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
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.
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!
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.
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!
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.
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!
Replacement of the speed control
real plug & play
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!
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.
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.
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.
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's that easy! You don't have to send in the old drive controller anywhere or attach an additional metal housing with Velcro.
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
Thomas Schröder
Schottjer Straße 30
26529 Upgant-Schott
Germany
Schottjer Straße 30
26529 Upgant-Schott
Germany
49 4934 - 80 44 39
info@revox-online.de