DOD FX-17 wah volume: almost a ready made theremin CV controller

[Processaurus]

I had one of these apart today to repair the cv output, and the way it avoids a pot is really cool, unlike other pedals that use photo cells or hall effect sensors, it uses theremin technology to make a control voltage.  It has a metal piece attached to the rocker pedal that slides down on this circuit board and gets close to a big tapered copper trace, making a variable capacitor.  Without the rocker on there, I could get it to work by smooshing a finger on the circuit board, and see the voltage on the cv out rise and fall. 

The CV section is really simple, looks like a good place for someone interested in making a theremin CV controller to get in the ball park.  I've been interested in something like that built into a guitar since I saw the Zvex Drip guitars (with a built wah probe).  Heck, if you just stuck the whole DOD circuit board in a guitar you'd have it...

Thanks to Paul Marossy for drawing up the schematic, it helped with my repair too.

http://www.diyguitarist.com/DIYStompboxes/FX-17.htm

info on the trimpots
http://www.diystompboxes.com/smfforum/index.php?topic=43776.0

[Paul Perry (Frostwave)]

I can only assume somone owns (or owned) the patent for the led/ldr wah, because this DOD effort is completely barking mad.
Quite apart from anmything else, consider the noise floor using a led/ldr against a 3080!

[Paul Marossy]

You know, the DOD FX-17 is a very quiet design, too. I also love that it doesn't have a pot at all in it that can wear out and give you grief. I've got two of them, one is permanently on my pedalboard and the other one is a back up just in case. 

[O]

Great circuit indeed... my only wish? I wish I could find the plastic that goes in between the metal rocker and the copper trace

[Paul Marossy]

I wish I could find the plastic that goes in between the metal rocker and the copper trace

I have an answer for that. Find a drafting supply place around you or online that sells 2 mil Mylar drafting film. All you need is one 8.5x11 sheet of it and you'll have a lifetime supply of it. I might even have some lying around somewhere. Let me check on that.

EDIT: I found a piece of 1 mil Mylar that I think would work OK. Maybe you could even fold it in half and use two layers of it. In any case, it's pretty tough stuff. If you PM me your mailing address, I'll send you some.