Rack-mounted wah with controller pedal

[gdgross]

Over the last couple of years, I have made the transition from a traditional amp/pedalboard setup to a rack setup with a midi floor controller. Versatility was the driver for this. The "brain" of the system is a tc electronic G-system, which basically acts as my rig master controller, with some good time-based digital effects.

I have moved all of my OD boxes to the back of my rack, which keeps my floor controller setup nice and clean. One cable from floor to rack. That's it. Super easy and fast setup.

The fly in the ointment is my wah. I used to use a heavily modified and beloved VOX 847 wah. Great pedal. The rub is that if I want to use that wah, I have to run two extra cables from my rack, which I don't really want to do. (Currently I'm using the built-in g-sys wah, which sounds fine, but the feel is definitely not right.)

I have learned that dunlop makes a rack-based wah system. http://store.jimdunlop.com/product_i...products_id=28 basically your tone-generating elements and all audio are in the rack, and you control that with a controller pedal connected via a stereo cable. The downside is that this is super-expensive. $600.

I'm thinking maybe I could to the same thing with my vox: take the guts out of the pedal, stick in in a box, and use the pedal to somehow control the pot in the box. The advantage is saving myself a cord, and keeping all the audio in the rack, which I really like.

Anyone have ideas as to how this could be done? Digitally controlled pots? A pot in the footcontroller driving a voltage divider driving some kind of analog pot emulator?

Any ideas how dunlop does it? Are there such things as voltage controlled pots? I know there are digitally controlled pots, but I'd really rather not get that sophisticated if I can avoid it.

Thanks!

[R.G.]

I've built a few of these for rack-oriented friends. It's pretty easy.

You obtain an LED/LDR variable resistor module. You take the whole circuit board for your wah and mount it in your rack cabinet, and put the LED/LDR in there instead of the wah pot. The rocker assembly keeps the original wah pot and uses it to control the current through the LED back in the rack.

It works well - I got good reviews from friends on the ones I built.

The circuit for how to do it is on my web page here:

The Technology of Wah Pedals. Scroll down until you see "Anderton".

[gdgross]

Thanks RG! that's exactly what I'm looking for.

Any suggestions on LDRs/LEDs? I have no experience with LDRs, and LEDs only as panel indicators. Do I just buy a couple and heat shrink them together a la Fender?

[R.G.]

You can roll your own. But if you can find an NSL-32 from Silonix (?) or a VT5C3 module for about $5, the hard part's done. These have matched source/LDRs and may save you some experimentation. On the other hand, LEDs and LDRs are cheap when you get them surplus, so you can go that way too. I used the NSL-32.

[gdgross]

Thanks! just ordered a few of the NSL parts from small bear.

This may turn out to be easier than I thought.

[gdgross]

Well, it did turn out to be easier than I thought. But the sweep of the pedal is all wrong. I tried it a couple of ways.

First, following the schematic on your site, RG, with the 100k resistor on top of the LDR. It works, but the pedal sweep moves very quickly from bass-y to treble-y in only a small amount of physical movement.

Next I tried adding another LED/LDR combo "on top" of the one already in there (replacing the 100k resistor). I wired up the LED and limiting resistor backwards from the other one, so that as one LED get brighter, the other would get less bright. And, correspondingly, I theorized that the LDRs, when stacked to make a three terminal "potentiometer", would behave a little more like the pot I was trying to replace. The sweep in this case was only marginally better, if at all; it was mostly the same. It still went from very bassy to very trebly with very little pedal motion.

Perhaps these LED/LDR combos (I used the NSL-32 as you suggested) are not very linear and don't track the pot movement linearly?

Any thoughts? Should I try a different part? Make my own LED/LDR with some heat shrink?

It's kind of a pain to work on this thing, as it's housed in a 1u chassis with three other pedals in the same box - all wired up with cable and power in the guts of my rack...so I'd like to entertain some though experiments before I tear everything apart three times a week to do some tests...

[52 Bill]

Other than the sweep of the pedal, is the sound of the wah satisfactory?

