Switching Q - I'd like to make a wah pedal that's also an active volume pedal

[midwayfair]

I rarely use wah, and only in a couple songs, but I do use a volume pedal a LOT. I really only have room for one on my board, and it seems to me that the most efficient way to get some wah into my pedal board's life is to make it a volume pedal in bypass.

Using RG's vox-alike schematic here ...



I'm planning on using buffers at both the input and output of the effect. What I'm trying to figure out is the minimum number of components I need to switch out to use the same pot for both.

-Can I get away with just switching the wiper and lug 3 to the "Output buffer" (wiper -- where the 220nF + lug 3 are connected in the wah circuit) and input buffer connection (where lug 3 goes when switched), or will I get some interference from that 220nF cap?

-Should I do it instead where I disconnect the entire wah output and move the two lugs of the pots?

-Or should I resign myself to using a 4PDT if I want this to happen? (switching the wah output and both lugs of the pots and one row for the LED).

-Is there some sort of active switching system that might be better suited for this? Maybe I could use a couple H11F1s to control what the wah pot's lugs do? (Then I'd only need enough switch poles to light the appropriate LEDs and perhaps switch out one other component, like the 220nF.)

Is there a different inductor-based wah I should perhaps look at that would allow an easier switching system?

[armdnrdy]

You do realize that a wha pedal's pot is adjusted to where it never reaches zero resistance?
This means that you would never reach zero volume.

Unless someone has come up with a work around circuit for this issue, I would look toward fabricating a bracket to hold an additional pot actuated by the same pinion gear for the active volume circuit.

[midwayfair]

You do realize that a wha pedal's pot is adjusted to where it never reaches zero resistance?

No, I didn't realize that. [EDIT: What IS the typical minimum resistance? I don't necessarily need a kill if we're talking about only a few hundred ohms.]

Hrm, maybe I should look into using Anderton's LDR method. I could use the same pot and just switch which LED is on (which could also handle the LED indicator. The minimum resistance won't matter at all in that situation and I can use the other poles of the switch to switch the output between the wah and VP effects.

[armdnrdy]

I was thinking about something along those same lines. I did a bit research on making a universal expression pedal circuit for effects. It involved producing different control voltages with the same 10K expression pedal pot.

If the Anderton circuit doesn't pan out.....there's this:



The 95Q I have in front of me measures 30K lowest resistance.

[R.G.]

I rarely use wah, and only in a couple songs, but I do use a volume pedal a LOT. I really only have room for one on my board, and it seems to me that the most efficient way to get some wah into my pedal board's life is to make it a volume pedal in bypass.

First, look at all the options. I'll list a few for you to consider after I talk about your questions.

I'm planning on using buffers at both the input and output of the effect. What I'm trying to figure out is the minimum number of components I need to switch out to use the same pot for both.

Meta-observation: Kudos for figuring out some metric, some objective of how to get to what you're trying to do.
Comment on the actual objective: trying to figure out the minimum number of parts is often not the optimum way to do things when considered from the outside - use by the player and cost to build. Let's take cost first. The cost of electronic parts is zero, to a first order, compared to the cost of enclosures, jacks, pots, knobs, and so on. If you can do whatever you want by a small board of electronic parts and minimize the disruption to the user-interface parts, you often come out ahead. At least that's a metric I often use.

-Can I get away with

You can get away with opening the capacitor that connects the inductor to ground. This is what at least one historical volume-wah pedal did. The bad part about that is that the rotation of the pot for volume use is backwards; heel down is max volume. And there's that "won't go all the way to zero" thing, too.

just switching the wiper and lug 3 to the "Output buffer" (wiper -- where the 220nF + lug 3 are connected in the wah circuit) and input buffer connection (where lug 3 goes when switched), or will I get some interference from that 220nF cap?

-Should I do it instead where I disconnect the entire wah output and move the two lugs of the pots?

-Or should I resign myself to using a 4PDT if I want this to happen? (switching the wah output and both lugs of the pots and one row for the LED).

-Is there some sort of active switching system that might be better suited for this? Maybe I could use a couple H11F1s to control what the wah pot's lugs do? (Then I'd only need enough switch poles to light the appropriate LEDs and perhaps switch out one other component, like the 220nF.)

