Expression Pedal Drive Pot

[chongmagic]

Just going through this in my mind.

Following this: http://wiki.pedalpcb.com/wiki/Expression_Control_Wiring

Let's say I wanted to add an expression input to the drive pot, and the drive pot is B100k while the expression pedal is 100k stereo, this should work fine correct? If the value of the drive pot was say B10k then there would be some issues? Just to make sure I am understanding, the expression pedal will play nice as long as the pot value is about the same?

 

[Robert]

It should, yes.... although I'm not terribly familiar with stereo expression pedals, so I suppose it depends on how the jack is wired?

And it'll generally "work" if the values are mismatched, but the expression control may or may not behave exactly like the pot in the pedal.

The other factor is whether or not your expression pedal is isolated from ground. Most are, but I've seen a few that aren't... (I have one that is not)

The reason this would be an issue is that Lug 1 of the expression pot goes to ground, and the pot in your pedal circuit might not.

 

[Chuck D. Bones]

Another thing to think about is the effect the cable has on circuit behavior. Any pedal with the DRIVE pot in the feedback loop (TS, for example) may very well go unstable or turn into a radio receiver if the DRIVE pot is located remotely. A better way to accomplish a remote DRIVE control is to switch in an LDR in place of the DRIVE pot, then use the Expression pedal to modulate the brightness of an LED shining on the LDR. A little more complicated, but solves a few problems: long wires hanging off of sensitive parts of the circuit, Expression pot resistance not the same as the pot being replaced. This is simple to do when the pot being replaced is wired as a variable resistor. When the pot is wired as a variable voltage divider (BMP Tone pot, for example), then we have to get a little more creative. But it's doable.

 

[chongmagic]

Probably the reason why it is not done very often.