If it is, I think that what you would want to try to adjust is the voltage that is getting to the led in the NSL-32, and not the resistances in the audio path.

I think that what's happening is that the led turns on and off too fast for your liking. If you limit the range of voltage applied to the led (or actually change the way the voltage is applied to the led), you can alter the "sweep" of the wah response.

[gdgross]

Other than the sweep of the pedal, is the sound of the wah satisfactory?

Yes, I think so. It's just a little hard to tell, because for me the feel of the pedal affects the way I play a lot. That was the whole reason for trying this crazy idea instead of just using the wah in the g-system anyway. The g-sys wah sounds great, but I haven't been able to get a feel I like from it with any pedal I've tried.

I will try messing around with limiting the voltages driving the LED. Particularly the "on" voltage, I think is being applied too quickly. Assuming the "on" state corresponds to the trebbly side of the wah function.

Another thing I thought of last night: I did add a 500Ohm resistor and green indicator LED in the pedal itself, mainly for another cool little light. It's in parallel with the extreme ends of the pot. I don't see how this could possibly affect the function of the pot/LED however.

[52 Bill]

Another thing I thought of last night: I did add a 500Ohm resistor and green indicator LED in the pedal itself, mainly for another cool little light. It's in parallel with the extreme ends of the pot. I don't see how this could possibly affect the function of the pot/LED however.

Did you build this circuit from R.G.'s site, based on Craig Anderton's original design? I haven't seen the circuit for awhile, but I thought that Anderton had some parts added to slow the response of the pedal down, like a cap and resisitor on the wiper or something? Maybe the second LED is drawing too much current and changing the response. I'll go check out the schematic again.

[gdgross]

Did you build this circuit from R.G.'s site, based on Craig Anderton's original design? I haven't seen the circuit for awhile, but I thought that Anderton had some parts added to slow the response of the pedal down, like a cap and resisitor on the wiper or something? Maybe the second LED is drawing too much current and changing the response. I'll go check out the schematic again.

Yes, I used that exact circuit - with the exception of a 0.36uF cap instead of 0.22 since it was what I had on hand.

There is a cap and resistor (I assume current limiting resistor to take care of the top of the wah pot sweep) but I don't think that would affect the sweep too much. It's not the speed of the sweep that feels wrong, it's that there is too much sound change for too little pedal movement.

[52 Bill]

Then really what you don't like is the taper of the actual pot in the pedal. I looked up the schematic, and the 2K2 resistor is there to limit the current to the LED and the 0.22 uf cap is there to stabilize the changing voltage at the wiper of the pot.

Check R.G.'s site for his pot tapering page. I know he offers some suggestions about how to adjust a pots' taper by adding resistors across the different terminals. Maybe this will work for you.

[gdgross]

Then really what you don't like is the taper of the actual pot in the pedal. I looked up the schematic, and the 2K2 resistor is there to limit the current to the LED and the 0.22 uf cap is there to stabilize the changing voltage at the wiper of the pot.

Check R.G.'s site for his pot tapering page. I know he offers some suggestions about how to adjust a pots' taper by adding resistors across the different terminals. Maybe this will work for you.

Hm.

I didn't mind the taper of the pot at all when it was in the wah circuit without the remote control business...

I'm going to try some things out this weekend, including messing with the pot taper via resistors.

[52 Bill]

The pot was controlling the audio signal when it was in the wah circuit. As part of the voltage divider circuit, it is not controlling the same thing. The response can't possibly be the same.

[4nkam]

Cool thread. Anything new? If you're interested, I have some pix of the dunlop 1sr and 2sr guts.

[gdgross]

Cool thread. Anything new? If you're interested, I have some pix of the dunlop 1sr and 2sr guts.

No, I still haven't got the sweep working right, but I haven't had time to mess with it in a month or so. I've been using my g-system wah in the interim.

I'd love to see the pics if you don't mind. My email is:
gdgross
AT
gmail
DOT
com

Thanks!
Geoff