Building an expression pedal with variable resistance.

[ihattwick]

So I have a boss EV5 that I have modded to control two different pedals. The way I have it set, there is a switch that determines which pedal is controlled by the rocker, and the other pedal is controlled with a momentary switch going from 0-25k. However, I recently bought a zoom G2 and was distressed to find that it's expresssion pedal wants to be a 250k pot, not sure whether its audio of linear taper yet. Is there a way to have a 10k pot remotely control a 250k pot? I was thinking of something like craig andertones volume pedal descratcher.

Also, I was wondering if there is a way to have the remotely controlled pot keep its current value when I switch the pedal to control a different unit.  I don't know if that makes sense!

[Jobet]

Hmm...

anyway, maybe not spot on but you might want to try what I'd been planning to do with my zoom G2.

Find a defective Behringer Hellbabe. Cut out all other circuitry to it, then power up the sweep LED. Wire the LDR of the sweet slot to a jack and plug that into your Zoom unit

Or maybe you can get creative and find a way to incorporate that LED-slot-LDR system into your EVH so you will get an independent variable resistance. You won't need to worry about the taper either because you can adjust that using the shape of the light slot

Just a thought to toss around.

[joegagan]

i am interested in the mechanics of the hellbabe opto circuitry. does anyone have one , or has anyone dissected it ?

[Jobet]

I have, Joe.

The sweep and bypass mechanism is  a knock off of the Morley Bad Horsie 2. Two led-ldr pairs, the first one turns the device on and off (bypass-effect) and the other controls the sweep. As you step on the rocker, a plastic insert with slots in them let the light from the LEDs go to the LDRs in graduated degrees.

It would have been a great pedal had Behringer just refined it a teenie weenie bit more. Anyway, I've modified my Hellbabe by cutting the sweep notch to make it more responsive, converting it to true bypass (you have to step on it at toe down to activate it just like a normal wah)  and inserting an organicore scalarizer in the effect signal path to make it sound warmer and modify the straight-cut linear tone that it used to have.

[ihattwick]

Wow, jobet- I guess I'm not 100% sure how that would work- I'm assuming that LDR's refer to optically controlled resistors. In this case, you'd have to have an LDR with the right ratings to send out as a control signal, which is a little bit different than I was looking for. But I guess I could have multiple LDR's for different resistance ratings, which would be workable. And the hellbaby sure is cheap! Do you leave the springs in the pedal?

[Jobet]

Yeah. I left the spring on it because when I removed it, the light plastic rocker became difficult to control. The resistance from the spring is good.

If I remember correctly again...the Zoom G2 is only looking for a 2 -legged resistance change, so from short circuit to its rated maximum should pass through 250k or whatever zoom needs. That's fuzzy logic thinking though, and there's no substitute for trying it out.

I was about to do this myself, but a cheap Zoom FP02 pedal is coming my way tomorrow. So I guess I won't have to touch my hellbabe for now

[ihattwick]

I thought the zoom needed 250k as well, and even ordered a few 250k pots to try out. Turns out it needs 100k- I have a rolls volume pedal, POS but small, that works ok. I'm going to try and put in a momentary switch on the top of the pedal for tap tempo as well- we'll see how that works out.

As far as finding a way to control pedals wanting 10k and 100k expression values from the same controller pedal, no luck- guess I'm gonna have to have two exp. pedals. Good for the control possibilities, bad for the floor real estate. . .