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Equipment Measurements

November 2001

Dehavilland Aries 845 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 at 120V AC line voltage.
  • Power output plotted with one channel driven (this is a mono amplifier).
  • Output tube plate current adjusted to 65mA.
  • Gain: 24.6x, 27.8dB.
  • Output noise, 8-ohm load: wideband 0.92mV, -70dBW; A weighted 0.15mV, -86dBW.
  • AC line current draw at idle: 1.9A.
  • Output impedance at 50Hz: 2 ohms.
  • This amplifier inverts polarity.
Measurements Summary

Power output with 1kHz test signal

  • 8-ohm load at 1% THD: 0.92W
  • 8-ohm load at 10% THD: 18W

  • 4-ohm load at 1% THD: 4.7W
  • 4-ohm load at 10% THD: 23W

  • 16-ohm load at 1% THD: 0.34W
  • 16-ohm load at 10% THD: 12W


Chart 1 shows a reasonable bandwidth of about 13Hz to 42kHz and a fairly high output impedance. The latter is shown by the drop of about 3.5dB from the "open circuit" line to the "4-ohm load" line. As can be seen in Charts 2 and 3, distortion is rather high in this design -- again typical for single-ended amps with no overall negative feedback. With its single non-selectable output connection, a 4-ohm load is optimum as evidenced by the lowest distortion in Chart 2 (see red line). This amp can put out 20W over most of the audio range at about 12-13% distortion (see Chart 3). At average listening levels of 1 to 2 watts with efficient speakers (say 90+ dB), distortion is acceptably low and should provide reasonable dynamics. The damping factor is on the low side at 4 (see Chart 4), but should be OK for many speakers. Lastly, the harmonic structure of a 10W signal as shown in Chart 5 shows the third harmonic higher than the second -- showing that the 4-ohm load as best output match and a desirable quick falloff of higher-order harmonics.

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

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

Chart 2 - Distortion as a Function of Power Output and Output Loading

Top line: 8-ohm SMPTE IM
Second line: 8-ohm THD+N
Third line: 2.7-ohm THD+N
Bottom line (red): 4-ohm THD+N

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

4-ohm output loading
Green line: 20W
Blue line: 10W
Magenta line: 3W
Red line: 1W

Chart 4 - Damping Factor as a Function of Frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and Noise Spectrum

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


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