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Tapco 4400 Reverberation Machine Restoration

My friend Lorne brought me this late 70's Tapco Reverb unit with lot's of issues. My main concern (but not his) was that the faders felt like crunchy peanut butter. My instinct tells me if I replace these faders, most of the issues will be solved.


The problem - this is an unusual fader, and is not manufactured any more. There is no fader that matches the size and pin locations, and the faders are board-mounted, not panel-mounted, so a wire bodge-job is out the question.




These faders have three pins and are taller than most. They also do not accept a cap, the post is simply made of white plastic that the user can interface with. I went with the ambitious and likely over-kill method of designing a PCB that adapts a modern fader to a form factor the Tapco likes


I used Bourns PTA45 series faders (5K version) because they have a straight shaft, they're really short, and they are inexpensive. You will need 8 x 50K and 6 5K linear faders.






This worked quite well. Getting them perfectly straight is a little tricky. I also took the time to paint the shafts white. Also completely unnecessary.








The other issue common with the Tapco is the op-amps failing from power surges. These opamps are no longer manufactured, and they have a different pinout compared to modern quad opamps. I designed an adapter board to use two SOIC-8 opamps in it's place.




In the end, this wasn't necessary as all the op-amps in this unit are functional.






The square of matte paint was applied by the customer - I had no hand in it.

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