Studer Revox A 76 Mulitplex Stereo Tuner

The A 76 multiplex stereo tuner was developed in conjunction with the A 77 recorder for the highest demands of radio reception. It did not appear until 1969, two years after the A 77. Based on the criteria for interference-free FM stereo reception, particular emphasis was placed on the following properties during development: high spurious wave suppression, high selectivity, low modulation distortion, large demodulator and limiter bandwidth, stable and interference-free stereo decoding, good interference pulse suppression, high sensitivity.

The A 76 is a sophisticated device designed by development engineer Ernst Mathys. A quadruple variable capacitor tuning guarantees excellent selection before the mixing stage, resulting in a side-wave suppression of more than 90 dB. Together with modern dual-gate field-effect transistors, the front end achieves optimum characteristics. An extremely stable local oscillator has been developed in order to avoid the negative effects of an AFC. Selection and amplification for the IF section were separated, with a passive 8-circuit Gaussian filter taking over the selection. The five-stage IF differential amplifier, together with the discriminator, has an unrivalled bandwidth of 5 MHz, which pays off in the form of high freedom from distortion. The broadband FM discriminator is not constructed with resonant circuits, but with two coaxial delay lines that cannot be out of tune. The stereo decoder works with a PLL oscillator and combines the advantages of high phase stability and symmetry with optimum channel separation. The signal strength display has an almost logarithmic curve, which means that strong and weak transmitters can be assessed equally. (Source: studerundrevox.de)