Volume-Expression-Pedal-Hybrid

[fixxe]

How would one go about building such a thing? I'd like to have one output for each and a bypass. Controlled by a 3-way toggle switch (Volume/Expression/Bypass).
Would that switch be a "on/on/on"? And how would I have to connect it?
Thanks in advance!

[fixxe]

or would I use a "on/off/on"?
I just realized that an expression pedal doesn't depend on any input signal
So how would I turn that output off?

[jkokura]

There are some pedals that could, in theory, work to do both jobs. However, I think that on average, a smarter solution is to simply get a pedal board big enough to run both a volume and expression pedal.

However, If I 'had' to do it, because of no other option...

I'd use a wah shell, and use the 'switch' to allow me to flip between 'expression' and 'volume modes. What I would do would be to hook up a bypass board of some sort to that switch, whether it's 3PDT or 4PDT or whatever it needs to be, to flip the three lugs of the pot between a set of in and out jacks, allowing it to be used as a volume pedal, and another, third jack setup for my expression control. Obviously, the wiring would have to be sussed out, and likewise, you'd have to run a direct line between the in and out control when you've flipped over to the expression mode. I'd also expect you'd need to include a resistor in line with that expression mode between the in and out jacks to compensate for any volume jumps you might get.

This wouldn't be true bypass in the truest sense, but it's a solution.

But then again, I don't think it's an idea that's properly feasible. It's better to just run a volume and an expression pedal. At least, in practice based on my experience.

Jacob

[kothoma]

The expression pedal does depend on a (DC) input signal, it's just on the same TRS plug.
And don't forget that there are two different ways of wiring TRS of an expression pedal (Roland vs. Yamaha).

I only run it through in mind but I don't think you can get Volume/Bypass/Expression with a single toggle switch.

[gtr2]

There is no standard for TRS wiring/resistance of expression pedals/jacks.  That's the bigger problem.

For instance Line 6 products just look for a varying 10k resistance between tip and sleeve.  Where a T.C. product is looking for a 250k resistance.  Eventide is 25k Strymon's not as particular on the resistance but sends between the ring and tip sending the control voltage to ground.

They are all a bit different so you need to adapt the expression to what you need to control.

Josh

[fixxe]

thanks for the responses so far! 
I guess it's not possible to do it with just one switch, not that I'd be a master at switch-wiring anyway
Could it be done with more switches? Like one switch for cutting the expression-out-signal and one switch to go between volume and bypass?

[kothoma]

1) Are you sure you can use the same pot for expression and volume?
Expresson pedals typically have a linear taper pot, volume pedals have audio taper pot.
Many expression pedals use 10k, many volume pedals use >200k.

2) What are your switching scenarios? I'm a bit confused about how you imagine this.
For example, does setting the pedal in expression mode imply bypass?
Do you need to switch by foot or is also a rotary switch an option?

3) Can volume and expression share ground or do you need to isolate one from the other?

4) More questions to come...

[fixxe]

1) Are you sure you can use the same pot for expression and volume?
Expresson pedals typically have a linear taper pot, volume pedals have audio taper pot.
Many expression pedals use 10k, many volume pedals use >200k.

2) What are your switching scenarios? I'm a bit confused about how you imagine this.
For example, does setting the pedal in expression mode imply bypass?
Do you need to switch by foot or is also a rotary switch an option?

3) Can volume and expression share ground or do you need to isolate one from the other?

4) More questions to come...

1)You are probably right. I want to use it for a Strymon Lex. So it's probably already impossible to do. How do the pedals work, that are wah and volume pedal in one though? Doesn't a wah use a linear pot too?
2)I'd like it to be either A)Bypass   B)expression + bypass    C)volume
I don't need it to switch per foot. Any switch is welcome.
3)    What would be the difference?
4)Me too

[kothoma]

1)You are probably right. I want to use it for a Strymon Lex. So it's probably already impossible to do. How do the pedals work, that are wah and volume pedal in one though? Doesn't a wah use a linear pot too?
2)I'd like it to be either A)Bypass   B)expression + bypass    C)volume
I don't need it to switch per foot. Any switch is welcome.
3)    What would be the difference?
4)Me too

1) Not sure about wahs. But it depends on the design. Could for example be an expression pedal internally controlling alternatively volume or wah.
2) OK, I'll see if I come up with something.
3) One more pole to switch... But could be necessary to avoid ground loops, depending on the setup.

[fixxe]

There's also a strymon video where they mod a crybaby as an expression pedal. so 100k seems to be fine.
they also wrote in the comments: "For the most part the pot value doesn't really matter in this circuit until you start getting to around 10k at which point you start to lose some sweep range. 25k or even 50k pots will work very well."

[kothoma]

Let's assume this works with an A250K pot (as suggested here: http://www.strymon.net/2011/10/10/strymon-tech-corner-3-volume-pedal-as-an-expression-pedal/).

You have:

the POT (I'll use these numbers for the lugs: http://www.beavisaudio.com/techpages/Pots/images/Potentiometers-front-back.png)
IN for volume
OUT for volume
TRS for expression (lets say ring is the input and tip is the output, that's Roland style)
SWITCH with 3 positions (Exp, Byp, Vol) and 3 poles (selecting POT lug 3, POT lug 2 and OUT tip)

Make these connections:

Ground: IN sleeve, POT lug 1, OUT sleeve and TRS sleeve connected together

IN tip goes to 1) position Vol of SWITCH pole 1 (selecting POT lug 3)
            and 2) positions Exp and Byp of pole 3 (selecting OUT tip)

TRS ring goes to position Exp of SWITCH pole 1 (selecting POT lug 3)

TRS tip goes (via an optional 1k resistor) to position Exp of SWITCH pole 2 (selecting POT lug 3)

connect position Vol of SWITCH pole 2 with positon Vol of SWITCH pole 3

That's it. This happens in these three positions:

Exp: IN tip goes via SWITCH pole 3 directly to OUT tip (bypassing the POT)
        and TRS ring goes via SWITCH pole 1 to POT lug 3 and POT lug 2 goes via SWITCH pole 2 to TRS tip.

Byp: IN tip goes via SWITCH pole 3 directly to OUT tip.
        No output at TRS tip.

Vol: IN tip goes via SWITCH pole 1 to POT lug 3 and POT lug 2 goes via SWITCH pole 2 to SWITCH pole 3 and then to OUT tip
        No output at TRS tip.

Sorry, can't provide a drawing. Hope this helps.

[fixxe]

thanks, i'll try that!
btw, what kind of switch do i need?

[kothoma]

Either a 4 position 3 pole (3P4T) rotary (limited to 3 positions)
or a 3 positoin 4 pole (4P3T) rotary (using only 3 poles).
Something like these: http://www.musikding.de/Rotary-Switches

[fixxe]

I finally got around to draw this out (in a really shitty drawing ), and I must say: bravo to you, sir!
Now those switches: Are those shafts really as long as they appear to be? They just seem really long, haha.

[RobA]

I finally got around to draw this out (in a really shitty drawing ), and I must say: bravo to you, sir!
Now those switches: Are those shafts really as long as they appear to be? They just seem really long, haha.

Yep, you've gotta cut 'em off (or saw, snap, melt, ...). Pain in the but really. They are plastic though.