What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Revox A 77 (1967)

The REVOX A77 is an open reel tape recorder designed to fill the needs of the serious audiophile and the professional industry. It is a maximum performance machine that offers everything we believe to be value for use in the living room and for on-location recording, most importantly, uninterrupted recording time with convenience and ease of use, and maximum electronic and mechanical performance.

The REVOX A77 will make and replay tapes to professional standards. Indeed thousands of REVOX machines are used world wide for this purpose. An PL disk of outstanding quality can be cut from a carefully made REVOX recording and the performance of the machine is a match for the finest audio equipment available today. All facilities required in modern recording techniques are catered for, including sound on sound recording, multiplay, echo, on-off tape monitoring as well as playback to both European and American equalization standards. Further, the REVOX A77 will operate both horizontally and vertically and can accommodate even 10.5 inch (26,5 cm) diameter tape spools. The use of relays and solenoids permits all tape transport functions to be operated by remote control, including going, into the record mode.

Other important advantages of the new REVOX tape recorder A77 are calibrated VU-meters, a photo-electric end-of-tape switch, a four-digit tape position indicator and a separate output for stereo headphones with its own volume and balance controls. Facilities for switching off the spooling motors and a special button for tape editing.


The new REVOX A77 employs the classic three motor tape-transport system. The recently developed capstan motor drives the tape at constant speed.

Two further motors provide back tension from the feed spool and a constant take-up tension for the take-up spool. Furthermore, these motors, which are of original low weight-high torque design, permit a very smooth and fast tape wind. Only with three motors is it possible to provide each of the tape drive functions with the optimum characteristics. The same applies to the electro-magnetically operated servo-assisted brakes, which have proven themselves in the professional studio machines, as well as in previous REVOX.


The speed of the new capstan motor is no longer governed by the mains frequency as in the case of the usual synchronous or nonsynchronous motors. The speed of the motor is measured by means of a tacho head which does not touch the moving parts and kept constant by means of the electronic governor. The new motor will run at an extremely constant speed independent of the mains frequency.


With the development of an electronically governed capstan motor REVOX have once again pioneered in the field of magnetic recording. The new motors are smaller, lighter and has much lower current consumption and considerable reserve power. Furthermore, the speed constancy is completely independent of the normal mains frequency and voltage fluctuations.


The change in the motor revolution: for the two tape speeds of 7 1/2 ips (19 cm/sec) and 3 3/4 ips (9,5 cm/sec) is effected by means of the electronic governor. The speed change is effected by means of one single low current switch ensuring high reliability and long life.


The rigid die-cast head block holds three stereo heads. Two of them, the separate record and replay heads, are all-metal professional heads. These high quality heads were specially developed for the REVOX tape recorder A77 These heads ere the result of valuable experience, which we gained in the construction of all-metal heads for studio tape recorders.


Are used throughout the series A77. The types used are all metal cased thus ensuring maximum stability and long life. Where condenser values are critical tantalum has been chosen. All the amplifier electronics are built on plug-in printed circuit boards. The contacts do not have the usual tinned coating, but ere heavily gold plated over a hard nickel skin. This process has already proved highly successful in our transistorised studio machines.

The cable connections between the individual sub-assemblies are also made via plugs and sockets. Although an expensive method of construction we can thereby guarantee high reliability and serviceability. The electronic stabilisation of the supply voltage to the amplifiers and the oscillator make the performance of the machine independent of mains voltage fluctuations. Together with the electronically governed capstan motor this ensures important advantages when driving the machine from a battery by means of vibrators or rotary converters.

The tradition of quality at the REVOX works is based on several decades of experience in the manufacture of high quality tape recorders. Our experienced engineers and technicians have advanced the fundamental concepts of tape recorder design in the development of the REVOX A77. In addition they have developed a matching range of high fidelity units which are capable of making full use of the performance of the REVOX A77 hereby providing the discriminating music lover or professional user, with a complete system of unparallel excellence. The system comprises a high power hi-fi amplifier of 2 x 40 Watts with silicone planar transistors throughout. A supreme FM-tuner with 'field effect' input stage and integrated IF circuit designed to give the highest quality stereo FM reception, even under the most difficult conditions.

