Revox B 750 (1980)

Revox B750 Amplifier

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 Revox B750, only musical high points had to be analyzed and over nostalgic tubes strengthened. The quality of an Revox B750 amplifier can be based not simply on its wattage, but to it, how distortion-free it shows the music. 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 attributed gegenphasig again to 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 Revox B750 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.

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 Revox B750 amplifier is "clean". All this sounds plentifully complicated; the more clearly however the 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 Revox B750. This trailblazing audio technology naeherbringt certainly the HiFi rendition of the musical truthfulness a large step.

Revox 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 Revox B750 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.

Specifications

Power Output: 60 watts into 4 ohms; 40 watts into 8 ohms

Total Harmonic Distortion: less than 0.2 % at any level up to rated output

Frequency response: 20 Hz - 20 kHz ±0.5 dB

Damping factor: better than 75 at 8 ohms

Inputs (sensitivity for 60 watts (4 ohms) / input im­pedance):

Tuner, Aux, Tape 1 +2: 200 mV/100 kohms

Phono 1: 1.5 - 7 mV/25, 50, 100 kohms (selectable)

Phono 2: 1.5 - 7 mV; nominal 5 mV/50 kohms

PWR AMPIN: 1 V/10 kohms

Overload levels:

Tuner, Aux, Tape 1+2: 9V

Phono 1, 2: 400 mV

Outputs:

Tape 2/Out (DIN): 6.5 mV/RL 10 kohms

Speakers A, B: 15.5 V/R min. 4 ohms;

Tape 1, 2 (phono sockets): 200 mV/RL min. 50 kohms

Tape 2 (Jack): 200 mV/RL min. 50 kohms

PRE AMP Out: 1 V/RL min. 10 kohms

Phones x 2: 15.5V/Ri 100 ohms

Signal to noise ratio, (with reference to 60 watts / 4 ohms):

Tuner, Aux, Tape 1, 2: better than 90 dB, (unweighted input termination 10 kohms)

Phono 1, 2: better than 70 dB, (unweighted input termination 2.2 kohms)

Channel separation (at 1000 Hz): better than 60 dB

Phono equalization (as per I EC 98 MOD 4 1976): 20 Hz - 20 kHz ± 0.5 dB

Tone controls:

Bass: ±8 dB in 2 dB steps at 120 Hz

Treble: ±8 dB in 2 dB steps at 8 kHz

Presence: ±8 dB in 2 dB steps at 3 kHz

Filter:

Low: 50 Hz, -3 dB (12 dB/octave)

High: 8 kHz, -3 dB (12 dB/octave)

Loudness: Volume -30 dB, 100 Hz; + 6dB, 10 kHz + 4dB

Semiconductors:

4 IC (voltage regulation), 107 transistors, 4 bridge rectifiers, 52 diodes

Current supply: 220/240 V, 50/60 Hz

Power consumption: 50 - 350 watts

Dimensions (W x H x D): 452 x 151 x 348 mm (17,8 x 6 x 13,7 inch)

Weight: 13 kg (28 lbs 10 ozs)