Expression pedal distribution/guitar pedal + modular control integration design ideas/inspiration/etc

Just want to preface this post by saying that I’m most interested in exploring the creative approaches to using expression inputs I have access to in the music I’m making–so feel free to post about how you’re currently doing that, even if it doesn’t have anything to do with this mockup or idea. Happy to change the title/goal of this topic if this turns into a fruitful discussion of what people are already doing!


Wanted to share an idea I’m working on (feedback/suggestion for stuff already out there/etc. very appreciated!) figuring out that sort of revolves around solving two problems:

  • I have one expression pedal and many pedals that have an expression input on my board. It’s been my experience that recabling pedals is an annoying experience due to the fact jacks are usually a tight squeeze around other pedals/the board’s frame. I think the experience would be better (and more conducive to experimentation) if all expression ins were always connected and switchable via some sort of interface.
  • I have been wanting to experiment with connecting my eurorack modular and pedal system in more sophisticated ways than just audio signal flowing between them. I’m not sure of the best UX for this “bridge”–the module I mocked up is one example of such.

My thoughts (and totally just thoughts at this point) are revolving around building an I/O board that could be placed in some sort of optimized way to elegantly cable all expression in equipped pedals, connected (via DB25) to some sort of ergonomic interface(s) for manually manipulating those signals and where they are going to.

If it doesn’t make sense from the mockup, my thought was that the pedal based interface could “slot” into the base and the whole unit would be a rectangular prism that could sit on top of the board like other “utilities” (thinking along the lines of saturnworks stuff…but maybe this is sort of gimmicky/unfeasible in terms of actually building.

An addendum–the switches on those interfaces may need to be 3-way and include a “mute”.

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Interesting ideas here!
One thing that I’m not sure I understood correctly : you’d like to have both an attenuator and an attenuverter per channel?
If this is so, why is that?

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Thanks!

My thoughts were that the attenuverter would provide an offset voltage, similar to the design of some VCAs.

That being said, this might not be as necessary or useful for the pedal interface, especially if it was attached on the board. A knob on the pedal being controlled itself can act as a sort of offset.

As a side note now that I’m thinking about it, the only things that require power (on the pedal interface side of things) would be the offset voltage generation and LED signal indicator. The design could probably be made completely passive if you removed those two elements from the channels.

Looks like an interesting idea. In my opinion the attenuators etc are not necessary since sort of thing can usually be handled on the device itself. A quick way to select the destination of the expression pedal, preferably with the foot, would be the most important thing for me.

One thing to consider is that some devices may have a default connection inside the jack that’s broken once a plug is inserted. You would probably need to account for that regardless of if you use switching or an attenuator.

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My thoughts with the attenuators was kinda like creating a “meta” control signal where each pedal is reacting to the sweep differently–along the lines of the Octatrack crossfader. Definitely rethinking the offset pot at this point though.

A quick way to select the destination of the expression pedal, preferably with the foot, would be the most important thing for me.

A traditional looper design would work for this if it had TRS jacks I think. You would just need some way to mult out from the expression pedal into the in of each channel of the looper. The other piece to figure out would be the switching–I think most loopers are set up so each channel is independently off and on. I’m not sure if there’s something out there that would allow only one channel to be on at a time (thus switching with one press instead of having to do two, if that’d be important to you).

One thing to consider is that some devices may have a default connection inside the jack that’s broken once a plug is inserted. You would probably need to account for that regardless of if you use switching or an attenuator.

Good point. Do you happen to know if these sorts of “detect presence of Jack” circuits could be “spoofed”? I’m assuming this functionality is achieved by somehow measuring voltage and not physically detecting the presence of the jack, at least that’s what I think I’ve read in terms of how it works with the MI Rings and Just Friends run jack.

I think it’s more the fact that it probably wouldn’t even work properly if it wasn’t just switched to one channel. A lot of expression pedal inputs don’t work like synth CV. They just use the expression pedal as part of a voltage divider, they send voltage in on one end and get another voltage out the other send. https://www.strymon.net/strymon-tech-corner-1-anatomy-of-an-expression-pedal/ covers this pretty well. If you had the pedal connected to multiple destinations at once, it would cause a lot of problems.

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They don’t do anything fancy, just the voltage from the ring of the jack is connected to the trip by default. Some devices have them disconnected so the default is 0, but some have them connected so the default is high (whatever the voltage may be, 5, 9, 12V).

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Thanks for the link. been hand waving off all the technical details and just focusing on the ux so far. Good to be pointed in the direction of what’s feasible.

I also found this, which seems to cover a lot of bases :https://missionengineering.com/shop-2/products/expression/multi-use-exp/expressionator/?v=3e8d115eb4b3

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After reading that Strymon article, I realized I was thinking about things backwards.

The signal is coming from the pedal to be modulated,
Not the expression pedal.

“Distributing” a control signal doesn’t make sense the way I was thinking about it. I’m curious if it is possible to take the signal emitted from one of the expression pedals (which in this scenario I’m assuming can be used as a sort of 5V “master source”) and then “copy” and “isolate” its use within each channel to send to all subsequent pedals. Each channel having its own voltage dividing circuit which somehow reacts to the voltage division being done with the expression pedal itself.

From what I can gather, the Mission controller is somehow using the voltage division of the expression pedal that is connected, taking a “snapshot” of the output voltage post-division, and then emitting CV signals from its 3 outputs to be used for control. Since the CV signals are being digitally generated they can process and transform the output signals in interesting ways.

Kind of. They are sampling the position of the expression pedal using an analog to digital converter. In CV mode they are generating a CV output, but in expression pedal mode they are controlling a digital potentiometer, which acts as a kind of virtual pedal.

Thanks for the clarification.

Also, I think I found something in production very close to my original design–the Copilot FX Broadband