Tuesday, January 17, 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.

Note: Measurements were made at 120V AC line voltage with both channels being driven. Measurements made on left channel through the balanced inputs unless otherwise noted.

Power output

  • Output power at 1% THD+N: 198.4W @ 8 ohms, 285.5W @ 4 ohms
  • Output power at 10% THD+N: 246.1W @ 8 ohms, 365.1W @ 4 ohms

Additional data

  • This amplifier does not invert polarity.
  • AC-line current draw at idle: 2.49A, 0.76PF, 233W
  • AC-line current draw at standby: 0.28A, 0.64PF, 21.8W
  • Gain: output voltage divided by input voltage, unbalanced and balanced inputs: 17.5X, 24.9dB 
  • Input sensitivity for 1W output into 8 ohms, unbalanced and balanced inputs: 161.6mV
  • Output impedance @ 50Hz: 0.153 ohm
  • Input impedance @ 1kHz, unbalanced and balanced inputs: >800k ohms
  • Output noise, 8-ohm load, balanced inputs, termination 600 ohms, Lch/Rch
    •      Wideband: 0.58mV/0.58mV, -73.8 dBW/-73.8dBW
    •      A weighted: 0.085mV/0.085mV, -90.4dBW/-90.4dBW
  • Output noise, 8-ohm load, unbalanced inputs, termination 1k ohm, Lch/Rch
    •      Wideband: 0.58mV/0.58mV, -73.8 dBW/-73.8dBW
    •      A weighted: 0.085mV/0.084mV, -90.4dBW/-90.5dBW

Measurements summary

The Ayre Acoustics VX-5 is a medium-power stereo amplifier. Like previous Ayre power amplifiers, it is fully balanced and uses no overall negative feedback.

Chart 1 shows the VX-5’s frequency response with varying loads: very flat throughout the entire test range of 10Hz-200kHz. The output impedance is low, but still high enough that you can just see the effects of changes in load on the vertical scale used for FR charts. The response to a dummy NHT speaker load is barely discernible between the limits of an open circuit and a 4-ohm load, which indicates that the impedances of most speakers won’t materially affect the VX-5’s frequency-response output.

Chart 2 illustrates how total harmonic distortion plus noise (THD+N) vs. power varies with 1kHz and SMPTE intermodulation (IM) test signals and amplifier output load for 8- and 4-ohm loads. The amount of distortion and how it rises with output level is similar to some other MOSFET power amps I have measured recently.

THD+N as a function of frequency at different power levels is plotted in Chart 3. The amount of rise in distortion at high frequencies is reasonably low in this design.

Damping factor vs. frequency, shown in Chart 4, is of a quality rarely seen in power amplifiers: flat throughout the audioband! I can remember only a very few other designs that achieved this.

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 very low and simple except for a few clustered around the suppressed 1kHz test signal. The dominant signal harmonic is the third, a testament to the circuitry’s basic symmetry.

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 load

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

Chart 2

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

Chart 3

(4-ohm loading)
Red line = 2W
Magenta line = 20W
Blue line = 100W
Cyan line = 200W
Green line = 250W

Chart 4 - Damping factor as a function of frequency

Chart 4

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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