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Equipment Measurements

October 2007

Einstein The Absolute Tune Integrated 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, including 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 with both channels being driven; measurements made on left channel unless otherwise noted.
  • This integrated amplifier inverts polarity.
  • AC line current draw at idle: 1.5A
  • Input sensitivity for 1W output into 8 ohms, volume at maximum: 83.9mV
  • Input impedance @ 1kHz: 9.8k ohms
  • Output impedance at 50Hz: 0.031 ohms
  • Gain, output voltage divided by input voltage, volume at maximum: 33.7X, 30.6dB
  • Output noise, 8-ohm load, 1k-ohm input termination
    • Volume control at reference position
      • wideband: 0.17mV, -84.0dBW
      • A weighted: 0.037mV, -97.7dBW
    • Volume control full clockwise
      • wideband: 0.29mV, -79.8dBW
      • A weighted: 0.076mV, -91.4dBW
    • Volume control full counterclockwise
      • wideband: 0.11mV, -88.2dBW
      • A weighted: 0.022mV, -102.2dBW
Measurements Summary

Power output with 1kHz test signal

  • 8-ohm load at 1% THD: 62.6W
  • 8-ohm load at 10% THD: 75.7W

  • 4-ohm load at 1% THD: 92.7W
  • 4-ohm load at 10% THD: 110.8W


Einstein's The Absolute Tune is a medium-power hybrid integrated amplifier utilizing tubes for the front-end circuitry and a solid-state output stage. Overall gain of this unit is just a bit higher than normal power-amplifier-only gain, which is appropriate for an integrated unit.

Chart 1 shows the frequency response of the amp with varying loads. The high-frequency response is quite wide, with an approximate 3dB-down point in excess of 200kHz. Output impedance, as judged by the closeness of spacing between the curves of open-circuit, 8-ohm, and 4-ohm loading, is quite low in the audio band. The usual NHT dummy-load curve is not shown, as the variations in the response would not show. The variation with the NHT dummy load in the audio range is on the order of +/-0.05dB -- a negligible amount. In this design, the frequency response varies little with volume-control setting from full volume down to about 60dB below full, where the bass starts to rise below about 100 Hz -- probably an inaudible artifact at normal listening volumes.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. The amount of distortion rises steadily with power level, as is characteristic of most tube-based power amplifiers.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. The usual amount of rise in distortion at mid-to-high frequencies is admirably absent in this amplifier -- a desirable characteristic, but seen by this measurer in very few other amplifiers. There is a small anomaly in the distortion characteristic between 10kHz and 20kHz where the 5W and 10W distortion rises a small bit and the 30W distortion decreases.

Damping factor vs. frequency is shown in Chart 4 and is of a value and nature typical of many solid-state amplifiers being high up to about 1kHz and then rolling off with frequency.

A spectrum of the harmonic distortion and noise residue of a 10W 1kHz test signal is plotted in Chart 5. The magnitude of the AC line harmonics is very low and simple, and intermodulation components of line harmonics with signal harmonics, seen on many other amplifiers, are not present. Signal harmonics consist of a dominant second-order with higher-order harmonics falling off rapidly.

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

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

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

(line up at 30W to determine lines)
Top line: 8-ohm SMPTE IM
Second line: 4-ohm SMPTE IM
Third line: 8-ohm THD+N
Bottom line: 4-ohm THD+N

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

8-ohm output loading
Green line: 50W
Cyan line: 30W
Blue line: 10W
Magenta line: 5W
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 an 8-ohm load


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