Revox 750 (MKI & MKII) Stereoverstärker (1977 - 1982)

This compact full amplifier transfers even extreme Crescendi from breath to Furioso in impressive purity.

In order to be able to build the compact amplifier B750, only musical high points had to be analyzed and over nostalgic tubes strengthened.

The quality of an amplifier can be based not simply on its wattage, but to it, how distortion-free it shows the music.

Music disturbing often felt…
… because always it with noise connected. Today shrubs would speak probably rather of the distortion factor. In addition, it is nearly unbelievable, which an amplifier must carry out. It processes even high-complex signal forms both with smaller as well as with largest volume in such a manner purely that remaining distortions can be only proven with most modern measuring methods.

In order to avoid distortions, with the tube amplifier the inverse feedback principle was already used. Simply expressed: A part of the output signal is led back gegenphasig the entrance. The unevenness and distortions which are due to the reinforcement are waived by the revolution of the phase to a large extent.

In the transistor age one could increase this inverse feedback so strongly that rattle/clink became insignificant. But HiFi is now once a quality criterion, which one does not measure so much as feel can: The fine ears of fastidious Musikgeniesser discover physiological sound differences, to which with measuring instruments hardly is despite - or straight because of - this improvement to be gotten. They praise the warmer, rounder, fuller “tube sound” opposite the harder, cooler, more pointed Transsistorsound.

B750. The amplifier clean in itself
The research found out: Transistor amplifiers have more trouble opposite high-quality tube amplifiers with “transient ones”. Transiently is called volatilely, rapidly temporary - and transient ones occur in the music frequently: Shortest dynamic jumps, about a triangle clay/tone, a trill, a strong piano notice. They lead to short, but complex impulse distortions, which are too fast around a tiny little thing, when they could be corrected by the inverse feedback. Result: The amplifier is briefly overridden; the phase shift in the correction leads within the range of high frequencies to short, substantial distortions. While the “recovery period” the modulation which can be transferred is suppressed.

STUDER REVOX solved the problem of the TIM distortions (TIM or TID, transiently intermodulation Distortion) by complex measures: The output stage is full-complementary, symmetrical. Simply said: The positive and the negative side of the signal are symmetrically strengthened in separate transistors, from the entrance to the exit. The Einzelstufen are approximately coupled in itself, so that only a small total inverse feedback is necessary. Also without this total inverse feedback (factor 1:20) the amplifier is “clean”.

All this sounds plentifully complicated; all the more clearly however in such a way intensified music sounds, and that is in the long run crucial. The first TIM free Revox power amplifier A740, a professional high speed output stage, excited large attention among experts and with the descriptor “in itself more cleanly, by impulse distortions of free amplifiers” was distinguished. The same concept was used also with the compact amplifier B750. This trailblazing audio technology näherbringt certainly the HiFi rendition of the musical truthfulness a large step.

Technical data

Power output (DIN 45500)
220 Watts (110W per channel with 4 ohms)

Music
280 Watts (140W per channel with 4 ohms)

Distortions
better than 0.1%

Freqenzgang
20Hz-20kHz, 0,5dB

Unweighted signal-to-noise ratio
Tape better than 90dB
Phono better than 70dB

Cross talk (1kHz)
better than 66 railways for all entrances

Sound automatic controller, in 2-dB stages
8dB for bass, Treble, Presence

Assembly
99 transistors, 4 IC (voltage regulators) of 4 bridge rectifiers, 48 diodes

Weight
13 kg