Author Topic: Volume Pedal as an expression control  (Read 648 times)

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Kipper4

Volume Pedal as an expression control
« on: August 23, 2016, 11:30:53 AM »
Heres the deal.
I was wondering if one could use a "std" volume pedal as an expression pedal for diy stomp boxes?
After all its just a pot in a box right?
I have used my volume pedal as an expression pedal before with my little Zoom 505 (old school I know) with a Y cable.

So If i wanted to use the volume pedal as an expression pedal such as part of a resistive divider to vary the speed of an lfo could it be done?
Ergo; Phaser speed? Tremolo Speed?

Btw what value of pot is standard in a volume pedal. If there is a standard.
If not then I guess a 4 poles switch with various sized R on the lfo would do the trick.
Cheer
Rich

Jellybean dodging since 2012.
Smoke me a Kipper. I'll be back for breakfast.

Kipper4

Re: Volume Pedal as an expression control
« Reply #1 on: August 23, 2016, 01:07:04 PM »
I just stuck the meter on the in's, outs
no variable resistances on the ins
but a swing from 18k to 110k on the outputs.
At least I know what i have to work with now.

Same for anyone elses please ?
Jellybean dodging since 2012.
Smoke me a Kipper. I'll be back for breakfast.

Mark Hammer

Re: Volume Pedal as an expression control
« Reply #2 on: August 23, 2016, 01:12:13 PM »
Depends on the make.

F'rinstance, the Line 6 standard is simply a 0-10k variable resistance to ground.  In my old MXR 113 Digital Delay, it was a 50k resistance to ground.  In other cases, the expression-pedal input assumes that you'll be dividing down a specific voltage.  Source Audio pedals use 3.3V, while others might use 9v or 5V divided down.  The voltage that gets divided down might come from the pedal itself, requiring a TRS jack and plug.  Where the expression pedal is presumed to come with its own power, there might be a 9V battery in the expression pedal, with a 5V three-pin regulator to provide a stable 0-5V variable control voltage.  It may use the pot in the controller as a 3-lug voltage divider, but only a mono hot/ground plug and jack are required at the effect pedal jack.

I have no idea what's most common.  Of course, if it's DIY then the choice is yours.

FWIW, once I learned the Line 6 standard was a simple 0-10k, I wired up a photocell to the expression jack input, taped it to the top of my guitar near the volume pot, and "played it" with my pinky.

anotherjim

Re: Volume Pedal as an expression control
« Reply #3 on: August 23, 2016, 02:02:31 PM »
10k is the most common for the expression pedals meant for things like keyboards and other digital/midi gear. As they are providing a variable voltage, the pot value isn't too critical. The annoying thing that varies are different ways of wiring the TRS. Sleeve usually ground, but tip & ring can be either  +V or wiper. To work with a variety of expression pedals, it would be an idea to fit a DPDT slide switch to select which tip/ring type. Because the pot value can vary, it would be wise to use voltage control, or a buffer to to turn it into current control, in the effect.

Working with a guitar volume pedal instead with an in/out adapter cable might be a better approach.  The higher value of volume pots might better suit direct control of stompbox circuits, but only if it has a ground at one end. That said, you probably could get away with envelope/LFO (non audio) controls with the sleeve "live" and an isolated TRS socket. Of course, the TRS socket can be like the Cliff/Rean fitted with extra contacts that are made when the plug is out, so a panel control can still be used.

"So lets stay within the limit of sureness: lets consider the fuses you have available and lets see what you have to do to light them up..." Farfisa Partner 15 drum machine manual.

Kipper4

Re: Volume Pedal as an expression control
« Reply #4 on: August 23, 2016, 02:20:00 PM »
Thanks guys.
I just assumed all volume pedals are the same.
for clarity.
I have a passive 2 in 2 out guitar volume pedal (made in Korea) IIRC sold by JHS back in the 90's

I was thinking of using it (or rather its resistance) as one half of a resistive divider to vary the speed of an lfo.

Sorry for any confusion, I now realise you can get other sorts of volume pedals.
It never even occured to me you could get active ones.
let alone different jack pinouts.

I'll try to do a mock up of what i had in mind. This could lead to even more confusion though :)

Jellybean dodging since 2012.
Smoke me a Kipper. I'll be back for breakfast.