Fuzz pot on FF behaving strangely

[Coriolis]

Hi all
I've built an FF after "Fuzz Face with Fuller mods" schem on R.G's site (guess that makes it a '69 clone). All is basically well, except for the "fuzz/attack/distortion" pot. I seem to be getting no change in the degree of fuzz, but rather it acts as a sort of volume control... got it all connected just like the schem, with a 22uf instead of the 20uf, but I can't see that making the difference.
I get a nice sound from it otherwise, the 50k bias in the input does as advertised, output pot works fine. The 1k pot after the Q2 collector (8k2) just seems to add volume, but at it's loudest setting, it does change the sound to something quite a bit nastier(if the other controls are dimed), which I like.

Overall, I'm enjoying this ckt, and getting great variation of sound, but I'm puzzled why that fuzz knob ain't working. Any ideas?

:?

c

[aron]

Weird. It should be affecting the pedal. What 8.2K resistor are you referring to?

[Coriolis]

Hi Aron!
The 8k2 is the one one the collector of Q2, but the pot I'm wondering about is the one from the emitter of Q2 to ground with the 20uf cap on the wiper.
I've never played an FF other than this, so I don't know how the range is supposed to be, but I assume it would go from no or very little fuzz, to full bore, right? It's weird...

[Coriolis]

Hmm...when I think about it, I may have been confused about the whole positive ground scheme. V+ goes to ground, right? That is, the ground coming from the input jack and going out the output jack? So + and - voltages are reversed compared to an npn circuit... or what? If I had got that part wrong, my FF wouldn't work, right?

C

[Pedal love]

Check the 1k pot to make sure it is connected properly or is working properly. The way you are describing it, it sounds as if the 22uf capacitor is shorting straight across the potentiometer. Resistance check the potentiometer.pl

[Coriolis]

Will do that, thanks!

[petemoore]

For positive Gnd, all gnds connect and go to the battery + side.
 Also the electrolytic [22uf] cap must have it's '+' side connected to ground.

[Coriolis]

Thanks for that pete, that clarifies alot. i think I got those things right on mine tho... Can anyone explain how that fuzz-control actually works? What does it affect, and what does the cap do?I couldn't read it out of the GEO FF article, but maybe thats just me...

[petemoore]

The Gain pot reduces/increases resistance from the gain stage to ground.
 At 0 resistance, anything at the 100k feedback loop is shunted directly to ground, does not pass Q1, does not collect 200$ [monopoly joke].
 As in the Sili Face, that gain pot could be a 1k or so resistor.
 More resistance to ground shunts less in the FBloop Signal path to ground 'raising' gain, changing the value of the gain pot is like having a larger fixed resistor across from the 100k to ground, measured as the R value of the pot's wafer. The overall R Value can start at 1k, I like to add a 'bump' resistor of 110 ohm or 220 ohm between the pot and Gnd. as necessary for lots of gain, a little oversaturation.
 I'll not stick foot in mouth...and not type about how the cap functions other than being a non DC path or HPass path to ground from the 100k...that's with the gain pot full on.

[Pedal love]

   
 I'll not stick foot in mouth...and not type about how the cap functions other than being a non DC path or HPass path to ground from the 100k...that's with the gain pot full on.

Clip off the 100k resistor and there is still sustain changes as the pot is rotated. Measure the resistance between 100k resistor at the base of q1 and emitter of q2 and there is no appreciable difference in resistance, as the potetiometer is rotated. The potentiometer changes ac current between q2's emitter and ground. The dc resistance change in the 1k potentiometer, used to regulate the amount of ac across the 1k of the potentiometer. If it changed dc, it would be a variable resistor arrangement. the capacitor would then be replaced by a wire and nothing more.pl

[Coriolis]

Thanks for your replies, people!
I tried bypassing the cap and just wiring the pot as a variable resistor to ground. No sound other than hum at low settings, and only clean sound at high settings (and not much gain). Just for kicks, mind you...
Then I reverted to the original wiring, and hey presto, it worked! Of course I had also been checking for solderbridges and whatnot, and I think I may have had one of them somewhere.

So now I have a working fuzz pot. It seems though, that the sound of the circuit has changed a bit, it was a bit more open before, now the fuzz is a bit harsh. Would changing the 22uf cap remedy that, or is the output cap the way to go?

Thanks again, I'll have to box it up soon and play with it to see what i wan't mod...

[petemoore]

http://diystompboxes.com/sboxforum/viewtopic.php?t=36249&highlight=ff+tweek

[petemoore]

Mine too, I just put in a 5k with a 1k across it, it measured 1.1k.
 It barely affects the gain, just more top end like the cap is seeing less resistance to the 100k [which it should be when Gain goes CW].
 THere's a reason for it, I'm sure.
 figureing it out looks like having to 'tear into' that section of the circuit.

[Coriolis]

So basically you then had a 1.1K pot instead of 1k? Still going through the cap and all?

[petemoore]

A look at Sili Face shows how the gain control is preset by a fixed 1k.
 The gain might sound good as 2k, or 1k5...depends on...what it depends on...I can't cheat and look to Joe Davissons FF Calculator though.
 I'm just about to like having the bypass cap [22uf] be 10uf [less woofy bass] and connected directly to the 100k, this gives much less gain control, but...I like the gain up high anyway.