Rotel RAS-5000 Streaming Integrated Amplifier Measurements

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

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.

*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):

*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):

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