GGG Fuzz Face Almost No Output- Desperate for help

[nicholasvbest]

Hey guys. Bought a GGG fuzz face that I cannot get to work. Almost no sound comes out until I strum real hard.

GGG Fuzz Face Schematic
Fresh battery measures 9.25V

Q1:
c: 1.34
b: 0.62
e: 0

Q2:
c: 9.15 (sweep max range .10V)
b: 1.34
e: 0.84

D3:
a= 0
k= 9.24

I added some optional mods (e.g. optional trimmer in R5, R1 switching "pop" eliminator, C4 RF interference eliminator, C6 power filter, D3 reverse voltage protection)

FF uses 2N3904 NPN transistors on a negative ground pedal

The issue: the Fuzz Face sounds plenty fuzzy, but only if I hit the strings hard enough. Until then, there's no sound from the FF side, like some crazy gate or something. I'm told this is a transistor issue, and I bought new transistors and reflowed their sockets to no avail... also built an audio probe to find that I can only seem to hear my "unaffected" guitar signal at one side of R2, and no signal at the other side of the resistor. Resistor value checks out, reflowed the resistor as well.

At a total loss. Can someone point me in the right direction? Many thanks

Some Pics

[antonis]

also built an audio probe to find that I can only seem to hear my "unaffected" guitar signal at one side of R2, and no signal at the other side of the resistor.

Can't get your definition for R2 "sides"..
If you mean lower & upper leg, then you're OK..
(signal should appear on lower leg where not on upper leg - battery is considered as AC Ground..)

Signal should be continued to Q2 Collector which DC value should lie in a much lower than battery's value..
(about halfway of it..)
I suspect some short around R4, R5, Q2 Collector & Battery..

You may verify GGG FF working voltages here: https://www.diystompboxes.com/smfforum/index.php?topic=104888.0

[willienillie]

What value is your trimmer?  Can you post pics?

[bushidov]

It does sound like a "transistor issue". It might be that you have the pinout rotated 180 degrees. The transistors "work", but barely. You typically have two camps of pinouts:
1. 2N3904/2N5088 style
2. BC547 style



I don't see the PCB pinout/BOM that is specifically called out, so I cannot verify against what you have vs what should be there.

[Electric Warrior]

also built an audio probe to find that I can only seem to hear my "unaffected" guitar signal at one side of R2, and no signal at the other side of the resistor.

Can't get your definition for R2 "sides"..
If you mean lower & upper leg, then you're OK..
(signal should appear on lower leg where not on upper leg - battery is considered as AC Ground..)

Signal should be continued to Q2 Collector which DC value should lie in a much lower than battery's value..
(about halfway of it..)
I suspect some short around R4, R5, Q2 Collector & Battery..

You may verify GGG FF working voltages here: https://www.diystompboxes.com/smfforum/index.php?topic=104888.0

This. The other voltages look spot on. It's just Q2c that is off. If it's not a short, maybe the trim pot is not wired correctly?
With Q1C at 1.34V, Q2C should be around 3.1V with stock values according to the muzique.com calculator (but of course it can vary - if you take 20% tolerance for the pot into consideration, it can be quite a bit higher or lower):



http://www.muzique.com/lab/fuzz_face.php

[nicholasvbest]

What value is your trimmer?  Can you post pics?

Hi again, it's me with the dual build. 10k trimmer. How easy is it to "fry" a trimmer" ?? I soldered it on almost flush to the PCB, minus 1-2mm
Some pics

[nicholasvbest]

It does sound like a "transistor issue". It might be that you have the pinout rotated 180 degrees. The transistors "work", but barely. You typically have two camps of pinouts:
1. 2N3904/2N5088 style
2. BC547 style



I don't see the PCB pinout/BOM that is specifically called out, so I cannot verify against what you have vs what should be there.

Hi, thanks for bringing this up- the pedal uses 2N3904 transistors, I've updated the post.
To dispel any doubt, I bought some extra 2N3904's and tried them in Q2 in every possible configuration with no success

[nicholasvbest]

If it's not a short, maybe the trim pot is not wired correctly?
With Q1C at 1.34V, Q2C should be around 3.1V with stock values according to the muzique.com calculator (but of course it can vary - if you take 20% tolerance for the pot into consideration, it can be quite a bit higher or lower):

http://www.muzique.com/lab/fuzz_face.php

Thanks for the resource! I saw it and wasn't sure how to use it- I'll be sure to refer to it as I go through troubleshooting.
The trimpot will only fit in one orientation, I might have to try removing it and putting in the stock 8.2k resistor

[antonis]

Thought we're talking about GGG FF.. Now we're talking about a FF / Rat combo..

