Remote Wah Control / jfet VCR or LDR?

[Rich G.]

I remember reading an article somewhere (here, I thinks??) about replacing a WAH pot with an LDR then controlling an LED voltage remotely, but I can't find it!

So, here's what I'd like to do:
1. Remove the guts of my 535Q Wah and put them into a smaller chassis then mount in rack.
2. Replace the WAH control pot with some sort of controlled resistor... Either a LDR or perhaps a jfet configured as a voltage controlled resistor will work??  not sure.

Any thoughts on remotely controlling a WAH pedal??

[Hal]

LED - LDR is kinda hard to do...you need something that would gradually dim the LED...like some kind of plastic that goes from light to dark...unless you're talking about using the pot already in the wah....


That might work...it would be used to control the current through the LED, not the voltage of the LED, though.  also, i dont really see the point....

what is the idea, to get a more controllable sweep range, more gradual....something else ?

[maximee]

Hal:
I guess he is just trying to get his pedalboard down to a more comfortable size

[Hal]

OOOH I (kinda) see!

When you said "2. Replace the WAH control pot with some sort of controlled resistor... Either a LDR or perhaps a jfet configured as a voltage controlled resistor will work?? not sure. " I thought you meant in the wah chassis...

More important than deciding what type of resistor you're gunna you, use need to figure out what type of chassis you're going to use/make.  

Do you want it as a "set and forget" style parametric boost ?

I still dont quite understand the aims here.

[R.G.]

Craig Anderton did a remote wah pedal article in his GP effects series. The article was called "Clean up your wah pedal" or something similar.  I've built it, and it works just fine.

The idea is that you use an LED/LDR optocoupler to replace the wah pot in the effect circuit, and then use the physical rocker pedal and pot out at the end of a long cable to vary the current to the LED. That varies the LDR resistance and makes for wah.

You can use a single stereo 1/4" jack to run power and ground to the rocker pedal and return the wiper signal back to the LED.

[KarbonHed]

How do they do it in the rackmount crybabys people like Ty Tabor and Slash use?

[smoguzbenjamin]

Probably something like RG said.

[The Tone God]

Rock N' Control

This may give you some ideas.

Andrew

[John Catto]

Here's the Anderton article. Look at the date! I can't believe I've kept this that long (or did it when it came out )

[zachary vex]

i'd recommend an LDR over a fet.   i've listened to both side-by-side and the fet circuit has some nasty distortion.

[R.G.]

i'd recommend an LDR over a fet. i've listened to both side-by-side and the fet circuit has some nasty distortion.

Like most electronic devices, the JFET connected as a VCR has a limited signal handling capability. It's OK for low output guitars, starts to distort in the simple VCR connection with mid to high output pickup signals, and any amount of overdrive or boost ahead of it will make for distortion.

Whenever a VCR connected JFET has a signal voltage of a significant fraction of the Vgs bias, the signal voltage modulates the channel voltage, causing an equivalent change in the effective Vgs bias voltage. You can get rid of a lot of that for signals up to about a volt or so by feeding back about half the drain signal to the gate. This helps cancel the channel modulation. Phase 90's, as an example, get much cleaner sounding if this is done to them.

The LDR has a much lower intrinsic distortion, of course.

[brett]

For those more capable with electronics than mechanical devices, you can also use a Hall-effect sensor to control the brightness of an LED, illuminating an LDR and doing the wah thing.  

So what the hell is a Hall effect and its sensor?  Well, it detects a magnetic field.  In the case of a wah, you can put a magnet under the pedal, and have the sensor, etc in the base.  I've done it and it works well.

[Hal]

i still dont think i understand the goals here....if you do the LED-LDR thing with a pot, you still need to have a pot in the pedal.  Why not just use the pot directly ?  I guess its for the sound but...

in other words...how does this mod effect the sound?

[william]

It doesn't apply to this conversation, but to answer Ha'ls question, a LED/LDR doesn't get scratchy.  It will also cover some of the effects of a scratchy pot.  Mostly the hideous scratching sound.  I did it to my old crybaby bass wah and it helped alot.

[John Catto]

i still dont think i understand the goals here....if you do the LED-LDR thing with a pot, you still need to have a pot in the pedal.  Why not just use the pot directly ?  I guess its for the sound but...

in other words...how does this mod effect the sound?

Point one is that the pot will no longer introduce "scratch & pop" noise into the signal chain. The Anderton article explains this at some length.

Point Two is that once you have voltage control of the "pedal" you can run any desired length of cable out to a remote pedal ie. the rack mount + remote pedal idea discussed earlier.

[Rich G.]

i still dont think i understand the goals here....if you do the LED-LDR thing with a pot, you still need to have a pot in the pedal.  Why not just use the pot directly ?  I guess its for the sound but...

in other words...how does this mod effect the sound?

Point one is that the pot will no longer introduce "scratch & pop" noise into the signal chain. The Anderton article explains this at some length.

Point Two is that once you have voltage control of the "pedal" you can run any desired length of cable out to a remote pedal ie. the rack mount + remote pedal idea discussed earlier.

Sorry-- gigs this weekend kept me pretty busy.  Thanks for the reply guys!

Yes, the main point I was originally after was this:  I want to put the Wah circuitry in my rack so I don't have to run a long audio line out and back to the pedal board.  The wah will then reside in a loop of my GCX switcher connected via short audio lines.  I'll then run a CV signal from the pedal board back to the rack... perhaps even use a MIDI to CV converter so I can control the wah via MIDI CC.

[Hal]

cool :-D

[nero1985]

the article u r looking for is at GEOFEX.com, its a really simple mod that im trying to build, now i have the schematics to do that on Dunlop GCB-95, email if somebody wants it nero_hans@hotmail.com,,, NOW, i have a question about it, if anybody has done it what type of LDR (photocell) did u use? they have them at www.smallbearelec.com but there are several types so im not sure of wich is the right one for that