quartz-stable speed control for all
Studer Revox B77 and PR99
It was the most difficult development of the Revox B77 circuit boards. Not only did the existing audio motor control achieve excellent synchronization values, but we never wanted to be worse than what was already available! We also had to generate an analog signal for the control system from a quartz clock as a digital signal. On the one hand, the control system had to be fast to maintain short latency, but on the other hand, it couldn't be too fast to avoid negatively affecting the synchronization values.
The purpose of the new speed control is:
Quartz-stable and temperature-independent speed
the variable speed, if available, remains usable.
As a result you will receive:
A state-of-the-art control system that operates with quartz precision using a 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 reconciliation required.
real plug & play
No drift due to temperature fluctuations
The warm-up phase can be omitted
You always have the right speed right from the start!
the new control
for Revox B77 and PR99
Four ICs are responsible for the Vari-Speed alone. Instead of six ICs like in the Revox A77, this one uses just ten ICs. We've moved the heat sink away from the bottom of the circuit board, allowing the heat to accumulate underneath. Both the heat sink and the power transistor are mounted on top, allowing heat to dissipate much more effectively.
Original Speed Control
The original speed control consists of two ICs and is not particularly temperature-stable. Both ICs are used in a similar form in our circuit. In addition, there are four additional ICs in the Revox A77 circuit and eight additional ICs in the Revox B77. The number of ICs is not a quality indicator, but rather a reflection of the enormous effort that went into making them!
hanging mounted
The speed controller is mounted suspended. Therefore, we repositioned the heat sink and power transistor, placing them at the top! This allows heat to escape upwards more easily and be dissipated with the thermals. The cooling surface is also larger, measuring 3 mm thick.
A few graphs
Play-Start 19 cm/s
We will not comment further on the graphs.
There's a single, brief overshoot at 19 cm/s. This overshoot doesn't affect the engine speed, so you won't hear the engine roar before it dies down again!
Play-Start 9,5 c m/s
The control is very fast—faster than the original. When the capstan speed control is engaged, the yellow sync LED indicates this.
You can also recognize the overshoot by the brief lighting of the sync LED.
Speed change
It looks good, but that doesn't mean anything! It won't help if we tell you that's the PLL1 and PLL4 signal.
Just this much, the speed control works very cleanly and very quickly and the accuracy is brilliant!
Replacing the tone motor control
real plug & play
Remove device
The four rear
Loosen the casing screws and carefully pull the casing forward and out of the case. But be careful! Never lay the device on its side, on its front! Slowly pry the device out of the case – it works!
CAUTION! Unplug before opening!
115 Vac / 230 Vac can
fatalbe!
Remove flat plug
For the speed control of the Revox B77 or PR99, only the three flat plugs P5 (sw), P4 (or) and P3 (ws, from outside to inside) of the Vari-Speed need to be removed.
Loosen screw
To replace the circuit board, you must completely remove the screw. 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 toward the connector panel and remove it.
the new circuit board
The new Premium Hifi speed control can now be installed in the position of the old circuit board. The cooling bracket should snap into place against the chassis, thus maintaining as much contact with the chassis as possible. Now screw in the new speed control and plug in the three Vari-Speed flat connectors as shown.
Flat plug
Only the three flat plugs of the Varispeed connection need to be plugged in.
From left to right: bl = 0 V, wh = ref signal and or = 12 V.
Two green LEDs indicate the presence of voltage 5 V and 12 V. A yellow LED indicates the speed setting.
It couldn't be easier! You don't have to send in the old capstan control or tone motor control, or attach an additional metal housing with Velcro fasteners, and make various connections.
Just swap the circuit board, reconnect three connectors - that's it!
Real 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
Sound motor control of the Revox B77 and PR99
