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
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.