quartz stable capstan control for


Revox B77 and PR99
It was the most difficult development of the Revox B77 circuit boards. Not only that the existing speed control achieves excellent synchronization values. We never want to be worse than what already exists! Also to generate an analog signal for the control from a quartz clock as a digital signal. On the one hand, the control should be fast in order to maintain short waiting times, on the other hand, the control must not be too fast, so that the control does not have a negative effect on the synchronization values. The inertia of the motor also plays a role.
The purpose of the new speed control is:
Quartz stable and temperature independent speed
the variable speed, if present, remains usable.
As a result you will get:
A state-of-the-art controller that works with a quartz-precise tachometer signal of 800 Hz or 1600 Hz.
An LED indicates when the control is active and the motor is running synchronously.
Another advantage is:
No matching required.
real plug & play
No drift with temperature fluctuations
The warm-up phase can be omitted
You have the right speed immediately and always - right from the start!
the new control
quarzstabile Tonmotorsteuerung Revox B77, Revox PR99 von revox-online
quarzgeregelte Tonmotorsteuerung für alle Revox B77 und PR99 von revox-online

for Revox B77 and PR99

4 ICs are responsible for the Vari-Speed alone. Instead of 6 ICs as in the Revox A77, 10 ICs are installed here. We no longer installed the heat sink below the circuit board so that the heat can accumulate under the circuit board. Both the heatsink and the power transistor are top mounted and, like heat, can dissipate much better.
quarzstabile Tonmotorsteuerung B77, PR99 revox-online

Original Speed Control

The original tone motor control consists of 2 ICs and is not particularly temperature stable. Both ICs can be found in our circuit in a similar form. In addition, another 4 ICs are added to the circuit of the Revox A77 and another 8 ICs to the Revox B77. The number of ICs is not a quality feature, but only reflects the enormous effort that has to be made!
Revox B77 Speed Control, Tonmotorstuerung, revox-online
alte Capstanregelung Revox B77, PR99, revox-online
B-Seite Tonmotorsteuerung Revox B77, Revox PR99 von revox-online
die Tonmotorsteuerung wird kopfüber montiert, revox-online

hanging mounted


The tone motor control is suspended. So we changed the position of the heatsink and the power transistor and put it on top! This allows the heat to escape better upwards and be dissipated with the thermals. The cooling surface is also larger and 3 mm thick.
die Oberseite der neuen Tonmotorsteuerung, revox-online
A few graphs

Play-Start 19 cm/s


We will not comment further on the graphs.
At 19 cm/s there is a single short overshoot. The overshoot is not noticeable in the speed. So you won't hear the engine roar and then drop out again!
Signal bei 19 cm/s Tonmotorsteuerung von revox-online
Meßsignale der neuen Tonmotorsteuerung Revox B77, PR99, revox-online
Meßsignale bei 9,5 cm/s der neuen Tonmotorsteuerung Revox B77, PR99, revox-online
Meßsignale bei 9,5 cm/s Tonmotorsteuerung Revox B77, PR99, revox-online

 Play-Sart 9,5 c m/s


The regulation very fast - faster than the original. If the tone motor control is engaged, this is indicated to you by the yellow sync LED.
You can also recognize the overshoot by the brief flashing of the sync LED.
Signal bei 9,5 cm/s, Tonmotorsteuerung von revox-online

speed change


Looks good, but that doesn't tell you anything! It is also of no use if we tell you that this is the signal PLL1 and PLL4.
Only so much, the sound motor control works very cleanly and very quickly and the accuracy is awesome!
Meßsignale, Geschwindigkeitsänderung  der neuen Tonmotorsteuerung Revox B77, PR99, revox-online
Replacement of the speed control

real plug & play


Gehäuse öffnen Revox B77, PR99, revox-online

Remove device

The four rear GLoosen the housing screws and carefully pull the housing forwards out of the housing. But beware! Never place the device on its front side! Slowly lever the device out of the housing - it works!

DANGER! Pull out the mains plug before opening!
115 Vac / 230 Vac can deadlybe!
Flachstecker der Speedcontrol abziehen, revox-online

Pull off the flat plug


With the capstan motor control of the Revox B77 or Revox PR99, only the three flat plugs P5 (black), P4 (or) and P3 (white, from outside to inside) of the Vari-Speed have to be removed.
Revox B77 Tonmotorsteuerung  Varispeed-Anschlüsse, revox-online
Tonmotorsteuerung mit nur eine Schraube befestigt, revox-online
Ausbau Tonmotorregelung Revox B77, revox-online

loosen a screw

To replace the circuit board, you must remove the screw completely. For technical reasons, the new Speed Control will no longer have an open slot like the original! You can pull the old circuit board to the right towards the connector panel and remove it.
die neue Tonmotorsteuerung, quarzstabil, hochgenau, revox-online

the new circuit board

The new revox-online audio motor control can now be fitted in the position of the old circuit board. The cooling bracket should snap in towards the chassis and thus maintain as much contact with the chassis as possible. Now screw on the new Speed Control and plug in the three flat plugs of the Vari-Speed according to the plan.

Einbau Tonmotorsteuerung Revox B77, revox-online
die quarzstabile Tonmotorsteuerung in der Revox B77 eingebaut, revox-online
eingebaute quarzstabile Tonmotorsteuerung Revox B77, revox-online

flat plug

Only the three flat plugs of the Varispeed connection have to be plugged in.
From left to right: sw = 0V, ws = Ref signal and or = 12V.
Two green LEDs indicate the presence of 5 V and 12 V voltage. A yellow LED indicates the locking of the speed.

It couldn't be simpler! You don't have to send the old capstan control, speed control anywhere or glue in an additional metal housing with Velcro and make various connections. 

Just swap the circuit board, reconnect three plug connections - that's it!

True plug and play

After studying the installation instructions, the conversion should take less than 5 minutes!

The new quartz-stable speed control in our shop

Here you will find the brand new quartz stable
speed control of the Revox B77 and PR99
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