CS-80 Calibration Part 7: Ring Modulator

PRA Board with Shield

The Ring Modulator Board (PRA) is the last board at the right side on the rail and a little tricky to get out due to the wire harness being in the way. It's furthermore the only board that is covered with a tinfoil shield. To remove it, the rack ears have to be unscrewed.

During the adjustment procedure the ring modulator suddenly stopped modulating in between. As it turned out the IG00150 "half"-died.

"Half"-died in the sense that all other pins of were working as intended (saw-wave output works fine), just the sine-wave pin showed no activity anymore. I'm not sure if I slipped by accident somewhere along adjusting or if it just died on its own.

PRA Board

Fortunately, the Tremolo/Chorus Board has two IG00150. As I don't really like how the chorus or tremolo changes the sound color, I decided to steal one of those until I see some IG00150s showing up somewhere. After some thinking I decided to remove the second IG00150 as well and store it in my drawer as a spare part. If I don't use the feature and I can remove it, then it's better to have rare custom chips stored somewhere else instead of wasting them for nothing.

The adjustment itself slowed me down a little. Setting the attack time was a little fiddly because with every note hit the slope started at another point. Setting the speed took some time too, but went smooth at least.

For the ringmod balance I have been pingpong-switching my scope between GND and DC and moved the line until it matched with GND. Also an easy task.

Some caution is required when working on that board, there is a GND line uncovered going into terminal E and I apparently managed to short circuit it with VL1 by accident:

E terminal unshielded

Continue to Part 8: Tremolo/Chorus