"Multiplying" an expression pedal

eleanor296 · July 08, 2009, 11:39:17 PM

hey guys,
got a quickie here:
How would I go about dividing an expression pedal's output into two "pieces"?
I know I could just do a dual pot, but that'd be one more cable having to go aaaaalll the way to my rack.
I'm just trying to see if anyone's done something along the lines, there's probably an obvious answer, but it's kinda late over here.

If not, I'll play around with some LDR's tomorrow.

Andy

EW57 · July 09, 2009, 12:33:56 PM

Quote from: eleanor296 on July 08, 2009, 11:39:17 PM
How would I go about dividing an expression pedal's output into two "pieces"?

Could you reprase your intentions?
Is this something that could be done with a dual pot & a stereo (TRS) cable?

eleanor296 · July 10, 2009, 02:38:49 PM

hmm... haven't thought about the stereo cable yet.

Basically, I take an expression pedal, and would like for the "resistance signal" to be "cloned", so that I could feed it to two different rack units.

Does that make more sense?
Sorry, English isn't my native language.

Andy

MikeH · July 10, 2009, 02:50:04 PM

So you want to use the same expression pedal to manipulate 2 exact units in the same way?

If that's the case, you can just replace the pot with a dual ganged pot of the same value/type, and add another jack and run the 2 cables, which you can bundle together.

ppatchmods · July 10, 2009, 03:01:56 PM

would a split cable work in this instance? 1/4" stereo to 2 1/4" stereo cables??

jacobyjd · July 10, 2009, 03:07:01 PM

LDR all the way. Drive 2 LEDs, maybe use a trimpot to compensate for tolerances.

MikeH · July 10, 2009, 03:34:26 PM

Quote from: ppatchmods on July 10, 2009, 03:01:56 PM
would a split cable work in this instance? 1/4" stereo to 2 1/4" stereo cables??

Depends on how the expression pedal is wired. If it's a 'resistance to ground' type thing, then yes. One stereo jack works, and you can fasion a stereo to 2 mono cable setup. Otherwise you have to use 2 jacks and 2 cables.

MarcoMike · July 10, 2009, 03:39:58 PM

that needs energy... 2 pots don't...

I had a stereo pot wired as voltage divider in my pedal and that's cool cos you can take the voltage from the pot's wiper if you need a CV... use an ldr if you need R (or just half the pot...I don't know..)
now I have 4 devices connected together so they can share envelope, LFO, vanishingpoint, pedal, S&H as contro. i used the ground/CVin/CVout scheme for all of them, for sake of simplicity...

sean k · July 10, 2009, 06:09:32 PM

Um, I don't see why you would even need two pots 'cause they'll be tracking the same anyways and you'd need to double each wipers resistance so the load is the same which would change the output resistances. Why not just use the one pot and just split the outputs.

I would think the only concern really is ground loops running cables between boxes so the concern for me would be isolation issues.

eleanor296 · July 10, 2009, 09:50:50 PM

So I could just split the output?
I don't mind it needing power, but I really don't want yet another cable, that's my concern.

MarcoMike · July 11, 2009, 09:44:15 AM

not sure you can do that... it depends on the devices you're connecting the expression pedal to...

eleanor296 · July 11, 2009, 06:42:06 PM

It's two Digitech units... a GSP1101 and a DHP-33. Both digital, both can be calibrated.

Andy

Taylor · July 11, 2009, 07:02:49 PM

I would be careful doing that - you can kill equipment that way. The reason is that you're connecting the 2 different circuits together with a resistor. There may be some kind of isolation in the units, but who knows? Not worth maybe blowing your stuff up in my opinion. I have killed a couple of DIY effects this way.

eleanor296 · July 11, 2009, 07:49:31 PM

hmmm... good point.
This sucks.

Taylor · July 11, 2009, 09:58:39 PM

How about this, a synthesis of the ideas already suggested:

Use the single pot in the exp. pedal. Run it into your rack (one cable!), where you'll build a little box containing an LED and however many LDRs you want. The exp pot will control the voltage going to the LED, which will shine on 2 or more LDRs, which will be wired to jacks on the box. This way, one cable going to your rack, but as many expression outs as you want (or as many LDRs as you can fit around an LED). All the other cables will be right there in your rack.

eleanor296 · July 12, 2009, 10:11:30 AM

And due to the LDRs, they'll effectively be isolated from each other too.
Great idea, thanks.
I think I'm out of those though... where's that mouser catalog?

eleanor296 · July 14, 2009, 11:00:50 PM

Found something in this thread:
http://www.diystompboxes.com/smfforum/index.php?topic=73786.20

Looks promising.

Also... I had another idea, that seems way simpler:
I probably won't be using the expression pedal for both units at once, at least I can't think of any application of that right now,
so I figured since I have a function switcher in my rack I could use that to change the state of a relay in order to either route the expression pedal to unit 1 or unit 2.

How's that sound? Any complications I'd run into?

Andy

thebarkpetition · August 25, 2009, 05:16:32 PM

I've been wondering the same thing. I'd like to fill a project box with a bunch of 1/4" inputs and a rotary switch, and one 1/4" out to an expression pedal, and then just switch the box so that it connects to any of the outs, one at a time - like a simple (manual) expression pedal switcher. Anyone tried this?

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"Multiplying" an expression pedal