In need of a wah circuit that can be modified to be controllable

[Timmy73]

Hey everyone. I had an idea for a pedal based on a wah circuit. However, I need a way to control the filter frequency with a different source (it will be modulated). Does anyone have any good base circuits I could start with? I imagine I could use a pre-existing wah circuit and replace the pot with a jfet or npn transistor. But, how would I know what to use? (I'd prefer not to use ldrs/vactrols) Sorry if these are noob questions, as I am not much more than that lol 

[Fancy Lime]

Have a look at Tim Escobedo's legendary circuit snippets:
http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/snippets.html

Many wah and filter circuits there that may fit your bill. The "Idiot Wah" is an excellent starting point for what you want to do. It is similar to many other transformerless wah circuits.

Andy

[Rob Strand]

It depends if the wah *has to be* a traditional wha sound or not.  That's something you need to decide upfront.

An example of an electronically controlled wah is the Boss TW-1,
https://im3.diagramasde.com/6965_roland-boss-tw1-touchwahpdf.jpg

Here the wha pot is replaced by 2xopamps and an opto.  The "pot" control is the opto LED current.
In the case of the TW1 the opto LED current is controlled from the signal envelope but you can
strip out that whole part of the circuit and  drive the LED with a manual circuit.

You might be able to remove the opamps, add a buffer or two and do a divider more like the traditional wah pot with an opto.   It would be possible to do a JFET version but it would require some design work.

[Vivek]

On another FB forum, I was associated with a project to make the SNOWWHITE AutoWah have an expression pedal and also be Midi controllable.

OTA controlled SVF can be electronically controlled easily. The OTA SVF is basically a VCF.

This VCF approach is easier and superior than attempting to replace Wah pot with a FET or BJT

http://revolutiondeux.blogspot.com/2012/07/mad-professor-snow-white-auto-wah.html

[bluebunny]

I'd look at any number of VCFs.  How you control it is then entirely at your whim: if you can produce a controlling voltage (manually, steady, modulating, or whatever), then the world is your lobster.

[Timmy73]

Have a look at Tim Escobedo's legendary circuit snippets:
http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/snippets.html

Many wah and filter circuits there that may fit your bill. The "Idiot Wah" is an excellent starting point for what you want to do. It is similar to many other transformerless wah circuits.

Andy

I know of that place. Lots of cool effects on there. I'm not sure I like the idiot wah all that much, I feel like the dissimilar capacitor values in the twin tee would make it sound weird, but I am no expert. If I were to use it, would it be better to replace the pot with a jfet or a bjt?

[mac]

SVF can be tweaked in many ways. I posted a ciruit, maybe in the LTSpice section

The inductorless Colorsound Wah is another simple circuit that sounds good. There are a few threads here too.

mac

[ElectricDruid]

+1 for VCFs.

The state variable filter (SVF) has been used for loads of wahs and autowahs. There are a ton of ways to do it, and if you want to avoid vactrols (why?) then an OTA like the LM13700 is a clear choice - that gives you a design like the Snow White posted earlier.

[Timmy73]

and if you want to avoid vactrols (why?)

I'm not sure why, I just don't like them. I feel like they are too physically sensitive and I would prefer to keep everything fully solid-state.

[Fancy Lime]

Vactrols are actually among the more robust components and definitely fully solid state. They can be a bit hard to get, though.

[Kipper4]

Look here.
Sabrotone SVF


http://www.sabrotone.com/wp-content/uploads/2012/12/EnvelopeSVF.png


Advantages. 3 possible outputs.

Ic1B pin7
Ic1C pin8
Ic1D pin14

I can't recall how I did it but I put a pot in series  or parallel with vactrol.
It will give you more control of the SVF bandwidth.

I'm pretty sure I used a different envelope dectector.
Either way I'm sure if you mess with this as a base and adjust to taste you'll come up with a usable circuit.

Have fun
If at first I don't succeed , I learned what doesn't work and rule it out.
Try something else at the other end of the scale and work towards the most dale path.
Zen.......

[PRR]

Welcome!

....I feel like the dissimilar capacitor values in the twin tee would make it sound weird....

How could you even know? Unless you put your head in the middle of the Tee. Which would be weird.

[ElectricDruid]

Vactrols are actually among the more robust components and definitely fully solid state. They can be a bit hard to get, though.

+1 agree about robust, and not that hard to get. There are plenty of sources for the Xvive clones, and while they might not be "exact" clones (if that were even possible?), they do the same job. Maybe tweak a resistor here or there, but that's always the case with vactrols - unless you accept a certain variability, as many of the original pedal manufacturers clearly had to!

No-one has complained much about the FilterFX, which is based on these modern components. The design limits the effect of vactrol variability, and that solves most of the issues.

[Rob Strand]

How could you even know? Unless you put your head in the middle of the Tee. Which would be weird.

In fact for inductorless wah circuits like the colorsound wha and idiot wah you cannot get the Q's high enough with equal cap values to sound like a real wah.

https://www.diystompboxes.com/smfforum/index.php?topic=121430.0
(Some maths for the idea is here,
https://www.diystompboxes.com/smfforum/index.php?topic=127045.msg1217044#msg1217044 )


Worth checking out transmogrifox's design is reply #38 in the first thread.