Audio interconnection board for
all Studer Revox B77
For this board, Revox calls the board Audio Interconnection PCB, there are the wildest names:
Back plan
- I don't like it at all, it's more something for industrial computers.
Motherboard
- I don't like that either, it's more of a computer thing.
Switchboard
or Switch board- yes, at least the rotary and toggle switches go on it.
Audioboard
- so are the other cards.
It took three attempts to position the switches correctly, get the rotation direction, and the assignments right. There was no template. A switch with 3 levels and 5 positions isn't available in any library. Standard rotary switches are available with 1 x 12, 2 x 6, 3 x 4, 4 x 3, or 6 x 2 positions, but not 3 x 5!
The purpose of the new audio connection board is:
the switching of the equalization of the speeds is done via relays, new gold-plated switching contacts of the rotary and toggle switchesnew plug contacts on the circuit boards
As a result you will receive:
a speed switch with optical and therefore wear-free scanningbrand new gold-plated switch contactsround, wide and 70µ thick conductor tracks.
Another advantage is:
no dropouts of the rotary and toggle switch contactsno dropouts of the plug contacts of the circuit boardsoptimized conductor routing through individual and freely positioned relays
Circuit diagram
Revox never provided a circuit diagram for the audio interconnection! The functions of the switches, connections, and displays are only sketchily indicated on the respective audio cards. The necessary connections to the plugs, switches, and so on had to be laboriously developed and tested..
the new circuit board
Everything here is dictated by the Revox B77. The positions of the toggle switches, the rotary switches, the positions of the circuit board contacts. As you can see, the circuit traces are very long. The 70 µm thickness and the width certainly can't hurt here. Even the circular routing doesn't cause any damage (apart from the visual aspect)!
rotary switch
The layout of t he rotary switches had to be redesigned. The rotary switches are universal, consisting of three levels with five contacts each. In the original, several contacts are designed as a single surface. This would require creating a new switch for each position. The spacing of the contact surfaces has remained roughly the same. This means you retain the popping sound, especially when switching between Mic Hi and Mic Low!
toggle switch
The layout of the toggle switches also had to be redesigned. However, this was easier than the layout of the rotary switches. The position of the holes is important. We want the circuit board to be interchangeable one-to-one, without having to remove the switches from the chassis. Only in exceptional cases do the switches need to be removed from the chassis and realigned.
speed
Not to be overlooked – the speed change is now optical and therefore wear-free. How many times has the Pertinax push rod of the slide switch broken? That problem no longer exists here.
Fork light barrier
The forked light barrier we use is mounted perpendicular to the circuit board. Everything fits perfectly; no additional adjustments are required! The driver of the push rod now switches the light barrier.
At Premium-Hifi we only use available components of outstanding quality.
the old switch
Not only is the switch highly prone to breakage, but the contacts are also exposed and easily soiled and oxidized. The position of the Revox switch contacts is already optimally designed. We couldn't optimize or improve much with the new layout. The only things that remain are the conductor routing, thickness, and width.
Replacing the audio connection board
Screws without end
Remove device
The four rear GLoosen the housing screws and carefully pull the tape machine forward out of the housing.
But be careful! Never place the device on its front side! Slowly pry the device out of the case—it works!
CAUTION! Unplug before opening!
115 Vac / 230 Vac can
fatalbe!
Shield sheet
Loosen and remove the shield plate with two screws
5 Remove audio cards
Now you can remove the five audio plug-in boards (from left: Oscillator, Record, Input, Reproduce, and Monitor). You can also take a few photos with your phone or number the circuit boards.
Remove circuit board
Once all connectors have been removed, only 12 small screws remain to be removed. Be careful when removing the circuit board. The circuit board is stuck to the old switch screw connections.
Here, too, it helps to take a few photos with your phone for documentation. It never hurts!
Also be careful with the slide switch. Even if we no longer need the switch, it doesn't have to break.
the new circuit board
The new circuit board should fit 1 to 1 and with a little pressure the switch mounts should fit into the holes of the new circuit board.
If the switches don't fit
then the front panel has to come off!
Sidebar
The side panels are attached with two screws each on the right and left. Before removing the side panel, you should unhook the springs from the front flap. Now remove the side panels and put the front flap away as well.
buttons
Pull off the knobs of the rotary switches and potentiometers and carefully remove the lower front panel. The toggle switches are a bit cumbersome, but you should be able to remove the front panel with some care.
Rotary or toggle switch
The rotary or toggle switches are each attached to the chassis with two screws. Slightly loosen the screws of the switch you want to adjust and slide the switch to the position that allows it to snap into the circuit board. Then retighten the screws moderately.
Danger!
When assembling, care must be taken that no Wire is clamped between the circuit board and the switch! Pinched wires cause poor or no contact between the switches and cause disgusting fault patterns.
The
new audio connection board in our shop
Here you will find the brand new audio connection board
the Revox B77 and Revox PR99
