quartz stable capstan speed for
Revox A77 MK I to MK IV
The first new development of the Revox A77 circuit boards. Here, too, the focus was on the fact that the quartz-controlled speed control had hardly any temperature drift. It doesn't matter if you start the A77 at - 10 °C or if the A77 has been running in the shade for a few hours at 30 °C. The speed always stays the same! Added to this is the accuracy that you can never set so precisely with a trimmer. The circuit is very similar to that of the Revox B77, Revox PR99. Only the connections, the missing varispeed and the arrangement of the circuit board have changed!
The purpose of the new speed control is:
Quartz-stable and temperature-independent speed without adjustment
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 sound motor is running synchronously.
Another advantage is:
no drift with temperature fluctuations
the warm-up phase can be omitted
You have the right speed immediately and always - right from the start!
No matching required.
for all Revox A77
It was very important to us to leave the connections in the old position. The speed control of the Revox A77 is mounted hanging. Two wires coming from the transformer must be soldered, otherwise this circuit board would also be "Plug and Play". If you can open a Revox A77, you can also install the quartz-stable sound motor control!
A77 IC-Version
The circuit was developed sometime in the early seventies of the last century - brilliant!
Well, many connections are made with flat plugs, that's how it was back then. It's hard to find 2.54mm pitch plugs and sockets these days.
A77 L-Version
There were two totally different versions of the sound motor control on the A77. Here the early version with coil (L version). The alignment is somewhat more difficult due to the position of the circuit board and the twisting of the coil core. The IC version followed later, which is very similar to that of the B77 and PR99.
improved cooling
So that the heat does not accumulate under the circuit board, we at revox-online have provided 28 additional holes around the heat sink. It's just little things, but that's how you know who cares! For us something like that is a matter of course! Of course without weakening the circuit board!
hanging mounted
The sound motor control is mounted hanging. That's why we added 28 additional holes to the circuit board around the heatsink. This allows the warm air to escape upwards. The heatsink is, shall we say, well dimensioned.
some graphs
Play-Start 19 cm/s
We will not comment further on the graphs.
At 19 cm/s there is a larger overshoot than at 9.5 cm/s. But the overshoot is still a lot smaller than the original, a lot!
Yes, the control behavior is identical to the Revox B77
Play-Sart 9,5 cm/s
Nevertheless, the regulation is very fast and much faster than the original. If the control is locked, this is indicated 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 control works very cleanly and very quickly and the accuracy is awesome!
Replacing the capstan control
Revox A77 MK I - MK IV
Remove device
Loosen the four rear housing screws and remove the dummy plug or the remote control and the power cable. Carefully pull the housing forward out of the housing.
But beware! The chassis can get stuck in the case! You need a lot of patience here! However, never lay the device on its front!
DANGER! Even if you are forced to unplug the power cord. Don't plug in after that either!
115 Vac / 230 Vac can
deadly
be!
Pull off the flat plug
The Revox A77 has many 2.8 mm flat connectors that all have to be unplugged. Again, it's not bad if you take a few photos of the connections with your cell phone! The new board has the connectors in roughly the same position. In addition, 2 lines (black and white) coming from the transformer must be unsoldered.
Unscrew
If only unscrewing the circuit board was as easy as everything else! A long slotted screwdriver with a shank length of 150 mm or more will do. Nevertheless, the work is a little tricky and a little patience is required!
three screws
In order to hold the screw and to prevent the screws and toothed washers from falling into the device, we abuse the good old Hirschmann clamp. This allows you to safely remove the screws from the Revox A77.
screw tight
The position of the attachment is unchanged. Must also fit on the Revox A77! Here, too, you can equip the Hirschmann clamp with a screw and washer and guide it to the hole so that you can easily screw on the screws. For this work you have to turn the Revox A77 upside down.
the new quartz control
The positions of the screws and above all the flat plugs and the two transformer connections have remained about the same!
Snap first, then solve!
You can therefore use the old pin assignment to connect and operate the new circuit board. The exchange is faster by hand than we can describe here. A comparison is not required. You are always more accurate to the target speed like with any other board!
old and new
The new cruise control is around whopping
30% smaller than the original circuit board.
30% smaller than the original circuit board.
Both sound motor controls are mounted hanging in the Revox A77.
The new quartz-stable tone motor control in our shop
Here you will find the brand new quartz stable
Sound motor control of the Revox A77
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