"Character filters" / CV controlled wah

[WhenBoredomPeaks]

I wanna try a few different filter types/flavours, so far i've made an MS20, a Minimoog VCF, a Meat Sphere. A Polivoks, a Syntachon/Steiner-Parker and an Oakley Diode Superladder is in the parts sourcing stage. Are there any other "must-have" or characteristic filters? I'd rather try a modern sound/new design, i think the Moog VCF will be enough for my vintage needs.

During my search i noticed that i have not seen a single cv controlled filter design which utilized an inductor like a wah. I'd like to try my luck at modifying an existing wah circuit into a voltage-controlled one. Can i just pop in a vactrol like a vtl5cX and some resistors around it to tailor it for my needs or the reason for no one using it this way is because it is impossible? (i don't care that it is band-pass only, i have enough low pass filters already)

[R.G.]

"Technology of Wah Pedals", geofex.com, 1999. See the section on the Anderton wah retrofit and the two additional schemes for voltage controllability. And the Anderton retrofit, from even earlier, published long ago in his column in Guitar Player.

Anything that varies the attenuation of the signal fed back to Q2 changes the frequency of the Vox/inductor wah circuit.

[WhenBoredomPeaks]

"Technology of Wah Pedals", geofex.com, 1999. See the section on the Anderton wah retrofit and the two additional schemes for voltage controllability. And the Anderton retrofit, from even earlier, published long ago in his column in Guitar Player.

Anything that varies the attenuation of the signal fed back to Q2 changes the frequency of the Vox/inductor wah circuit.

I've read the article a few minutes after creating the topic hoping that i would find some answers why no one have used this in synths but i have not really find a reason. I thought the harmonics created by the transistors and the inductor would be desired in the synth world.

[R.G.]

I think it's not used in synths because it has some fundamental problems for synth practice. Inductor based wahs have a frequency which varies with the square root of the value of the L or C which determine the frequency. In the inductor wah, the cap is electronically variable, and so you have to have huge changes in the control element to make the filter frequency change an appreciable part of the audio spectrum. For a synth, the ability to sweep most of the audio range is a huge virtue, so something like a state variable or a four-pole lowpass done with current/conductance element is a huge advantage.

The distortions from transistors and inductor might be interesting, but there are other ways to dirty up a really wide range filter. This sidesteps the issue.

[PRR]

> i have not seen a single cv controlled filter design which utilized an inductor

Design goes through fashion-phases.

The leading-edge of precision controlled processors (analog computers, also Moog/Arp synths) got into a fad of not using inductors. They are expensive, they are low-precision, they attract hum, in audio they are non-linear. "We can do better!" (True, for the reasons R.G. outlines.)

OTOH, there's seat-of-pants design using whatever is under the bench. Early Wahs. WOW it wah-wah-Works!!

> I thought the harmonics created by the transistors and the inductor would be desired in the synth world.

Synths usually start with excess harmonics. Ramp and rectangle waveforms are very rich, too rich for music (much richer than any normal musical instrument). Yes, sometimes all the harmonics are passed for that "new sound", but often the sound is band/low-passed for a more natural tone. There's other techniques (AM, FM, tracking/mixing) to richen-up synth tones in different ways. Also Portamento does something like what Wah players wish they could do, "better" ("Lucky Man" solo). What new-music fashion leader wants to sound like a 1950s Chet Atkins record?