Diy Fuzz face problem

[Fossilshark]

Im new here, and I recently got some ac128s so i built a fuzz face. I checked everything twice and i cannot get it to work right. The sound clip is running straight into my diy tube amp with the pedal running off 9v. Please let me know if you need more information


https://youtu.be/y2rw_uG49Uc

[Ben Lyman]

Welcome Fossilshark. Sounds like a bias prob. Try replacing the 8k2 with a 10k pot to adjust the bias.
Just use one of the outer lugs and the middle lug wired in series so you can go from 0k to 10k and everything in between

[Fossilshark]

It kinda worked. When the pot is on 0 ohms i get a decent amount of fuzz but i dont think its working right. Turning the resistance up even a little cuts volume completely (on the bias pot). I should mention my input cap is 2.2uf and my fuzz cap is 22uf but i dont think that matters much

[Ben Lyman]

no, those caps are fine. a common mistake is to accidentally use a 470k instead of a 470r, double check that one

[Fossilshark]

Nope, all resistors seem correct

[Electric Warrior]

Could you measure the voltages between all transistor leads and ground with all stock resistors, please? That may tell us where the problem is.

[Fossilshark]

Q1
BC = .072v
BE = .079V
EC= .151V

Q2
BC= .091V
BE= .151V
EC= .054V

Pins referenced to ground

Q1
B= .08V
C= .15V
E= 0V

Q2
B= .149V
C= .054V
E= 0V

This is with the new bias pot set to 8.2k like in original schematic

[Electric Warrior]

Something is wrong with Q2. With Q1C sitting at 0.15V, Q2C should measure around 8V. Maybe you misidentified the leads or the emitter is shorting out with ground?

[antonis]

<This is with the new bias pot set to 8.2k like in original schematic>
Bias pot should be 1k at its maximum setting..

Maybe you've tangled Collector & Emitter resistors..

[goo]

replace 33K with 50K trimpot (lugs 2 and 3 should be soldered together to get full "50K") and replace 8K2 with 10K or 20K (i recommend 20K) trimpot as well (solder lugs 2 and 3 as well).
some transistors are hard to bias by original fuzz face schematic.

[Electric Warrior]

<This is with the new bias pot set to 8.2k like in original schematic>
Bias pot should be 1k at its maximum setting..

Maybe you've tangled Collector & Emitter resistors..

Right.. maybe the bias pot wasn't set correctly. Put the 8.2k back in and check if the voltages are as expected.

0.15V is rather low for Q1C and I'd expect it to sound farty or gate a little, but it shouldn't be as bad as in the clip.

replace 33K with 50K trimpot (lugs 2 and 3 should be soldered together to get full "50K") and replace 8K2 with 10K or 20K (i recommend 20K) trimpot as well (solder lugs 2 and 3 as well).
some transistors are hard to bias by original fuzz face schematic.

When they don't bias right they probably leak too little or too much. Easy to make up for by tweaking that 33k. I'd leave the 8k2 alone. Too much resistance there will cause volume issues.

[goo]

When they don't bias right they probably leak too little or too much. Easy to make up for by tweaking that 33k. I'd leave the 8k2 alone. Too much resistance there will cause volume issues.

sometimes 8K2 is not enough and trimpot helps. especially if you want some spitty-gated (to taste) sound. you can always tweak trimpot to 8K2, or more (less volume, more spitty-gated-fuzz), or less (more volume but less fuzz, yeah).

[Electric Warrior]

You could dial in the spittyness on Q1C as well. I find too many options overwhelming and like to keep it simple. 

[goo]

You could dial in the spittyness on Q1C as well. I find too many options overwhelming and like to keep it simple. 

agree. Q1C is good option too. 

[pinkjimiphoton]

from the sound of it, your transistors are backwards. if socketed, switch 'em around. a reverse beta'd ge will still work, but sound really buzzy and farty and spitty. its common for them to work better one way than the other.

in every case i've encountered its ended up being a pinout problem when you get "that sound". you can bias it into working if ya have it at an extreme of range.

jmo... ymmv some ge's are so leaky you can literally reverse them and they will work the same.  some times they seem to work backwards better. socket 'em before ya solder 'em.