4 ohms are around 0.45dB, but at high frequencies, the differences are larger, at about 1dB at 20kHz. This is a relatively poor result, and an indication of a relatively high output impedance, or low damping factor. When a real speaker is used, deviations are within around 0.4dB throughout the audioband.
RMS level vs. frequency (1W, left channel only, real speaker, LPAC on and off)
The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 20Hz to 20kHz. Both plots are for the Focal Chora 806 speaker, with (purple) and without (blue) LAPC enbaled. The SU-GX70 provides a feature called Load Adaptive Phase Calibration (LAPC). This feature measures the outputs of the amplifier while the speakers are connected using test tones to establish a correction curve to deal with the amplifier’s inherently high output impedance at high frequencies. The theoretical goal is to achieve a flat frequency response for the user’s speakers when LAPC is enabled. We can see here that the purple trace is not flat, but closer to ideal compared to when LAPC is disabled. When LAPC is disabled, deviations reach about 0.35dB, while only 0.15dB with LAPC enabled.
THD ratio (unweighted) vs. frequency vs. output power
The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange just under 40W. The power was varied using the volume control. At 1W, THD ratios are fairly constant and range from 0.02% at 20Hz, down to 0.01% from 40Hz to 6kHz. At 10W, THD ratios are as high as 0.3% at 20Hz, with a steady decline to 0.01% at 6kHz. At nearly 40W, THD ratios are as high as 0.6% at 20Hz, with a steady decline to 0.02% at 6kHz.
THD ratio (unweighted) vs. frequency at 10W (MM input)
The chart above shows THD ratio as a function of frequency plots for the MM phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from around 0.3% at 20Hz, then a steady decline down to 0.015% at 6kHz.
THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD ratios measured at the output of the SU-GX70 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track closely except for maximum power, with the 4-ohm data slightly outperforming the 8-ohm data at lower power. THD ratios range from as low as 0.0025% at 0.5-1W, up to 0.07% (8-ohm) and 0.2% (4-ohm) at the “knees” at just below 50W and 90W, respectively. The 1% THD marks were reached at just past 50W (8 ohms) and just shy of 100W (4 ohms).
THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms
The chart above shows THD+N ratios measured at the output of the SU-GX70 as a function of output power for the line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track closely except for maximum power, with the 4-ohm data slightly outperforming the 8-ohm data at lower power. Overall, THD+N values for both loads ranged from 0.05% at 50mW, down to near 0.01% at 3-5W, then up to the “knees,” as described in the caption for the chart directly above.
THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)
The chart above shows THD ratios measured at the output of the SU-GX70 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find roughly the same THD values of 0.02% from 1kHz to 6kHz for the 8- and 4-ohm data. From 20Hz to 1kHz, there is a roughly 5dB increase in THD every time the load is halved. However, even into a 2-ohm load, which the SU-GX70 is not designed to drive, THD ratios range from 0.3% at 20Hz, down to 0.03% from 1kHz to 6kHz.
THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows THD ratios measured at the output of the SU-GX70 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). In general, the measured THD ratios for the real speakers were close to the 8-ohm resistive load, hovering between 0.01 and 0.02% from 100Hz to 6kHz. The two-way Focal yielded the highest THD values (0.2% at 20Hz) at very low frequencies.
IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows intermodulation distortion (IMD) ratios measured at the output of the SU-GX70 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All IMD results are similar, hovering from 0.03 to 0.015% across the measured frequency range.
IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)
The chart above shows IMD ratios measured at the output of the SU-GX70 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Between 40Hz and 60Hz, all result are essentially identical, around -81dB. Above 60Hz, the highest IMD ratios are associate with the Paradigm speakers, rising up to -74dB from 100Hz to 250Hz. All IMD results are essentially identical, from 0.05% from 40Hz to 400Hz, then 0.025% from 500Hz to 1kHz.
FFT spectrum – 1kHz (line-level input)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics are at a relatively high -80dBrA, or 0.01%, while subsequent signal harmonics are at and below -90dBrA, or 0.003%. Since the SU-GX70 uses a switching power supply, there are no obvious peaks at 60Hz or subsequent harmonics. There are, however, several significant noise peaks (as high as -65dB, or 0.06%) that are likely a result of IMD products between the signal, it’s harmonics, and the high-frequency oscillator used in the class-D amplifier section. Of note is that the analyzer would ignore these peaks, which are actually larger in magnitude than the signal harmonics, when calculating THD. There is also a rise in the noise above 20kHz, characteristic of digital amplifiers. This is far from what is considered a clean FFT.
