Controlling a wah with expression pedal?

[iamjackslackof]

Hi all,

I had an idea for adding a wah pedal to a multiple pedals in the same box build. I could add an order switch to move it before and after a fuzz face, etc. The problem is controlling the wah without trying to stick everything in a wah enclosure. I was thinking that an expression pedal connecting to the main enclosure could work, but I'm fuzzy on expression outputs and how/if this can be done.

My idea is to use a TRS connection from a wah shell with only the usual wah pot in it to a stereo/TRS jack in the main pedal. Each of the 3 connections on the wah pot would connect to the wah circuit, but with essentially really long jumpers.

Is this feasible? Is there a better way? Am I totally wrong on how expression/TRS works? Would the long-ass jumpers pick up lots of noise? Feel free to tell me how wrong I am below!

 

[DGWVI]

Should work just fine. I've used this diagram for almost every expression input I've added to circuits

The length of the wires shouldn't matter too much, but you could get a length of shielded cable just in case

 

[iamjackslackof]

Awesome! I'm glad it's as simple as I imagined it could be. And good call on using shielded wire, I'll probably do that just to be safe.

 

[MichaelW]

@iamjackslackof What Wah PCB board are you using? This sounds really interesting to me but I'm having a hard time imagining how it works.
How does an expression pedal physically actuate the wah pot?

I'd like to build a wah pedal but ideally it would be a "fixed wah" pedal that I could control remotely with an expression pedal. Not sure I want to go down the route of actually building one in a Wah shell.

 

[iamjackslackof]

I don't have a specific wah board picked out yet. I have some old Crybaby ones I might repurpose.

My conception of it is I will have the wah pot in a wah pedal, but with each pin of the pot going to a lug of the TRS jack. Then a TRS cable going to the remote pedal TRS jack, which will connect to the 3 pads where the pot would normally go.

 

[RetiredUnit1]

I don't have a specific wah board picked out yet. I have some old Crybaby ones I might repurpose.

My conception of it is I will have the wah pot in a wah pedal, but with each pin of the pot going to a lug of the TRS jack. Then a TRS cable going to the remote pedal TRS jack, which will connect to the 3 pads where the pot would normally go.

If you use shielded won't you need another connection on one end only for the ground? Or just ground to the pot ground or? I use shielded on the first and sometimes second stage of tube amps and grounding to the pot or jack can introduce noise into the circuit. Of course were talking much higher voltage.

If you ever do need more than 3 you can always use GX16 (16mm) connectors, GX20's have an even higher number of pins..... Super hefty avionics connectors, available at Tayda....

 

[iamjackslackof]

I hadn't considered the ground, good call. Those connectors looks pretty sweet, I may have to go with those, for looks and cool factor alone if nothing else.

 

[RetiredUnit1]

I hadn't considered the ground, good call. Those connectors looks pretty sweet, I may have to go with those, for looks and cool factor alone if nothing else.

Yeah, they are awesome looking, a big part of my choosing them for a DC power project !!!

 

[Feral Feline]

Thread reminds me I need to fix my Yamaha expr-ped.


The fixed-wah I'd like to build is the Maestro Boomer2 — Kula did a vero layout for it in the 2016 Nov 4th issue of Tone Report.
If anyone is interested but can't find that TR issue, just PM me and I'll email the PDF. I might try to build it on a re-purposed PCB instead of vero.
Maybe on the PedalPCB Station Wah, if it's close to compatible at all.

Speaking of which, for a couple months I've had a PPCB-SW built (based on Dunlop’s GCB-95), but have yet to find time to drill the enclosure (garage is freezing cold, and where the drill-press is so I'm disinclined to drill right now). Might add an expression jack but doubt it, as I've made a lot of special modifications myself. Not much room left in the enclosure as it sits.

 

[Chuck D. Bones]

If you use an external expression pedal, the pot in the exp pedal should be 100K. Most exp pedals have 10K pot which will load down the CryBaby 1st stage and degrade the performance. Wah pots are a special taper, so you'll have to experiment with A or B taper.

OR...
You can replace the wah pot with and LED-LDR opto-coupler and use the expression pedal to modulate the LED current. Connect 100K to 220K resistor (best value depends on the LDR's resistance range) from wah pot pin 2 to pin 3. Connect LDR from pin 1 to pin 2. Make sure there is a resistor in series with the LED to limit the current when the exp pedal is maxed out. Among the many advantages of doing it this way is you can have a very long cable between the exp pedal and wah pedal and you won't introduce any noise because the audio signal does not flow thru that cable.

 

[iamjackslackof]

My idea was to use an actual wah enclosure with just the proper wah pot, or put a wah pot into an expression pedal shell. I am concerned about noise that way, since the audio signal will be going over the cable. If I can't manage the noise well enough, I may try your method to modulate the LED current, thanks for the idea!