Thursday, December 14, 2017

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All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Notes: Measurements were made at 120V AC line voltage with both channels being driven (stereo mode). Measurements were made on the left channel through the balanced input unless otherwise noted. The Audio Precision AUX-0025 measurement filter was used unless otherwise noted.

Power output (stereo mode)

  • Power output at 1% THD+N: 133.7W @ 8 ohms, 212.2W @ 4 ohms
  • Power output at 10% THD+N: 165.0W @ 8 ohms, 267.7W @ 4 ohms

Power output (mono mode)

  • Power output at 1% THD+N: 477.7W @ 8 ohms, 687.9W @ 4 ohms
  • Power output at 10% THD+N: 610.0W @ 8 ohms, 900.0W @ 4 ohms

Additional data

  • This amplifier does not invert polarity.
  • AC-line current draw at idle: 0.29A, 0.52PF, 17.7W
  • Gain (stereo mode): output voltage divided by input voltage, 8-ohm load
    •      Unbalanced inputs: 26.5X, 28.5dB
    •      Balanced inputs: 13.1X, 22.4dB
  • Gain (mono mode): output voltage divided by input voltage, 8-ohm load
    •      Unbalanced inputs: 52.6X, 34.4dB
    •      Balanced inputs: 26.2X, 28.4dB
  • Input sensitivity (stereo mode) for 1W output into 8 ohms
    •      Unbalanced inputs: 107.0mV
    •      Balanced inputs: 216.0mV
  • Input sensitivity (mono mode) for 1W output into 8 ohms
    •      Unbalanced inputs: 54.0mV
    •      Balanced inputs: 108.0mV
  • Output impedance @ 50Hz
    •      Stereo mode: 0.026 ohm
    •      Mono mode: 0.032 ohm
  • Input impedance @ 1kHz (stereo and mono modes)
    •      Unbalanced and balanced inputs: >700k ohms
  • Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
    •      Wideband (no AUX-0025 filter): 1.08V/1.10V, -8.4dBW/-8.2dBW
    •      Wideband: 1.5mV/1.25mV, -65.5BW/-67.1dBW
    •      A weighted: 0.22mV/0.23mV, -82.2dBW/-83.0dBW
  • Output noise (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
    •      Wideband (no AUX-0025 filter): 1.08V/1.09V, -8.4dBW/-8.3dBW
    •      Wideband: 1.48mV/1.23mV, -65.6dBW/-67.2dBW
    •      A weighted: 0.22mV/0.22mV, -82.2dBW/-82.2dBW
  • Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
    •      Wideband (no AUX-0025 filter): 1.56V, -5.2dBW
    •      Wideband: 1.68mV, -64.5dBW
    •      A weighted: 0.14mV, -86.1dBW
  • Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms
    •      Wideband (no AUX-0025 filter): 1.76V, -4.1dBW
    •      Wideband: 1.72mV, -64.3dBW
    •      A weighted: 0.11mV, -88.2dBW

Measurements summary

The Eximus S1 is a moderately powerful amplifier that uses a custom input buffer and input-switching circuit board, followed by a bridgeable ICEpower 250ASX2 switching amplifier.

Because the S1 can be switched between stereo and bridged-mono operation, measurements were taken of its performance in both modes. In each of the charts of the measurements, the suffix “A” indicates the mono-mode measurements.

Charts 1 and 1A show the frequency response of the S1 with varying loads. The amount of switching carrier noise in mono mode prevented getting a good measurable response without the Audio Precision AUX-0025 external filter, so the filter was used in both cases to provide comparable responses for stereo and mono operation. There is a bit more noticeable deviation of high-frequency response in mono mode, but of more interest is the rise in the low-frequency response. Apparently, the designers felt this would give more weight to the S1’s low-end sound.

Charts 2 and 2A illustrate how the S1’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation (IM) test signals and amplifier output load for 8- and 4-ohm loads. Testing into a 4-ohm load in mono mode caused the AC line fuse to blow. I was able to get a reading of THD+N once before the fuse blew, but couldn’t measure the SMPTE IM distortion because this test takes longer to run; the fuse blew before the test could be completed.

THD+N as a function of frequency at several different power levels is plotted in Charts 3 and 3A. High-frequency distortion rises considerably with increasing frequency; to keep the S1 from shutting down, the high-frequency limit was lowered to 6kHz at higher power levels.

The S1’s damping factor vs. frequency, shown in Charts 4 and 4A, is of a value and nature typical of many solid-state amplifiers: high up to about 1-2kHz, then rolling off with frequency.

A spectrum of the S1’s harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Charts 5 and 5A. The magnitude of the AC-line harmonics is relatively low, with some 60Hz showing in stereo mode but not in mono mode, the latter probably due to cancellation. The signal harmonics are low in amplitude and noticeably simpler, with a cleaner baseline, in mono mode.

Chart 1 - Frequency response of output voltage as a function of output loading

Chart 1

Stereo mode
Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 1A

Chart 1A

Mono mode
Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 2 - Distortion as a function of power output and output loading

Chart 2 

Stereo mode
(Line up at 10W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 4-ohm THD+N
Bottom line = 8-ohm THD+N

Chart 2A

Chart 2A 

Mono mode
(Line up at 10W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 4-ohm THD+N
Third line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

Chart 3

Stereo mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 60W
Cyan line = 100W

Chart 3A

Chart 3A

Mono mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 100W
Cyan line = 300W
Green line = 400W

Chart 4 - Damping factor as a function of frequency

Chart 4

Stereo mode
Damping factor = output impedance divided into 8

Chart 4A

Chart 4A

Mono mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Chart 5

Stereo mode
1kHz signal at 10W into an 8-ohm load

Chart 5A

Mono mode
1kHz signal at 10W into an 8-ohm load

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