How to build a Feedback switch? (Think Caroline Guitar Wavecannon "Havoc"))

[pnadora]

Hallo pedalbuilders :)

I really like the "havoc" switch in the demos of the Caroline Wavecannon, or the fuzzrocious oscillation modes. Are they seperate "feedback"-circuits that go on top of the pedals, or are they fundamentaly integrated into the pedals designs? I am wondering if it would be possible to at such a "go crazy" button to a random gain pedal. Maybe someone has a schematic for the Wavecannon that can clear things up?

Thanks!

[Beaker]

You can do it to many dirt pedals - EHX Big Muff is one example. It's really easy - take a feed from a transistor and re-introduce it back into the circuit earlier in the signal chain.

Here is another I stumbled on by accident:

Conrad Buzztone and Volume Expander

[pnadora]

Thanks a lot! I am planning to build an OCD with feedback like this one:

https://www.youtube.com/watch?v=8kXhaQT1k2I

Would the potentiometer that "controls" the feedback just be a variable resistor in the feed from one of the transistors?

[Beaker]

Again, I am not familiar with this pedal, but listening to the linked demo, it sounds exactly like the feedback switch I added to the Conrad Buzztone.

"Would the potentiometer that "controls" the feedback just be a variable resistor in the feed from one of the transistors?"

Yes, you've got it.

Adding the pot will allow you to vary the amount of feedback into the circuit. I don't think it is needed, I would just use a SPST momentary footswitch, but you might find it beneficial. Try it and find out for yourself.

Let us know how you get on.

[M. Spencer]

Do any of you know if this feedback loop is what is happening in the Red Witch Fuzz God's secondary stomp switch?

[pnadora]

Hey, it is me again :) Thanks for the tip with the buzztone.

The OCD turned out great, but I still have problems with the Feedback mod.
I get signal cancelling and a deep pulsing when pressing the switch. :/

Do you know if the OCD changes the phase? I connected row 10 on the left side with volume 3 on the version 3 layout from here:
http://tagboardeffects.blogspot.de/2012/02/fulltone-ocd-all-versions.html
So the input after the first capacitor with the output of the pedal before the volume knob (like you did on the buzztone). Is there a place in the circuit that is pre/or post phase reversal, so that I could just create a "smaller" feedback loop that is in phase?

If you or anyone else had an Idea that would be great!

I will experiment with some placements for the loop and write again if I find something new out! :)

Happy new year btw!

[Beaker]

Happy new year to you too!

I can't really help I'm afraid, as I have not built an OCD before.

What you need to do is go into "Circuit Bender" mode, and sit with the pedal turned on and passing signal but keep your volume low! Now use a jumper wire as a touch probe, to connect different points of the circuit.

You need to be looking at the schematic to see what is going on.

 https://guitar-gear.ru/forum/index.php?app=core&module=attach§ion=attach&attach_rel_module=post&attach_id=7175

I would be looking to try connecting pin 7 of the IC, (or try the volume pot), to a point back earlier in the signal chain, for example pin 3 or on Q1 or Q2, and see what happens.

It's just a case of trial and error really, but try and work logically and in sequence. Hopefully you will be able to find the best points to connect, that will produce the desired effect, but with no unwanted side effects.

Good luck, I hope this helps!

[pnadora]

Problem solved!

I just went in front of the first capacitor, straight from the Input of the board to volume 3. I am not sure If the capacitor does something to the phase (is there like a 90° phase lag on a cap??) so maybe in your circuit the total number of phase-lagging/shifting worked out after the cap and on the ocd you get a perfect result just going input to output. :)

Super happy now with my build :D
Here is a photo of the finished pedal. I cannot show the inside unfortunatelly since I use old daddario packages to "isolate" the board from the enclosure and I dont want to open it^^ Should have taken a photo before assembly!

EDIT: Forgot to rotate the image, but I guess it works that way too^^

[Beaker]

Good work, that looks really nice.

I'm glad you got it sorted.