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Equipment Measurements

May 2004

Audio Electronic Supply SixPac Mono Amplifiers: 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.

Additional Data
  • Measurements were made with 120V AC line voltage, using the 8-ohm output terminals, and with one channel driven (this is a mono amplifier).
  • Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination, 0dB feedback: wideband 1.14mV, -67.9dBW; A weighted 0.23mV, -81.8dBW.
  • Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination, 10dB feedback: wideband 3.78mV, -57.5dBW; A weighted 0.74mV, -71.6dBW.
  • AC line current draw at idle: 1.72A.
  • Output impedance at 50Hz (0dB feedback): 6.6 ohms.
  • Output impedance at 50Hz (10dB feedback): 2.1 ohms.
  • This amplifier does not invert polarity.  
Measurements Summary

Power output with 1kHz test signal

0dB feedback

  • 8-ohm load at 1% THD: 57W
  • 8-ohm load at 10% THD: 70W

  • 4-ohm load at 1% THD: 47W
  • 4-ohm load at 10% THD: 68W

10dB feedback

  • 8-ohm load at 1% THD: 58W
  • 8-ohm load at 10% THD: 72W

  • 4-ohm load at 1% THD: 53W
  • 4-ohm load at 10% THD: 68W

General

The Audio Electronic Supply SixPac is a moderate-power tube amp utilizing three pairs of triode-connected EL34 output tubes. Four- or 8-ohm load matching is provided for the output terminals with a two-position toggle switch. A front-panel switch gives the option of 0 or 10dB of negative feedback.

The following measurements were made with the output load selection switch set for 8 ohms. Relative behavior in the 4-ohm position was about the same for 4- and 2-ohm loading. Distortion was measured with the 10dB of feedback applied. In general, distortion without the feedback was about 2-3 times greater.

Chart 1a shows the frequency response of the amp with varying loads and with the 10dB of feedback engaged. Output impedance as judged by the spacing between the various loadings is typical of many tube power amplifiers. The effect on delivered frequency response to a typical speaker load is also shown for the NHT dummy load. Chart 1b is with no feedback. Here, the output impedance is much higher, and, in my personal opinion, too high with the consequence that the delivered frequency response to many speakers would be way off from flat. Chart 2 illustrates how total harmonic distortion plus noise versus power varies for 1kHz and SMPTE IM test signals and amplifier output load. In the case of this amplifier, the 4-ohm loading produces about the same power as with the more "matched" 8-ohm load. Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. Damping factor versus frequency is shown in Chart 4 for both the 0 and 10dB of feedback. A spectrum of the harmonic distortion and noise residue is plotted in Chart 5. As seems to be the case with many amplifiers measured, this one has a rich series of AC-line-hum harmonics with some sidebands of 120Hz about the nulled fundamental frequency. The harmonics series of the signal test frequency is quite dense and extends over the rest of the audio range.

Chart 1 - Frequency Response of Output Voltage as a Function of Output Loading


(Chart 1a: 10dB feedback)
Red line: open circuit
Magenta line: 8-ohm load
Blue line: 4-ohm load
Cyan line: NHT dummy-speaker load


(Chart 1b: 0dB feedback)
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


(10dB feedback)
(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: 8-ohm THD+N 

Chart 3 - Distortion as a Function of Power Output and Frequency


(10dB feedback)
8-ohm output loading
Cyan line: 50W
Blue line: 30W
Magenta line: 10W
Red line: 1W

Chart 4 - Damping Factor as a Function of Frequency


Damping factor = output impedance divided into 8
Red line: 10dB feedback
Magenta line: 0dB feedback

Chart 5 - Distortion and Noise Spectrum


(10dB feedback)
1kHz signal at 10W into an 8-ohm load

 

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