September 2002

PS Audio HCA-2 Stereo Amplifier: Measurements

All amplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test amplifiers there. All measurement data and graphical information displayed below are the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

• Measurements were made with 120V AC line voltage with both channels driven (worse of two channels plotted).
• Output noise, 8-ohm load: wideband 27.5mV, -40.2dBW (residual high-frequency switching noise at about 500kHz); A weighted 0.30mV, -79.5dBW.
• AC line current draw at idle: 0.24A.
• Output impedance (measured by an injection of a constant 1A of current at 50Hz): 0.14 ohms.
• This amplifier does not invert polarity.

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 150W
• 8-ohm load at 10% THD: 180W
  
  
• 4-ohm load at 1% THD: 250W
• 4-ohm load at 10% THD: 310W

General

Measurements were conducted on the HCA-2 with balanced inputs. Results with unbalanced input feed were substantially the same. Chart 1 shows the effect of loading on the frequency response at the 1W level. Like all switching power amplifiers, the response at the very high end of the audio band and beyond is influenced by the load because of the necessary LCR low-pass filters in the amplifier's output circuit. However, this is not likely to have much effect on the perceived frequency response with most speakers. The response variation shown in Chart 1 is perhaps less than seen in other designs. The frequency response with the NHT load is almost perfect. The amplifier's output impedance in the audio band is low enough that little variation of response with speaker impedance variation should be expected. Total harmonic distortion plus noise and SMPTE IM distortion is plotted vs. power output and loading in Chart 2. In order to not have the small amount of the switching-frequency residual at the output affect this data at low power, the special sharp Audio Precision Apogee 20kHz low-pass filter was used for this measurement. Amount of distortion is moderate in amount -- more in the arena of many tube power amplifiers rather than very-low-measuring solid-state designs. Total harmonic distortion plus noise vs. frequency at several power levels is shown in Chart 3. The amount of distortion does rise considerably with frequency. In this chart, the measurement bandwidth was 80 kHz to pass most of the highest-amplitude harmonics at the high end of the audio range. Chart 4 shows that the damping factor is reasonably high in the HCA-2 leading to good speaker damping. Chart 5 shows a spectrum of the harmonic distortion components for a 1kHz 10W signal with 8-ohm loading. The even harmonics are considerably lower than the odd harmonics indicating good plus/minus polarity symmetry. However, the amount of odd harmonic distortion is fairly high.

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

(line up at 10W to determine lines)
Top line: 4-ohm SMPTE IM
Second line: 8-ohm SMPTE IM
Third line: 4-ohm THD+N
Bottom line (red): 8-ohm THD+N

8-ohm output loading
Green line: 130W
Blue line: 50W
Magenta line: 10W
Red line: 1W

Damping factor = output impedance divided into 8

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

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