Alternative Wah controllers?

[psychedelicfish]

Hi there!
I was thinking recently about how to make a wah pedal from scratch (enclosure and all) and was trying to work out different ways to control the sweep. So far I came up with:
Pot
A foot controlled potentiometer, the standard for most wah pedals

Variable Capacitor
Not sure how to implement this from a circuitry point of view, though RG mentioned RF oscillators in a recent thread (lost to forum crash). This could easily be done with two moving plates.

Variable Inductor
Again, not sure about this on the circuitry front, but it could be done by moving a steel/iron core in and out of the middle of a coil.

Optical
Can be done either by moving a light proof medium in and out of the gap between a light source and an LDR, or by mounting an LDR on the outside of an enclosure and using feet etc. to limit the amount of light getting to it.

LFO
Fairly self explanatory.

Envelope
The amplitude of your signal over time

Those are all I can think of as of now. Are there any others you can think of? Any ideas about how to implement them? Pros and cons? Examples of circuits using some of these?
Thanks,
Edward

[Seljer]

The DOD FX17 uses a variable capacitance to control an high frequency oscillator. It then has a frequency to voltage conversion circuit and the actual filter is a OTA based voltage controlled filter.
http://www.diyguitarist.com/DIYStompboxes/FX-17.htm

Another variation on this scheme would be the Zvex Wah Probe



Or embrace all this digital stuff and stick an accelerometer chip in there (that Source Audio Hot Hand thing....and the new EHX wah wah?)

[samhay]

If you were happy to only sweep in one direction (at a time), you could use a momentary switch and an integrator to generate a DC sweep that would then work in a similar way to an auto-wah. This is one of the options in my never-ending sort-o-wah and it works pretty well if e.g. you only want to sweep from heal-down to heal-up.

[psychedelicfish]

So I now have an idea of how to do a variable inductor wah, the kay wah. Here is a schematic:

[samhay]

So I now have an idea of how to do a variable inductor wah, the kay wah. Here is a schematic:

You might want to convert that to run from +9V so you have a reasonable amount of headroom.
Have you seen an appropriate inductor - I think most people use audio transformers these days if they want largish inductors. I guess you could try to remove the core from one...

[psychedelicfish]

you know those torches which you shake to charge? they have a reasonably large coil in them which might work...

[samhay]

you know those torches which you shake to charge? they have a reasonably large coil in them which might work...

If you go down that route, you might want to try and modify the circuit so you can use a smaller inductor - 3H is a lot of turns. That said, you're a Kiwi right, so perhaps an iron nail and some number 8 fencing wire might do the trick?

[psychedelicfish]

I'll give it a shot... she'll be right, mate

[psychedelicfish]

jokes aside, using an iron nail is actually a good idea, because I was considering making the treadle from wood...

[WaveshapeIllusions]

You could use a gyrator in place of the inductor. Any method for achieving a variable resistance can be used to vary the inductor's value. Also, PWM is another method. Using CMOS switches variable pulse width can be used to simulate resistance. Switching between capacitors can effectively simulate a variable capacitor. There sre some filter ICs that use that method. You could probably switch between inductors too if you so desired.

[samhay]

jokes aside, using an iron nail is actually a good idea, because I was considering making the treadle from wood...

Yeah - according to wikipedia, a moveable ferrite magnetic core is possibly the way to go.
http://en.wikipedia.org/wiki/Inductor#Ferrite-core_inductor

I'm an expat and have fond memories of impaling myself with number 8 wire when I was a kid. You might have more luck trying pickup wire, but I had some difficulty finding any locally when I was last in NZ.

[drolo]

I have been using a magnet and a Hall effect detector in my Wah's Volumes and expression pedals.
The Hall effect detector has a stationary voltage of 2.5V and varies up to almost 5 or down to almost zero depending on the polarity. Hook up a led driver system after that and LDR's. you can do inverting led drivers to simulate a pot as voltage divider

[samhay]

I have been using a magnet and a Hall effect detector in my Wah's Volumes and expression pedals.
The Hall effect detector has a stationary voltage of 2.5V and varies up to almost 5 or down to almost zero depending on the polarity. Hook up a led driver system after that and LDR's. you can do inverting led drivers to simulate a pot as voltage divider

Very cool. Do you need to use a fairly strong magnet to get enough swing out of it?

[drolo]

Very cool. Do you need to use a fairly strong magnet to get enough swing out of it?

Yes i needed to use a neodym magnet. Ceramic magnets or other weaker types did not work.

(but i dont wear boots with metal tips nor do I hide my Credit cards in my soles, so it's not a big issue ;-) )

It works pretty neat once you find the right distance and tweak the led driver for best on/off results.

It's a lot easier to implement, mecanically than led/ldr arrangements with a shutter or to come up with a pot turning mechanism.

[psychedelicfish]

Now that's something I hadn't thought about. If your treadle was made of sheet metal it would provide magnetic shielding

[drolo]

Now that's something I hadn't thought about. If your treadle was made of sheet metal it would provide magnetic shielding

thats right, in a crybaby shell I have it in, the field definitely gets through but on an old Colorsound wah i retrofitted recently it was ok IIRC

[artifus]

breath control? http://rubidium.dyndns.org/cag/pdf/emm_miniblo.pdf - vca here but easy mod to vcf... or maybe a small footpump?  

http://rubidium.dyndns.org/cag/pdf/synblo.pdf

[drolo]

ooor ...

http://www.youtube.com/watch?v=PSsl1h8RhqU

[gmoon]

RE: a variable inductor wah...there's some groundwork:

http://www.diystompboxes.com/smfforum/index.php?topic=75474.0

In a nutshell--the small the inductance, the more the DC resistance of the inductor attenuates high frequencies in a typical circuit. You can bet that's why the original Kay inductor topped out at 3H. There are probably ways to get around it for someone more knowledgeable... But it's pretty obvious in simulations, too.

I used an inductor with a range of about 700mH to 100mH, and a DC resistance of about 170 ohm (half that would make a huge difference). Someday I'll return to the project...if I ever get time. I'd like to custom-wind an inductor similar to the Kay.

This is the last test, with a really clean amp (it actually doesn't sound bad with compression / a higher gain amp):
http://www.youtube.com/watch?v=KZEcr5WWQWc&;

[samhay]

RE: a variable inductor wah...there's some groundwork:

http://www.diystompboxes.com/smfforum/index.php?topic=75474.0

In a nutshell--the small the inductance, the more the DC resistance of the inductor attenuates high frequencies in a typical circuit. You can bet that's why the original Kay inductor topped out at 3H. There are probably ways to get around it for someone more knowledgeable... But it's pretty obvious in simulations, too.

I used an inductor with a range of about 700mH to 100mH, and a DC resistance of about 170 ohm (half that would make a huge difference). Someday I'll return to the project...if I ever get time. I'd like to custom-wind an inductor similar to the Kay.

This is the last test, with a really clean amp (it actually doesn't sound bad with compression / a higher gain amp):
http://www.youtube.com/watch?v=KZEcr5WWQWc&

Hadn't seen that thread before - very cool. I take it you're our resident MacGyver?