# Stereo Parenthesis possible? (dual gang pots and other components needed)



## Illiac (Mar 23, 2022)

Hello,

I have 2 unpopulated Parenthesis PCBs and would like to know if it would be possible to wire them up as a stereo unit. I‘ve built quite a few kits, but have not ventured much into these type of mods. Can anyone give me any pointers on dual gang pot values and any other components that might be needed? I’ll sort the enclosure out later.

Thanks!


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## Dan M (Mar 23, 2022)

What is the purpose of the dual gang pot?


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## Illiac (Mar 23, 2022)

To control 2 Parenthesis boards from a single pot (dual wipers, 1 for each board)


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## Illiac (Mar 23, 2022)

Or could I simply double a normal pot value up and use that?


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## almondcity (Mar 25, 2022)

I've never heard of this being done but I don't see why it wouldn't work. Kind of a neat idea


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## Illiac (Mar 26, 2022)

Thx for the responses. I’ll check in with some other forums and report back with findings for anyone else looking to do something similar.


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## JamieJ (Mar 26, 2022)

You could use a TL072 as a buffered splitter to split the signal and then go to two parentheses. Hopefully the buffer wouldn’t interact badly with that pedal.

Something like this on veroboard:


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## Feral Feline (Mar 26, 2022)

JamieJ's got it, start with a spluffer or powered splitter of some kind so you don't degrade the signal from the get go.



You could go with fully independent control, and get some wild sounds by setting one board very differently than the other. However...

There will be some component tolerance drift. 

I would try to match values part for part from one board to the other: if RX is meant to be 390k and Board-A's RX measures at 388k, then I'd try to make sure Board-B's RX measured 388k as well. Time consuming I know, but at least with metal resistors you can get +/- 1% tolerance, or perhaps you could order military-spec and narrow it further — I've never ordered mil-spec.

I think the main problem will be drift within the pot-values themselves. Pots can have up to 20% drift, depending on the brand/spec. You could add some trimmers to points in the circuit to compensate for component drift. At least for resistance. Not sure what drift is in what capacitors.



DUAL-GANG
Dual-gang pots will simplify adjusting the stereo channels, but how close is the one gang to the other? You might have to buy a bunch of dual-gangs, crack open the pots and measure and match bits and then reassemble. Maybe you don't. Maybe the amount of component drift is negligible — I don't know, I've never tried building a stereo dirt pedal before. Now that you've thought of it, I want to try it even though I don't ever play in stereo.

Lastly...
Not sure I'd want to attempt a stereo dirt pedal using such a large and complex PCB as the Parentheses. More parts means more things to go wrong and more chance for drifting values. A stereo Bazz Fuss might be where I start (I've got a friend who sometimes plays in stereo, he can be my guinea-pig. 


The neat thing is, what have you got to loose? Nada. Build up the two boards and a splitter, hook up the dual-gangs and see if you can make it work. If it doesn't work, disconnect the dual-gangs you've got two Parentheses ready to go.


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## almondcity (Mar 26, 2022)

Yeah I would definitely try a simple pedal first. I would think that the slight difference in values due to the tolerances might make a cool variation in the two sides


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## Bricksnbeatles (Mar 26, 2022)

of course you wouldn't need to do a splitter on the input if you plan on building this with stereo ins as well. I've done some stereo builds, and dual gang pots are in fact where its at! you will occasionally get a poorly matched dual gang, but generally they seem to have tolerances more than tight enough for this stuff.


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## Illiac (Apr 6, 2022)

Thanks everyone! Got mostly everything ordered and will be breadboarding once it all arrives. Just need to sort the normalling for mono in/ stereo out.


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