I recently came into possession of a Jimi Hendrix JH1 wah with a failed potentiometer.
viewtopic.php?f=13&t=986
I've resurrected it and found it had a faulty switch. I swapped a new standard 3PDT switch in (it doesn't need 3 poles, but that's what I had), and found all sorts of flakeyness with the switching.
It tuned out that the toe bump stops were missing. Without toe stops, the treadle hits the switch very hard, and, interestingly, the rack that turns the pot hits the baseplate - the toe bump stops are what keep all the geometry correct.
After a lot of trial and error I was able to fabricate new bump stops, and adjust the switch so that:
- The rack doesn't bottom-out on the bottom plate.
- The switch switches with the "right" amount of pressure on the toe of the treadle - not so little that you accidentally turn the pedal on/off. This is achieved by setting things just right so the bumpers compress just enough.
This adjustment is really precise to make everything work properly.
The small round bump stops that are usually available at the hardware store
will not work - they aren't tall enough. The bump stops must be 4mm tall. Any shorter and the rack hits the plate, much taller and the switch can't be adjusted to be actuated.
The material for the bump stops is CRITICAL. Not so soft that it compresses too much and the rack bottoms out, but soft enough that it does compress just enough to allow the switch to activate.
Here are some pics, just in case anyone else has the same problem in the future.
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- Wah rack with notes.jpg (261.54 KiB) Viewed 13650 times
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- Wah bump stops with notes.jpg (94.64 KiB) Viewed 13650 times
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- Wah bump stops with notes material.jpg (221.31 KiB) Viewed 13650 times
