Tenebrion Freak-Out Switch

[Aleph Null]

I've built the Tenebrion stock with a long brick. I love that I can get it to just barely self oscillate. I would like to add a momentary foot switch to allow me to push it into self oscillation, but I'm not quite sure how to implement it. Would it be as simple as shorting past R11, or from L3 of the "feedback" pot past R11?

Here's the schematic for reference:
https://dl.dropboxusercontent.com/u/28586266/GCFX%20Build%20Docs/TenebrionBuildDoc.pdf.

[Jebus]

Hello!

R11 sets the minimum resistance in the feedback loop. By shorting that you would get self oscillation or not depending on the position of the feedback -potentiometer.

Shorting from lug 3 of feedback to R11 is a viable option, but in that case you need to put couple of capacitors to both sides of the switch to block DC-component (which would cause popping). 100nF is used to block DC from the feedback -potentiometer, so that would be a good size. I would probably add a trimmer in series with the momentary switch so you could "tune in" the oscillation.

[Boba7]

What I did for a friend of mine is put a momentary switch that shorts pin 2 and 3 of the mix pot or the feedback pot (select one or the other with a dpdt). I lowered R11 too, I think to 12 or 15k

You could even chose both pots with a momentary dpdt for full on mix and feedback!
(then with 2 dpdt you could select full mix on or off and full feedback on or off).
Unsure if silent momentary dpdt exist...

[Aleph Null]

Jebus: Thanks for the insight; I was wondering what C7 and C8 were doing!

Boba7: I like how simple shorting the pot legs would be, but I also like the idea of having the swell speed tied to the feedback setting in some way.

I'll have to do some testing to find what I like, but thanks to you guys I have a clear path forward:

Plan A: Use a momentary switch to bypass R11 or add a resistor in parallel and use the feedback knob to control swell speed.

Plan B: Use a momentary DPDT to short lug 2 and 3 of the feedback pot, and to add a pot in parallel to R11 to control the swell speed.

I'll be sure to report back once I've had a chance to experiment a little.

[Aleph Null]

I finally got around to doing some testing.

The feedback and reverb pots, as well as R11 all play a roll in getting the circuit to self oscillate. I found that grounding lugs 2 and 3 on the feedback pot as well as shorting past R11 was enough to get a reliable feedback swell. The speed of the swell can be controlled with the reverb pot; pretty much anything above nine o' clock will self oscillate. I tried shorting the reverb pot and controlling the swell with the feedback pot, but this didn't provide as wide a range of swell times.

Given how much the reverb mix effects the swell times, I don't think a dedicated "swell" pot is necessary. Feathering the freakout switch should be enough to control the oscillation. If I change my mind later, I'll just add a internal trimmer that can be switched on in parallel to R11.

I found a momentary DPDT switch here. http://www.mammothelectronics.com/4SFS2PDT-MS-p/800-1001.htm

[Aleph Null]

Another update: I ended up adding a 25k trim pot that is parallel to R11 when the freak out switch is engaged. The speed of the swell is still very interactive with the Mix control, but now I can fine tune it for my pickups, playing, style, and needs.