Is there a different inductor-based wah I should perhaps look at that would allow an easier switching system?

Since you're asking what you should do, I'll post some of my opinions. The physical setup of the typical "Crybaby" style wah is at least acceptable to many people. It has some issues when used for a volume pedal, mostly with not using the full travel of the pot. Some expression pedals are better strictly as far as pot travel is concerned.

If I were making this, I would put in two buffers, one for input to a volume pot, one after. This frees you from treble loss/loading issues from the pot. I would pick a pedal enclosure based on availability and personal preference - how it works with my own personal overgrown feet.    I'd probably use a dual section pot; one for the wah, one for the volume, to give me freedom on the rotation direction issue. Then I'd make the selector switch pick either the internally independent wah or volume circuits by selecting an input and an output.

You can resolve the pot direction issue by switching all the hot and cold sides of the pot with either a mechanical switch, or a relay, or electronic switching. The CD4053 is nice for applications like this, and in fact could switch all three pot terminals between two circuits in a single chip.

I guess my advice is that it may be simpler to make work well and easily to build two different circuits (a wah and a volume pedal circuit) into the same enclosure and then select between them in some kind of A/B circuit than to modify the wah circuit on the fly with switches. Switching between two circuits is well known and predictable. Switching the internals of the wah circuit is not so much.

[midwayfair]

RG, thanks for your help. In particular, it didn't occur to me that dual gang pots might exist for something like this, though of course it makes sense since stereo volume pedals exist. Unfortunately, I'm not sure I can find one for the Vox shell. And the "doesn't get all the way to 0 resistance" part really is a major issue here.

One clarification: When I said "minimum number of components", I only meant as far as killing the wah circuit; I'm not really concerned about the costs or space in this case, but rather the physical limitations of mechanical switches. If I needed to switch out more than 4 components, then I'm SOL as far as stomp switches are concerned (4PDT) and absolutely must go with electronic switching.

In any case, I'll have to go with the expression pedal pot, which means I could eiher go with an LDR-based solution (the VTL5C1 should work really well for the volume pedal half, and the cheap LDRs from Tayda should be basically perfect for the wah half) and then I can use normal bypass switching, or just find an appropriate dual gang.

[R.G.]

One clarification: When I said "minimum number of components", I only meant as far as killing the wah circuit; I'm not really concerned about the costs or space in this case, but rather the physical limitations of mechanical switches. If I needed to switch out more than 4 components, then I'm SOL as far as stomp switches are concerned (4PDT) and absolutely must go with electronic switching.

OK. The limit is a 4PDT, and you don't mind spending on electronics parts.

If you go the route of putting two entire effects in there, you only need a DPDT to switch between the inputs and outputs. If you need an indicator LED, you can use a 3PDT to change an LED, perhaps changing the color of a bicolor LED and letting the main bypass switch outside of the effect circuit selector turn the LED on and off.

[Gus]

third post
http://www.diystompboxes.com/smfforum/index.php?topic=103521.0

[midwayfair]

I just realized this is TWO different pots in the same gear. That's ridiculously clever and would solve almost every problem that's cropping up here. Did you happen to do a build report for that? How did you mount the second pot in there?

[armdnrdy]

I just realized this is TWO different pots in the same gear. That's ridiculously clever and would solve almost every problem that's cropping up here. Did you happen to do a build report for that? How did you mount the second pot in there?

This was not my project. I pulled this picture for future reference from the net. (possibly this sight) (credit goes to OP of image)

The image is pretty self explanatory, a piece of aluminum folded at a 90 degree angle, (home depot sells aluminum angle stock that would work) a notch cut to fit the second pot, (volume) two holes drilled in the bracket, two holes drilled in the enclosure, nuts and bolts to secure the bracket, source a pot with the same diameter D shaft as the wah pot, cut the wah pot shaft down about half length, slide the pinion gear back on the original wah pot, now you have room in the pinion gear for the volume pot shaft.

I think that this arrangement with a separate volume pedal circuit, switching between the wah and volume would be the way to go.
You could even use a "kick switch" (alternate action switch) (see crybaby 535Q) on the side to switch between the two.

I might just do this myself!