fuzz factory mod question

[EATyourGuitar]

I just ordered a pcb from mad bean for the zombii aka fuzz factory. I have read about changing the input and output caps for more bass. I will probably try that. the other mod I want to do is inspired by Mark Hammer's post about adding a cap to ground on the emitter Q2 on a muff fuzz aka muff overdrive. the fuzz face has an electrolytic 20uf cap to ground with a 1k pot on the emitter of q2. the fuzz factory is based on a fuzz face according to zvex. I'm looking at the muff fuzz, pnp fuzz face, npn fuzz face, fuzz factory schematics side by side. I'm understanding some parts of it. I'm really lost as to where to put the added fuzz pot on the fuzz factory. I dont know if it goes on Q2 or Q3 and if its on the collector or emitter. should I use a 20uf electrolytic? a 10k pot maybe to match whats already on the fuzz factory. so a 10k and 20uf or 47 uf electro at the collector of Q2 or Q3 in the fuzz factory should do it right?

last question, is it pointless to add clipping diodes to ground with a switch after the vol knob before the output cap?
zombii schematic pdf

[joegagan]

not sure the mod mark is tlaking about, but the fuzzfactory already has the control i think you are talking about on Q3.  you could try a gain softening mod on Q2, an old gus smalley fuzzface trick from the mid 90s. this would be a trimpot or pot between q2 emitter and the stab. this might cause static sound, not sure.

the input and output caps are fine, it is the .1uf at base of q2 that limits the low end in the factory. put a 3.3uf, or even 10 uf on a switch and listen to the difference.

if you are looking to increase the flexibility of the factory, turn the 220k input resistor on Q1 base/coll junction into a pot. works beautifully. a 250 k will prob work fine if you don't have 220k handy.

[EATyourGuitar]

I think I figured out what I was trying to do. looks like the drive knob in the fuzz factory = fuzz knob on a fuzz face. I wasn't expecting it to be on the top in the schematic. but Q3 Coll in the zombii is the same as Q2 coll in a NPN fuzz face. there is an electrolytic there. on the fuzz face its a 1kB in series with a 20uf electro to ground. on the zombii, its a 10k pot in parallel with another 10kB pot in series with a 10uf electro from V+. but it is pnp so if you think about it. the PNP fuzz face also has the electro on V+ or +G. maybe I can try different electros for C3 in the zombii.

not sure the mod mark is tlaking about, but the fuzzfactory already has the control i think you are talking about on Q3.  you could try a gain softening mod on Q2, an old gus smalley fuzzface trick from the mid 90s. this would be a trimpot or pot between q2 emitter and the stab. this might cause static sound, not sure.

yeah thats what the comp knob does on Q3. so it would be comp 1 and comp2. for Q2 and Q3. that might not be worth adding a knob. thanks for the idea though.

the input and output caps are fine, it is the .1uf at base of q2 that limits the low end in the factory. put a 3.3uf, or even 10 uf on a switch and listen to the difference.

zvex actually suggested changing the in and out caps to get more bass on his forum. I was just reading through some old posts. it also says you can change the in and out caps on the zombii build doc to 20uf and 47uf. I will try it your way too. I'm sure there are a few ways to do it, each with their own sound.

if you are looking to increase the flexibility of the factory, turn the 220k input resistor on Q1 base/coll junction into a pot. works beautifully. a 250 k will prob work fine if you don't have 220k handy.

wouldn't adding a 250k pot on base/coll Q1 cause Q1 to loose its 4.5v at the base. doesnt that just decrease headroom/volume and add clipping?

anyway, this is just a smaller part of a bigger pedal that has a LPB boosting the fuzz factory through a 25k pot in series to change the impedance. thats why I asked about putting clipping diodes at various stages. it will have 7 knobs, maybe 4 switches, and 2 footswitches.

[joegagan]

yeah, controlling gain through the 220k resistor may not be the most elegant way to control the grit,, but the factory isn't exactly an elegant pedal. that mod works well for me.

i forgot to put in my first post, i like your idea of clipping diodes to ground at the end of the circuit. there is plenty of gain in a factory to get them cooking. why didn't i think of that?

[EATyourGuitar]

I think I'm gonna try your idea with the base coll 250k pot. then its got 8 knobs and thats really what I'm shootin for.

[joegagan]

go for NINE!  you won't regret it.

the above mentioned .1 cap mod can be best on a pot. graft in the tone control from an EZface - a 100k pot in series with a  3.3 ( or 10 uf ) this  assembly parallels the existing .1 cap at base of Q2 in da factory.

[EATyourGuitar]

so its basically the stock 100n cap when the tone control is rolled to one side. that makes perfect sense. I'd rather have it on a knob anyway.

I used a resistance calculator to figure that a 1.9M resistor in parallel with a 250k pot on the base to  coll of Q1 will give it a range of 0k to 220k. I could even put the 1.9M on-board. this thing is gonna be sweet. I found the 1590DD will fit it.

[EATyourGuitar]

ok so now that I have built it I want to share what I learned about the mods mentioned in this thread.  look at the easy face schematic again. the tone control should probably be 50k instead of 100k. you can hear the middle settings of the tone sounding muffled or slightly muddy. in the fuzz factory, I think that cap between Q2 and Q3 would be better on a rotary switch. the second mod was the grit control. thats just putting a 220k pot instead of a 220k resistor on Q1. it doesn't change the sound much until you get to zero Ohms where the base is right on the V+ rail. but it is interactive so it can be useful to tweak the gate, comp stab a little bit. the grit knob is loud through half the range and starts to drop in volume sharply about half way up. then it just mutes everything. if I build another one, there are a lot of things I would do differently. I think the in and out caps could go on the same switch. I have clipping diodes on this one but they are after the volume knob. it would be great to use the old vol knob as a gain control for clipping and put a 100kA or 50KA after the out cap. I'm not really sure whats up with the output shunt. is that part of the filter? or is it pop protection? and what values should I use for the two volume pots?

EDIT: I just looked at the easy face schematic and thats actually not how I did my tone control. I messed up. I put lug 2 going to Q3 and lug 3 had a 100nf wile lug 1 had a 3.3uf poly