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.
 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, 8ohm load, 1kohm 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
Power output with 1kHz test signal
 8ohm load at 1% THD: 62.6W
 8ohm load at 10% THD: 75.7W
 4ohm load at 1% THD: 92.7W
 4ohm load at 10% THD: 110.8W
General
Einstein's The Absolute Tune is a mediumpower hybrid
integrated amplifier utilizing tubes for the frontend circuitry and a solidstate output
stage. Overall gain of this unit is just a bit higher than normal poweramplifieronly
gain, which is appropriate for an integrated unit.
Chart 1 shows the frequency response of the amp with
varying loads. The highfrequency response is quite wide, with an approximate 3dBdown
point in excess of 200kHz. Output impedance, as judged by the closeness of spacing between
the curves of opencircuit, 8ohm, and 4ohm loading, is quite low in the audio band. The
usual NHT dummyload 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
volumecontrol 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
tubebased 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 midtohigh 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 solidstate 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 secondorder with higherorder harmonics falling off rapidly.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
Red line: open circuit
Magenta line: 8ohm load
Blue line: 4ohm load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
(line up at 30W to determine lines)
Top line: 8ohm SMPTE IM
Second line: 4ohm SMPTE IM
Third line: 8ohm THD+N
Bottom line: 4ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
8ohm 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 8ohm load
