replacing the feedback resistor in a fuzz face with a pot

[mordechai]

I want to have a 100K pot in the place of the 100K feedback resistor.  I wired a pot into this position, putting jumpers from lugs 2 and 3 into the respective pads of the PCB I'm using.  It works and varies the sound in an interesting way, but when I max the pot out, the signal goes dead.  How can I prevent this from happening? 

[LucifersTrip]

I want to have a 100K pot in the place of the 100K feedback resistor.  I wired a pot into this position, putting jumpers from lugs 2 and 3 into the respective pads of the PCB I'm using.  It works and varies the sound in an interesting way, but when I max the pot out, the signal goes dead.  How can I prevent this from happening? 

with a small resistor in series

[Derringer]

if you have a dmm, check your bias as you vary the feedback resistance ... it will change

so you may want to include an external bias pot as well so that you can tweak the bias (by ear) around the different settings of feedback resistance

[R.G.]

Feedback happens in both DC and AC varieties. The FF has a combined AC + DC feedback resistor.

You *could* leave that 100K alone and put a 100K pot in series with a 10uF capacitor in parallel with the existing 100K feedback resistor. That would let you change the AC feedback while leaving the DC one alone. Note that this would vary the AC feedback in a way to reduce gain, not increase it.

Another way to approach this is to split the 100K AC + DC feedback resistor into two 51K resistors in series, and then use a 10uF (or so) capacitor to ground in the middle of them. This shunts all the AC feedback to ground, and removes the AC feedback entirely, raising the gain to its maximum possible. Now you can put a ... um, maybe 1M pot in series with a 10uF DC blocking cap in parallel with the 51k/10uF/51k DC feedback. This will let you vary the AC feedback to get more gain all the way to much less gain.

[mordechai]

RG, I've used a smaller value feedback resistor (47K) and the circuit seems to have more gain as a result, or at least it seems that way to my ears.  And I am interested in coaxing more gain out of it, so I thought that I might just wire a 100K pot in the place of the feedback resistor to be able to adjust.  But what if I were to just put the small cap in series with that pot -- would that still work and manage to stop the pot from cutting the signal totally when maxed out?

[joegagan]

see the wooly mammoth. chuck zwicky designed it.

[mordechai]

Joe, I just looked at the Woolly Mammoth and saw what you're talking about.  What is the purpose of having lug 2 of the pinch pot going through the cap into the fuzz pot?  How does this affect the fuzz level/signal as opposed to being disengaged so that the pinch pot just controlled the feedback resistance but did not have lug 2 linked to the fuzz pot?

[Mark Hammer]

see the wooly mammoth. chuck zwicky designed it.

That's exactly what I was going to suggest (minus the part about Chuck, because I did not know that).  What I like is the manner in which the feedback pot and gain pot interact to produce a broad array of flavours.