# Expression jack for Parentheses octave



## JMan (Jan 7, 2022)

Hi Everyone,

This is my first post here.  I've been building studio gear for several years, but recently got a hankering for some variety and decided to build a few pedals.  Everything has been great so far, and I've completed several nicely-functioning boxes!  It's pleasant to work with voltages that aren't trying to kill you.

I'm about to start a Parentheses fuzz.  I feel pretty comfortable with the schematic, but I'm curious about adding in an expression jack for the octave control.  Will the attached diagram from the PedalPCB wiki function correctly for this application?  And is there a specific type of isolated TRS jack that I should use (are there even different types -- like switching vs non-switching)? 

Apologies for these very basic questions.  Since my experience is with rack gear, I've never even thought about an expression pedal and I feel oddly unsure of what I'm doing.

Thanks in advance!

EDIT: Also, I think I probably should have asked this in the "Modifications" section, but I'm new to the forum and haven't quite gotten the lay of the land yet.  If mods want to move this, by all means please do.


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## JMan (Jan 7, 2022)

Well, after a bit more searching around, I found a thread that I hadn't come across before where this was discussed, and it seems that it is pretty straightforward.  

I'm thinking that something like this is an appropriate jack to use.  

I'd be happy if anyone wanted to confirm, but if I don't hear anything, I'll just try it out and see what happens!


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## Nostradoomus (Jan 7, 2022)

Yeah as long as it’s a switching jack like that one you'll be fine. Making sure you have a 50k expression pedal is more of a problem haha.


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## JMan (Jan 7, 2022)

Yeah, I actually have no idea how to account for that.  Before today, I didn't even consider that different expression pedals had different impedances.  I'm taking a crash course in "obvious stuff you should have realized, dummy."  😅


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## jmsfcx (Jan 11, 2022)

just a heads up, doing an expression jack with a blend type circuit for the octave effect in this might result in noise if your expression pedal has a metal casing. the signal with be on the sleeve of the jack no matter what if you wire it traditionally.


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## JMan (Jan 12, 2022)

jmsfcx said:


> just a heads up, doing an expression jack with a blend type circuit for the octave effect in this might result in noise if your expression pedal has a metal casing. the signal with be on the sleeve of the jack no matter what if you wire it traditionally.


Interesting.  Is this because it would be interacting with the audio path directly as opposed to a control voltage or something like that?

I'm now going down the expression pedal rabbit hole.  It gets relatively heady considering how simple it seems at first blush!


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## jmsfcx (Jan 14, 2022)

JMan said:


> Interesting.  Is this because it would be interacting with the audio path directly as opposed to a control voltage or something like that?
> 
> I'm now going down the expression pedal rabbit hole.  It gets relatively heady considering how simple it seems at first blush!


sorry for the late reply. yes exactly right. expression control is very simple when it’s just controlling a main voltage (0-3.3v, 0-5v etc), that usually doesn’t need a specific potentiometer resistance value. but when it comes to controlling signal and does need a specific resistance value range to sound right… it can be a challenge!


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## JMan (Jan 14, 2022)

I see that EQD has implemented this expression jack on their more recent version of the Life Pedal.  I wonder how they’ve gone about this.  The only gut shots I can find online are of the older version with no expression jack.  Wish I had one on hand to open up.


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