Monday, February 19, 2018

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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: The PS Audio Stellar M700 was measured at 120V AC line voltage at its balanced input, unless otherwise noted. The Audio Precision AUX-0025 external filter was used for all measurements -- again, except as noted.

Power output

  • Power output at 1% THD+N: 357.0W @ 8 ohms, 712.0W @ 4 ohms
  • Power output at 10% THD+N: 465.0W @ 8 ohms, 930.0W @ 4 ohms

Additional data

  • Input/output polarity: noninverting
  • AC-line current draw
    • Operate: 20.0W, 0.28A, 0.56PF
    • Standby: 11.0W, 0.18A, 0.52PF
  • Gain: output voltage divided by input voltage, 8-ohm load
    • Balanced input: 33.9X, 30.6dB
    • Unbalanced input: 33.9X, 30.6dB
  • Input sensitivity for 1W output into 8 ohms
    • Balanced input: 83.4mV
    • Unbalanced input: 83.4mV
  • Output impedance @ 50Hz (see text): 0.022/0.0081 ohm
  • Input impedance @ 1kHz
    • Balanced input: 98.8k ohms
    • Unbalanced input: 50.0k ohms
  • Output noise, 8-ohm load, balanced/unbalanced inputs without AUX-0025 filter
    • Wideband: 0.98V, -9.2dBW
  • Output noise, 8-ohm load, unbalanced input terminated with 1k ohms
    • Wideband: 1.58mV, -65.1dBW
    • A weighted pin 3 of B input open: 179.0uV, -84.0dBW
    • A weighted pin 3 of B input connected to pin 1 (ground): 147.7uV, -85.6dBW
  • Output noise, 8-ohm load, balanced input terminated with 600 ohms
    • Wideband: 1.57mV, -65.1dBW
    • A weighted: 151.6uV, -85.4dBW

Measurements summary

The M700 mono power amp is a member of PS Audio’s new Stellar line of models. Its circuitry comprises a combination of a special PS Audio Gain Cell front end and a powerful class-D power amp section.

Chart 1 shows the M700’s frequency response with varying loads. Like most class-D circuits, this one has some out-of-band high-frequency peaking. Note that these data were taken without the AUX-0025 external filter, to reveal the amp’s true out-of-band HF response. Note also that the level at the high-frequency end of the chart does not continue to attenuate, due to the almost 1V of switching output noise.

Chart 2 illustrates how the M700’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE intermodulation test signals and amplifier output into loads of 8 and 4 ohms. The amount of distortion is low, and is dominated by noise up to about 10W, above which it rises smoothly to the onset of clipping.

The PS Audio’s THD+N as a function of frequency at several different power levels is plotted in Chart 3. Here, the increase in distortion with frequency is rather pronounced.

The M700’s damping factor vs. frequency is shown in Charts 4A and 4B. The amplifier has two sets of output terminals, the wire pairs of each going back to the actual single output of the class-D amplifier. When the damping factor measurement is driven and measured at one of these outputs, the damping factor is lower with a higher output impedance than when measured at the other, undriven output terminals. This difference is due to the resistance of the internal wire pair being driven and measured.

Chart 5 plots the spectrum of the Stellar M700’s harmonic distortion and noise residue of a 10W, 1kHz test signal. The AC line harmonics are below the level of the noise, and the signal harmonics are dominated by low amounts of the second and third harmonics.

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

Chart 1

Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load
Cyan line = NHT dummy-speaker load

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

Chart 2

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

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

Chart 3

(4-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 100W
Cyan line = 300W
Green line = 600W

Chart 4 - Damping factor as a function of frequency

Chart 4A - measured at output terminals

Chart 4A

Damping factor = output impedance divided into 8

Chart 4B - measured at internal output

Chart 4B

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Chart 5

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

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