Feedback loop on a Rullywow King Tut?

[ThurberMingus]

I am building a King Tut and I really wanted to add a momentary feedback loop to it. I was wondering if the process is the same as adding a feedback loop to other muff circuits by connecting the emitters from Q2 and Q3 or if there is something else I need to do.

Then I would have it wired up to a normally open SPST stomper right?

Thanks in advance!

[midwayfair]

You're presumably talking about a "positive feedback loop" -- the pedal has several feedback loops, but they're all negative!

To get positive feedback, you need two signals that are in-phase to link to each other in a feedback loop.

A transistor stage inverts the signal at the collector; your signal is in phase at the emitter. In this pedal, there are FOUR total inversions from your input signal, one at each collector.

Your signal is in phase at the following places:

Input, collector of Q2, collector of Q4 (and consequently the OUTPUT of the entire effect), Q1 emitter (not much good to tie that to the input, FYI), and Q3 emitter.
Q1 collector, Q3 collector, Q2 emitter, and Q4 emitter.

Knowing this, there are a few places where you could create the loop, depending on what you want it to do. If you want to be able to control the howl with your volume and tone controls on the guitar, you'll need to connect the input to one of the amplified in-phase spots described above.

If you just want it to howl and do basically the same thing regardless of where your guitar knobs are set, you'll have to use any two of the above in-phase spots and just connect them through a capacitor to a switch with a resistor or pot. Keep in mind that it can also change things depending on how much amplification you have on the "later" side of the loop. Connecting your input to the emitter of Q1 isn't going to do much if anything even though they're in-phase because the emitter isn't amplified, but tying the emitter of Q1 to the collector of Q4 DOES work and gets you the most amplification in the feedback loop while not directly interacting with your guitar.

[ThurberMingus]

So instead of a straight wire connecting the two points I need a cap and resistor on either side of the switch? Any values in particular I should use?

So with the knowledge of which points work, could I just run a loop through the circuit, and use a wire with a cap and resistor to connect the points so I could get an idea of sound without soldering anything in, right?

Thanks for the advice Midwayfair, you're always so nice and helpful! Reminds me that I need to spend more time on here!

[midwayfair]

If you're connecting the input and output you don't need a cap -- it's already decoupled. You need the cap it you're using any of the other points so you don't upset the dc biasing.

[selfdestroyer]

Are you trying to do the mod that is listed here?
http://rkerkhof.ruhosting.nl/Taas/Mods/Big%20Muff.htm

Cody

[ThurberMingus]

Yes, that's the one I was referencing.