Circuit guru's - I have an idea

[Taylogc]

Long time lurker here...have built MANY pedals over the years, thanks in part to the fine folks here -
So here goes a crazy idea -

A tremolo type effect that instead of sweeping volume, it sweeps tone

It would have a rate control and a "depth" for the frequency range to sweep
Any input on how to design a circuit to accomplish this would be appreciated

[Gus]

you mean something like a seek wha?

[Taylogc]

Not like the seek wah

Imagine that you have a simple tone control that is sweeping from the lowest frequency to the highest back and forth with the rate (speed of sweep) adjustable

It's a totally different concept than anything I can find anywhere else

[Gus]

Look up SVF

auto whas sometimes use them

They can have three outputs that can be remixed to what you like

you can sweep all kinds of things and I would guess what you are asking has been done

For the seek wha sweep the circuit instead of stepping is a possible thing to try
Sweeping a SVF is something else to try

[Taylogc]

Thanks Gus, it's a place to start..

[midwayfair]

Rob Henry (Deadastronaught)'s Light Wah project is an LFO-controlled wah, which is pretty much what you're talking about.

I made a layout for a stripped-down version of his project with just the LFO part, you might look that up. If you really want it to just be a tone sweep instead of a mid-peak sweep, you just need to leave off a few components to make it a low-pass filter sweep instead of a bandpass.

[Taylogc]

Cool - is the stripped down circuit on your webpage> and if so, what did you call it?

[electrosonic]

If you look at any envelope driven filter, you can drive it with a lfo instead of the guitar envelope.

[R.G.]

There are some ICs made for volume/tone for car radios and such that sweep the control positions based on DC voltages from pots.

Or there used to be. I always intended to do a pedal with rocker/etc. control of tone, mid, bass, and/or volume from one of these, and never got to it. They may be extinct by now. I think one part number was an LM1083 - but that's a very dim memory.

[garcho]

OTA! Ever play around with the LM13700? Try a voltage controlled filter w/lfo. There's a lot of these out there (variations on filters w/lfo). I made a BPF called Folie a Deux, schematic is bouncing around somewhere here. Similar to Anderton's.

[pinkjimiphoton]

Rob Henry (Deadastronaught)'s Light Wah project is an LFO-controlled wah, which is pretty much what you're talking about.

I made a layout for a stripped-down version of his project with just the LFO part, you might look that up. If you really want it to just be a tone sweep instead of a mid-peak sweep, you just need to leave off a few components to make it a low-pass filter sweep instead of a bandpass.

+1

[pinkjimiphoton]

13700 is perfect. real "bendy" sweetness to the way they sweep frequencies, too... can get very vowelly

[garcho]

wah anti-wah

Folie à Deux. needs a little tweaking but it works, I use mine at gigs frequently.

check out: VCFs, music from outer space, MS-20 filter, Thomas Henry's Making Music with the 3080 OTA, mutron, etc.

[Taylogc]

Thanks guys..you have all given me a direction to head...  Just looking to get outside the standard offerings and play with something unique...
This effect was proposed by a fellow guitarist and it sounded interesting to explore

[aion]

Check out the Catalinbread Pareidolia: http://www.catalinbread.com/pareidolia.html

From what I understand, it's an LFO-controlled sweep between two signals, one with bass frequencies emphasized and one with treble frequencies. Lots of videos on YouTube if you want to hear how it sounds.

The other forum has schematics, and Madbean has done some of his own research as well (check his forums).

[merlinb]

Fender produced a quasi vibrato effect that worked on a similar principle. The circuit blends between a bass-heavy and treble-heavy signal.
https://patentimages.storage.googleapis.com/pages/US2973681-0.png

Imagine that you have a simple tone control that is sweeping from the lowest frequency to the highest back and forth with the rate (speed of sweep) adjustable

Well all that would require is a conventional tone control (cap + pot) except the pot is replaced with an LDR, with an oscillator driving an LED.

[JustinFun]

I must mention the gristleizer here. The bipolar power supply and large amount of off board wiring make building it a bit of a pain in the balls but once it's done you've got a really flexible pedal with a great LFO that does vibrato and filter sweep. Descending sawtooth on the filter is a favourite of mine.

[midwayfair]

Fender produced a quasi vibrato effect that worked on a similar principle. The circuit blends between a bass-heavy and treble-heavy signal.
https://patentimages.storage.googleapis.com/pages/US2973681-0.png

AKA Harmonic Tremolo.

I think Samhay's version of the harmonic tremolo has a way to vary the width of the crossover of the sweeps, so it's another possibility for what the op wants (regular harmonic tremolo probably won't be filtery enough).

Also, an LFO-equipped Crash Sync might also work, if "plus fuzz" is an option.