Switching between two inputs.

[H4T]

I'm trying to make a wah pedal that doubles as an expression pedal. Two inputs - one normal, one from the pedal that wants to be expressed. I can't figure out a way to switch between those two inputs and have it do what its supposed to.

I've gotten so far as to figure out this;
User hits on switch -> signal goes to new switch (switch between wah, exp.) -> if 2nd switch is in Wah mode, signal goes to FX circuit -> if 2nd switch is in exp. mode, signal goes straight to the rocker pot only.

Ahhhhg, but any time I try to draw stuff up, I come into problems - bypassing effect completely, etc. My brain is going to explode...how do I switch between two different inputs, as well as have true bypass?

[H4T]

Hm..*bump*

[Andi]

I reckon it'd be easiest with relays.

[NaBo]

There's a lot to consider here...  i'd direct you to this thread here which came up with a simple search and should answer nearly everything http://www.diystompboxes.com/sboxforum/viewtopic.php?t=28355&highlight=expression+pedal+wiring, but as you can see, it's now almost useless...  :roll:  ..... j's posts are great though, you can kinda fill in the blanks i guess.

I think what might help you is not to think of the expression pedal jack as another input... it's more an input and output.  Hence, a stereo jack (in, out, ground).  You can do some switching with the jack if you're tricksy... but i think in your case you wanna be able to have something plugged into all the jacks at the same time and be able to switch between them... right?  In that case maybe have the jack connect the wah if nothing's plugged in?  To be clear on the switching you'd like... you want to have the guitar signal going through the wah circuit or bypassing it, and, if and only if the wah is bypassed, another switch is able to switch the pot in on some other effect to work as an expression pedal... correct?

Unfortunately I gotta get up and go to work in 6 hours, but if theres no other replies tomorrow, I'll try to help you reason through this.  I'm no expert, but I love the challenge of figuring out switching schemes.  Hopefully without resorting to relays unless absolutely necessary :wink:

[H4T]

lol, all of Torchy's posts in that thread say "crp." Rather amusing, but unhelpful, lol.

I drew up a little drawing depicting how this setup will look, I hope it helps. I want the guitar signal to go through the wah circuit when the "Mode" Button is in its "on" state. When the Mode is on its other state (not wah), I want it to use the pot as an expression for the expression line.

This really seems complicated, lol. If you can figure this out in anyway at all (if you can think of a more effecient way than I drew up, let me know) I will revere you as a god for as long as you live, lol.

[NaBo]

lol, all of Torchy's posts in that thread say "crp." Rather amusing, but unhelpful, lol.

Yeah, a while ago he edited everything he posted... lost a lot of great info

Hmm... okay... Well this is somewhat difficult because the only way i can think of doing this is pretty simple, BUT, would allow for the guitar signal to be going to the wah circuit, but the pot being used for the expression circuit...  Hence no signal.  That would be when the bypass switch (your on/off one) is "on" and the mode is set to expression.  Is that acceptable?  It shouldn't be a problem unless you plan on switching from wah to expression mid song...  toggle or stomp?

Use a stereo switching jack for the expression jack, and i've shown how you can ensure the pot will always be connected to the wah circuit.

I left LED switching blank, im sure you could figure it out...  you can use bi-colour LEDs if you want.  Possibly have both LEDs turn red if they switches are set the way I warned you about...  bypass switch off, mode switch to expression (and something plugged into the expression jack i spose... cuz if nothings plugged in & you use the closed circuit jack, it'll just go through the wah...  hrmm... confused enough yet?  :wink:)

I haven't shown grounding for jacks.  BUT!  Watch the potential for a ground loop here...  The expression cord will likely be connected somewhere else in your chain, so you'll have to isolate one of the jacks so that the shield is connected at one end only.  I'd suggest isolating it on this pedal, instead of having to do it on every pedal you wanna use it with.  You can go here to figure out how to add an expression jack to any pedal over here http://www.commonsound.com/other/genmods.pdf

I'm sure this will work, but not sure if it's the BEST way...  someone else feel free to chime in.  Keep in mind the wah doesn't use the full rotation of the pot... not to mention issues with tapers.  If you want to use this with a range of pedals and get good results, take the time to read up on Andrew's (aka The Tone God) Rock n Control and Adding an Expression Pedal to Any Effect Articles.  You'll be glad you did.  With the principles discussed in these articles you can make a killer expression pedal with many adjustable elements.  It can all go between your mode switch and the jack, the small "" board in my diagram.

Okay, i think i've said a mouthful here, so without further ado, heres the diagram.  Let me know if you have any other Q's man, & good luck!

[H4T]

Shnickys! That is deep, I am very impressed lol.

From what you were saying about the potential for a ground loop and problems when mode is "expression" and bypass is "off." After this thread, I think I should have this rocker be used solely as a Wah pedal, then build my own rocker if I still want an expression pedal, so I have two clean, seperate pedals.

Great job with that though, I'm still trying to understand it all! lol

[NaBo]

The ground loop problem would only arise if you were using it in expression mode and it was connected to another pedal in your chain... here's a diagram. Happens when using a daisy chain power supply too.  There's a few ways to prevent it, but the easiest in this case is to just not connect the sleeve of the cable you use at one end... ie, isolate the expression pedal jack from the chassis in your wah/expression pedal (and don't wire the sleeve lug to ground of course).  The shield will be connected at the pedal being controlled instead.

The little switching problem arises from using the two independent switches.  If you use a toggle, don't switch in the middle of the song, or are careful to remember not to have expression mode on when the wah circuit isnt bypassed and there's a plug in the expression jack, it's not a problem at all.  That would be the main advantage that using a relay and one switch would offer (too bad they don't make 5pdt stompers ... well if they do they're probably 40 bucks).  You could have one mode in which the wah pot was being used for the expression pedal and the signal goes in and out the unit unscathed, and another in which the signal went through the wah circuit and the pot was used for that.

Or just be boring and make two...  :roll: ........    heheheh... kidding :wink: