[sdiy] Building an expression pedal for MS20

[rsdio at audiobanshee.com]

Many synth foot pedals are already wired with the 1/4" stereo jack that Quincas is using. The voltage comes in on the Ring and Sleeve, is wired to the pot internally so that the wiper voltage comes out the Tip of the plug. (I may have Tip and Ring reversed). Basically, a pot is a 3-terminal passive device, and the 1/4" stereo jack offers all three terminals directly. There's nothing else in those pedals.

The only drawback of these passive pedals is that they don't provide voltage unless you feed it to them. But that's actually a benefit, because it means they're compatible with 10 V CV or 5 V CV by just sending a different voltage.

The box that Quincas built solves the only problem with the passive pedal by providing power.

I wouldn't be surprised if some modular company already has a module that takes power from the bus and has a 1/4" jack for the expression pedal, maybe with the attenuator that Quincas has on his custom box for extra control. I looked at Synthwerks because they have very similar modules, but I didn't see anything that would work with a standard, passive synth expression pedal. Maybe this is an opportunity for a new product?

Brian Willoughby
Sound Consulting


On Feb 25, 2015, at 6:31 AM, Quincas <quincas at gmail.com> wrote:
> An expression pedal is just a potentiometer controled by foot. I use one with my modular all the time. Basically I made a little box with a 9 v battery inside and two jacks. One stereo jack sends 9v to the pedal and receives the attenuated voltage back. That voltage goes through another pot in the box for range control then out the second jack to the modular. Normally I use it to control filter cutoff, lfo or delay speed, etc. fun easy diy project, have fun!
> 
>> On 25/02/2015, at 6:07, Jean Bender <lofideadbeat at gmail.com> wrote:
>> Well, for a musical project, i need to control some parameters from
>> the MS20 with an external processor, and that's would be really great
>> if it could be controlled by foot.. In order to play with the cv
>> inputs cutoff. It should really do the same as when you are manually
>> turning a pot..
>> A bit like the mod wheel, but for the foot..  An expression pedal like
>> should be great, but i would have to build in a lfo ? Or a vco ?
>> Would somebody have advices, ideas.. Maybe this kind of project already exist..