FFT spectrum – 1kHz (line-level input, Pure Amplification off)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input, but with Pure Amplification turned off. The FFT is similar to the FFT above, where Pure Amplification was turned on, except for low-level peaks (-120dBrA, or 0.0001%) that can be seen here at low frequencies that are not present in the first FFT.
FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Signal harmonics are different to the analog input FFT above. The second (2kHz) harmonic is low at -115dBRa, or 0.0002%, while the third (3kHz) harmonic is much higher, at -75dBrA, or 0.02%. Subsequent signal harmonics are at and below -90dBrA, or 0.003%. The same IMD peaks can also be seen here, as high as -65dB, or 0.06%, flanking the main 1kHz signal peak.
FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. The FFT is very similar to the 16/44.1 input FFT above, but for a more predominant second (2kHz) signal harmonic at -95dBrA, or 0.002%.
FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)
Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -130dBrA.
FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)
Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -135dBrA.
FFT spectrum – 1kHz (MM phono input)
Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input. We see the third (3kHz) signal harmonic dominating at around -75dBrA, or 0.02%. Other signal harmonics can be seen at -95dBrA, or 0.002%, and below. The most significant power-supply-related noise peaks can be seen at 60Hz at -85dBrA, or 0.006%. Higher-order power-supply-related peaks can also be seen at lower amplitudes. The same IMD peaks can also be seen here, as high as -65dB, or 0.06%, flanking the main 1kHz signal peak.
FFT spectrum – 50Hz (line-level input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is the third (150Hz) signal harmonic at a high -55dBrA, or 0.02%. Several other signal-related and IMD peaks can be seen throughout at -70dBrA, or 0.03%, and below.
FFT spectrum – 50Hz (MM phono input)
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the MM phono input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The 60Hz power supply fundamental can be seen at -90dBrA, or 0.003%. The most predominant (non-signal) peak is the third (150Hz) signal harmonic at a high -55dBrA, or 0.02%. Several other signal-related and IMD peaks can be seen throughout at -70dBrA, or 0.03%, and below.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at nearly -80dBrA, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are at roughly the same level.
Intermodulation distortion FFT (line-level input, APx 32 tone)
Shown above is the FFT of the speaker-level output of the SU-GX70 with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are below the -90dBrA, or 0.003%, level.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBRa, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1, MQA on)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1, with MQA turned on. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBRa, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. This is essentially the same result as with the FFT with MQA turned off.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBRa, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. This is essentially the same result as with the 16/44.1 IMD FFT.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)
Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -95dBRa, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are just below -80dBrA, or 0.01%.
Square-wave response (10kHz)
Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the SU-GX70’s slew-rate performance. Rather, it should be seen as a qualitative representation of the SU-GX70’s mid-tier bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, because of the digital nature of the amplifier, we see a 400kHz switching frequency (see 1MHz FFT below) riding on top of the squarewave.
Square-wave response (10kHz, restricted 500kHz bandwidth)
Above is the same 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz input bandwidth on the analyzer to filter out the 400kHz switching frequency. We can see significant over/undershoot in the corners of the squarewave, a consequence of the SU-GX70’s mid-tier bandwidth.
FFT spectrum (1MHz bandwidth)
Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input, with an extended 1MHz input bandwidth. This enables us to see the high-frequency noise above 20kHz reaching almost -70dBrA at 80kHz. We also see a clear peak at 400kHz, reaching just past -20dBrA, as well as its harmonics (800kHz, 1.2MHz). These peaks, as well as the noise, are a result of the digital amplifier technology used in the SU-GX70. However, they are far above the audioband—and are therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.
Damping factor vs. frequency (20Hz to 20kHz)
The final graph above is the damping factor as a function of frequency. We can see here the clear trend of a higher (although still poor in absolute terms) damping factor at low frequencies—around 35 from 20Hz to 3kHz, and then a decline down to 18 at 20kHz. This is a limitation of the digital amplifier technology used in the SU-GX70, and the reason Technics has incorporated their clever Load Adaptive Phase Calibration (LAPC) feature to compensate for losses into low impedances at high frequencies.
Diego Estan
Electronics Measurement Specialist
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