Cv control from volume or expression pedal.

[mills]

Sorry if this question is way too simple, but I put down my bass and soldering iron for about a decade and am starting to mess around with both again.

I was looking to make an expression style pedal into a cv controller as I have a handful of pedals that have cv inputs.  If possible i wanted to switch between 9v and 5v as some inputs are +/-9v and others are +/-5.

1) Should I be looking at a more advanced circuit than just a battery with a capacitor to the ground for smoothing then use the pot as a voltage divider (one side to 9v, the other to ground and wiper to output tip)?

2)for 4.5v it seems like I can switch an appropriate resister in series before the pot and it should work.

3) is there an ideal value for the pot?  I like ernie ball volume pedals so 25k or 250k is easiest.


Thanks for any help!

[Kevin Mitchell]

You've described pedals that use bipolar CV but suggested wiring the pot to a single supply. That will only get you half of the CV range - but really less once you realize that the foot pedal does not actually cover the typical 300° adjustment range of the pot, amongst other implications.

If I recall right, the ernie ball volume uses string to actuate the pot mechanism while most other wahs, volume and expressions pedals use a treadle (rack & pinion gears). The ernie ball pedal may be more difficult to modify. Go Moog EP3 as they can be super cheap used or snag a knockoff wah shell kit for DIY.

The pot will serve as a voltage divider. 10K to 100K would be common and appropriate. Anything lower may be prone to burn-out as a divider between the supply rails. But then you'll want to add supporting circuitry to make up the rest of the desired range and a switch solution for 5v to 9v oporation.
You'll also have to consider the power input. I would suggest +12v with a charge pump for the inverted supply. With +/-12v you are not as limited with choices of opamps for your supporting circuitry (rail-rail specifically).

Welcome back. Let us know if you have any questions and we'll help you figure it out 

[Transistor-Transistor]

I've repaired an ernie ball volume pedal for a friend and replacing the string was the 2nd most frustrating thing I've ever done

[mills]

You've described pedals that use bipolar CV but suggested wiring the pot to a single supply. That will only get you half of the CV range - but really less once you realize that the foot pedal does not actually cover the typical 300° adjustment range of the pot, amongst other implications.

If I recall right, the ernie ball volume uses string to actuate the pot mechanism while most other wahs, volume and expressions pedals use a treadle (rack & pinion gears). The ernie ball pedal may be more difficult to modify. Go Moog EP3 as they can be super cheap used or snag a knockoff wah shell kit for DIY.

The pot will serve as a voltage divider. 10K to 100K would be common and appropriate. Anything lower may be prone to burn-out as a divider between the supply rails. But then you'll want to add supporting circuitry to make up the rest of the desired range and a switch solution for 5v to 9v oporation.
You'll also have to consider the power input. I would suggest +12v with a charge pump for the inverted supply. With +/-12v you are not as limited with choices of opamps for your supporting circuitry (rail-rail specifically).

Welcome back. Let us know if you have any questions and we'll help you figure it out 

Thanks for taking the time to reply!  I'm mostly OK with skipping the bipolar control.  I had felt like figuring out roughly where zero was with my foot while playing would be a pain.  I thought about cramming a charge pump into an existing pedal, but it seemed like it might be fiddly with all the parts in a tight space. A wah shell is probably a better plan if I go that route.

And I agree about the atring.  Super frustrating to change, but I liked the feeling of tension working the pedal.