Tuesday, September 19, 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 balanced inputs unless otherwise noted.

Power output (stereo mode)

  • Power output at 1% THD+N: 325.8W @ 8 ohms, 542.8W @ 4 ohms
  • Power output at 10% THD+N: 400.7W @ 8 ohms, 671.2W @ 4 ohms

Power output (mono mode)

  • Power output at 1% THD+N: 1100W @ 8 ohms, 1520W @ 4 ohms
  • Power output at 10% THD+N: 1430W @ 8 ohms, 2220W @ 4 ohms

Additional data

  • This amplifier does not invert polarity.
  • AC-line current draw at idle: 0.77A, 0.6PF, 54W
  • Gain: output voltage divided by input voltage, 8-ohm load
    •      Stereo mode: 35.9X, 31.1dB
    •      Mono mode: 71.9X, 37.1dB
  • Input sensitivity for 1W output into 8 ohms
    •      Stereo mode: 78.8mV
    •      Mono mode: 39.3mV
  • Output impedance @ 50Hz
    •      Stereo mode: 0.002 ohm
  • Input impedance @ 1kHz
    •      Stereo mode, unbalanced inputs: 47k ohms
    •      Stereo mode, balanced inputs: 95k ohms
    •      Mono mode, balanced input: 47.5k ohms
  • Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
    •      Wideband: 0.148mV/0.155mV, -85.6dBW/-85.2dBW
    •      A weighted: 0.051mV/0.053mV, -94.9dBW/-94.5dBW
  • Output noise (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
    •      Wideband: 0.176mV/0.152mV, -84.1dBW/-85.4dBW
    •      A weighted: 0.050mV/0.050mV, -95.0dBW/-95.0dBW
  • Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms
    •      Wideband: 0.217mV, -82.3dBW
    •      A weighted: 0.070mV, -92.1dBW

Measurements summary

Simaudio’s Moon Evolution 870A is a new high-power stereo amplifier design that replaces the Moon Evolution W-8. As the 870A is also capable of operating in bridged mono, some essential measurements were made in that mode as well.

Chart 1 shows the 870A’s frequency response with varying loads. Because the amp’s damping factor and resultant very low output impedance cause no noticeable change with output loading, the curve shown is the same for an open circuit, for loads of 8 and 4 ohms, and for an NHT dummy speaker. The results were substantially the same for mono mode (not shown).

Chart 2A illustrates how total harmonic distortion plus noise (THD+N) vs. power varies with 1kHz and SMPTE intermodulation (IM) test signals and amplifier output for loads of 8 and 4 ohms. Chart 2B shows the results for mono mode. Here, the IM curves reveal some abrupt increases in distortion at higher powers, which sometimes indicates HF instability with lower-impedance loading.

Charts 3A and 3B show THD+N as a function of frequency at different power levels for, respectively, the stereo and mono modes. The amount of rise in distortion at high frequencies is admirably low.

Damping factor vs. frequency is shown in Chart 4. This is extremely high, exceeding 500 at 20kHz. The damping factor in mono mode (not shown) was similar in shape but about half the magnitude.

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Chart 5. The magnitudes of the AC-line harmonics are relatively low; the signal harmonics are predominantly the second and third. The spectrum for the mono mode (not shown) is similar regarding the signal harmonics, but the AC-line harmonics have largely canceled, due to the differential subtraction action of similar signals.

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

Chart 1

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

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

Chart 2A

Chart 2A

Stereo mode
(Line up at 100W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 8-ohm THD+N
Bottom line = 4-ohm THD+N

Chart 2B

Chart 2B

Mono mode
(Line up at 100W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 8-ohm THD+N
Fourth line = 4-ohm THD+N

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

Chart 3A

Chart 3A

Stereo mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 100W
Green line = 250W

Chart 3B

Chart 3B

Mono mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 100W
Green line = 300W
Yellow line = 900W

Chart 4 - Damping factor as a function of frequency

Chart 4

Stereo mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Chart 5

Stereo mode
1kHz signal at 10W into a 4-ohm load

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