quartz-stable tone motor control for
Revox A77 MK I bis MK IV
The first new development for the Revox A77 circuit boards. Here, too, the focus was on ensuring that the quartz-controlled speed control exhibits virtually no temperature drift. It doesn't matter whether you start the A77 at -10°C or if it's been running for several hours at 30°C in the shade. The speed always remains the same! Added to this is the precision, which you can never adjust as precisely with a trimmer. The circuit is very similar to that of the Revox B77 and Revox PR99. Only the connections, the lack of Varispeed, and the layout 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 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 activated and the tone motor is running synchronously.
Another advantage is:
no drift due to temperature fluctuations
the warm-up phase can be omitted
You always have the right speed right from the start!
No reconciliation required.
for all Revox A77
It was very important to us to keep the connections in their original position. The Revox A77's speed control is mounted suspended. Two wires coming from the transformer must be soldered, otherwise this circuit board would also be "plug and play." Anyone who can open a Revox A77 can also install the quartz-stable tone motor control!
A77 IC-Version
The circuit was developed sometime in the early seventies of the last century - ingenious!
Okay, many connections are implemented with flat plugs, that's how it was back then. Nowadays, you can hardly find plugs and sockets with a 2.54 mm pitch.
A77 L-Version
The A77 had two completely different versions of the tone motor control. Here's the early version with a coil (L-version). Alignment is somewhat difficult due to the position of the circuit board and the twisting of the coil core. Later, the IC version followed, which is very similar to that of the B77 and PR99.
improved cooling
To prevent heat from accumulating beneath the circuit board, we at Premium-Hifi have provided 28 additional holes around the heat sink. They're just small details, but they show that we've put some thought into it! For us, this is a given! Of course, without weakening the circuit board!
hanging mounted
The sound motor controller is mounted suspended. Therefore, we added 28 additional holes to the circuit board around the heat sink. This allows the warm air to escape upwards. The heat sink is, let's just say, well-sized.
a few 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. However, the overshoot is still much smaller than the original—much smaller!
Yes, the control behavior is identical to the Revox B77
Play-Sart 9,5 cm/s
Nevertheless, the control is very fast, much faster than the original. When the 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
Looks good, but that doesn't mean anything!
It's no use if we tell you that this is the signal PLL1 and PLL4.
Just this much: the control works very cleanly and very quickly and the accuracy is brilliant!
Replacing the capstan control
Revox A77 MK I - MK IV
Remove housing
Loosen the four rear housing screws and unplug the dummy plug or remote control, as well as the power cable. Carefully pull the housing forward and out of the housing.
But be careful! The chassis can get quite jammed in the case! This requires a lot of patience! Never lay the device on its front!
ATTENTION! Even if you are forced to unplug the power cord, leave the plug unplugged afterward!
115 Vac / 230 Vac can
fatalbe!
Remove flat plug
The Revox A77 has many 2.8 mm flat connectors, all of which need to be removed. Here, too, it's okay to take a few photos of the connections with your phone! The new circuit board has the connections in roughly the same position. Additionally, two wires (black and blue) coming from the transformer need to be desoldered.
Unscrew
If only unscrewing the circuit board were as easy as everything else! It's certainly possible with a long flathead screwdriver with a shaft length of 150 mm or more. Still, the job is a bit fiddly, and some patience is required!
three screws
To hold the screws and prevent them from falling into the device, we use the good old Hirschmann clamp. This allows you to safely remove the screws from the Revox A77.
screw tight
The mounting position remains unchanged. It has to fit the Revox A77 as well! Here, too, you can fit the Hirschmann clamp with a screw and washer and guide it to the hole, allowing you to easily tighten the screws. To do this, you'll need to turn the Revox A77 upside down.
the new Quartz Control
The positions of the screws and especially those of the flat plugs and the two transformer connections have remained roughly the same!
First snap, then release!
This means you can connect and operate the new circuit board using the old pinout. The manual replacement is quicker than we can describe here. No calibration is required. You'll always be as close to the target speed as with any other board!
old and new
The new cruise control is a full
30% smaller than the original board.
30% smaller than the original board.
Both tone 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