Mechanical Specifications

Tape Transport:

Three Studer eddy current motors. Electronically governed capstan motor. Electronic speed change. Solenoid operated via 3 relays.

Tape Speeds:

3¾ and 7½ ips (9,5 cm and 19 cm/sec.) ± 0.2%

High speed Version: 7½ and 15 ips (19 cm and 38 cm/sec.) ± 0.2%

Wow and Flutter:

max. ± 0.04% at 15 ips

max. ± 0.08% at 7½ ips

max. ± 0.1% at 3¾ ips (Weighted at DIN Standard 45507)

Tape Slip:

Less than 0.2%

Reel Diameter:

Maximum 10.5" (26,5cm)

(Minimum hub diameter 23/8 inches)

Forward / Rewind:

Fast winding time for 1800' (1100m) is 92 seconds

Tape Heads:

Three (Separate precision erase, record and playback heads.) Patented 'True Radius' design ensures excellent S/N ratio and head wrap

Guide System:

The Heads, the capstan drive, and the machines tape guides are mounted to a one-piece casting to maintain precise alignment.

Operating position:

Horizontal or Vertical

Electrical Specifications


Individual stereo record and playback heads with separate preamps, plus separate record and play circuits permit full source-tape monitoring.


NAB Standard on both record and playback at all speeds.

IEC Standard switchable on playback only.

Record Playback Frequency Response (Based on Revox 601):

15 ips - 30 Hz - 20 kHz ± 1.5 dB

7½ ips - 30 Hz - 20 kHz + 2 / - 3 dB

3¾ ips - 30 Hz - 16 kHz + 2 / - 3 dB

Signal-to-Noise Ratio:


15 ips - better than 66 dB

7½ ips - better than 66 dB

3¾ ips - better than 63 dB


15 ips - better than 62 dB

7½ ips - better than 62 dB

3¾ ips - better than 59 dB

Add 4 dB to the above figures with Dolby on, referenced to less than 2% THD

(Reference with Scotch 203 or Revox 601 or equivalent. Weighted as per CCITT C-curve to exclude supersonic bias noise.)

Distortion at full modulation at 1 kHz:

Max. 2% at 15 ips and 7½ ips.

Max 3% at 3¾ ips.

Crosstalk at 1 kHz:

Stereo, better than 45 dB

Mono, better than 60 dB

Bias frequency:

120 kHz, push-pull oscillator. Designed for low noise, high output tapes

Input sensitivity per channel:

Microphone, switchable LOW/HIGH

LOW: 50 - 600 ohms (unbalanced) 15mV

HIGH: up to 100 K ohms 2.5 mV

RADIO: 33 K ohms 2.5 mV

AUX: 1 M ohms 33 mV

Output per channel:

OUTPUT: max 2.5 rms @ 600 ohms

RADIO: max 1.2 rms @ 2.5 K ohms

PHONES: 200 - 600 ohms (no electrostatic)

Semiconductor complement:

54 Transistors; 32 diodes, 4 silicon rectifiers, 1 CdS-cell

Remote control:

Fully electric for all operation functions.

Output Amplifiers:

Plug-in optional. 2 x8 watts continuous rms power, 2 x10 watts music power as per IHFM, 4-16 ohms, less than 1% distortion.

Power Supply:

Electronically stabilized.

Mains voltages:

110, 130, 150, 220,240, 250V / 50-60 Hz.

Power consumption:

70 ... 100 watts

Dimensions (Wooden Cabinet):

161/4" W x 141/8" H x 81/2" D. (Measurements include knobs but not reels.)

Weight (Approximately):

34 pounds (» 20 kg)

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