The B77 was available in quarter track or half track and was a two speed recorder, quarter track 3.75 – 7.5 ips or half track 7.5 – 15 ips. Studer-Revox manufactured their own capstan and motors. These motors were electronically controlled and are given higher starting voltage slowly reducing to regular voltage for fast starts and smooth tape handling.
The capstan motor employs a precision-machined set of teeth at the circumference of its motor. As the motor turns, these teeth create a series of pulses that are read by a tachometer head and whose rate is compared against the frequency of a stable internal oscillator. In this way, even very slightest speed variations are immediately detected through a fast-acting servo system. To reduce wow and flutter even further, the direct-drive capstan shaft is machined to an accuracy of one one-thousandth of a millimeter, is hard chrome-plated and is artificially aged during the manufacturing process to ensure long-term stability. A 4th head could be added for audio-video control or slide-projector synchronization.
The Mk II version is the same as the Mk I except it adds a speed adjustment knob under the built-in editing block.
Infrared sensor automatic shut-off
2 AC reel motors; 1 AC capstan motor, electronically regulated
Wow & flutter
15 ips less than 0,06%
7.5 ips less than 0.08%
3.75 ips less than 0.1% at 3¾ ips
Frequency response (-20 VU)
15 ips
30 Hz … 22 kHz +2 / -3 dB
50 Hz … 18 kHz ± 1.5 dB
7.5 ips
30 Hz … 20 kHz +2 / -3 dB
50 Hz … 15 kHz ± 1.5 dB
3.75 ips
30 Hz … 16 kHz +2 / -3 dB
50 Hz … 10 kHz ± 1.5 dB
Signal to noise ratio 2 track
3.75 ips better than 64 dB
7.5 ips better than 67 dB
15 ips better than 65 dB
Signal to noise ratio 4 track
7.5 ips better than 63 dB
3.75 ips better than 60 dB
Equalization (NAB): 3¾ ips: 90 microsec / 3180 microsec: 7½ ips: 50 microsec / 3180 microsec / Crosstalk: at 1kHz stereo >45dB, mono >60dB / Distortion: 3¾ ips at 0VU <1%, at 0VU+6dB <2.5%. 7½ ips at 0VU <0.6%, at 0VU+6dB <1.5% / Level metering: VU meter as per ASA standard, with LED peak level indicators / Peak recording level: 514 nWb / m corresponds to 6dB above 0VU / Erase ratio: at 7½ ips >75dB / Semi-conductors: 11 ICs, 1 opto-coupler, 4 triacs, 60 transistors, 33 diodes, 5 LEDs, 2 full wave rectifiers, 3 relays / Rewind speed: approximately 135 seconds for 3,600 ft of tape / Inputs: mic Lo 0.15mV / 2k2ohms for low impedance microphones mic Hi 2.8mV / 110kohms for high impedance microphones radio 2.8mV / 20kohms aux 40mV / 220kohms / Outputs: amplifier: 1.55V / 390ohms adjustable with preset radio: 1.55V / 4k7ohms adjustable with preset headphones: 5.6V / 220ohms adjustable with control / Half or quarter-track stereo versions produced