If you please, post particular schematic of your build..

edit: Don't bother.. Just realized it's build on seperate PCB..

[nicholasvbest]

If you mean lower & upper leg, then you're OK..
(signal should appear on lower leg where not on upper leg - battery is considered as AC Ground..)

Got it, thanks. Yes i meant the lower leg. I have a lot to learn about pedal circuits it seems...

Signal should be continued to Q2 Collector which DC value should lie in a much lower than battery's value..
(about halfway of it..)
I suspect some short around R4, R5, Q2 Collector & Battery..

This is driving me up a wall! Just to be clear: I'm checking for:
1. Stray wires (checked with my eye/tools to check false contacts)
2. Poor solder connections (checked with continuity testing from connection to connection, reflowing solder joints?)
3. Faulty components (checked with various component specific testing techniques- resistors, caps, pots, transistors)
Rinse and repeat? Not sure where to learn to follow my circuit to get any useful information from my audio probe

[antonis]

Have you got a DMM..??

[nicholasvbest]

Have you got a DMM..??

Yessir!

[antonis]

Now we're talking..

Set it on Resistance measurement range..
Place one lead on Q2 Collector and hold it there..!!
Place the other lead on R5 upper leg (junction of R5,R4 & C3).. Take masurement.. If it's inside R5 value range remove it to R4 left leg and take another measurement.. If it's inside R4+R5 range, Q2 Collector resistors are OK and you'll have to deal with Q2 as sole device..

Edit: What i'm trying to tell you is: Q2 Collector voltage staying on PS value may be due either short of Collector resistor(s) or Q2 misbiased (transistor at cut-off region..)

[nicholasvbest]

Place the lead on R5 upper leg (junction of R5,R4 & C3).. Take masurement.. If it's inside R5 value range remove it to R4 left leg and take another measurement.. If it's inside R4+R5 range, Q2 Collector resistors are OK and you'll have to deal with Q2 as sole device..

Thanks, that's pretty insightful, I'll keep that in mind going forward, I get too frazzled trying to look at the circuit like that..

I did the check and got 0.9k at the junction (R5 is 1k), and 1.23k at the "left" leg of R4 (R4 is 330ohm)
So it seems to check out. And now we would say that my resistors are functioning as they should, and also that my transistor is not inherently busted?

[antonis]

Hmmm.. Not quite..

DC voltage drop (from +9.25V to Collector voltage) should be about 200mV  (0.84/1k x 1k23) which is close enough to your readings..

May I ask you the reason for such a low value of R5..??

[PRR]

I think trimmer R6 is "infinity" (not connected or bad-busted).

With R6 at infinity the circuit gets happy with very-very-little current in Q2, very teeny voltage drop in collector resistor, Q2 working like a 1-legged jogger.

Ohm meter, Q2 Emitter to ground. If it is not 1K, tack a 1K fixed resistor there and re-check. If it now works smooth but small, tack the 10uFd across the 1k, it should be FUZZ. To get in-between, figure out what's wrong on R6.

[nicholasvbest]

Hmmm.. Not quite..

DC voltage drop (from +9.25V to Collector voltage) should be about 200mV  (0.84/1k x 1k23) which is close enough to your readings..

May I ask you the reason for such a low value of R5..??

Sorry, the schematic I posted uses R5 as a single resistor. However, the GGG mod I opted for in the circuit was adding a trimmer (called R5T), and the value is 10k. In addition to this trimpot, there is another resistor called R5 that's in series (??) with the trimmer that has a 1k value. This is shown in the FF Wiring Layout

Edit: replaced the 10k trimmer and 1k fixed resistor with a single 8.2k resistor, but left with the same situation. The resistance readings on the R5 and R4 legs we talked about still check out though

[nicholasvbest]

Ohm meter, Q2 Emitter to ground. If it is not 1K, tack a 1K fixed resistor there and re-check. If it now works smooth but small, tack the 10uFd across the 1k, it should be FUZZ. To get in-between, figure out what's wrong on R6.

Thanks for the feedback- I'll have to tackle this after my exam, but you're saying I should check resistance between Q2 emitter and ground, if it's not 1k then add a 1k resistor between the emitter leg and its place on the PCB? and if that works with muted results, add a 10uFd cap in parallel with the resistor?

And if this works, then I know R6 is the problem?

[Electric Warrior]

Hmmm.. Not quite..

DC voltage drop (from +9.25V to Collector voltage) should be about 200mV  (0.84/1k x 1k23) which is close enough to your readings..

May I ask you the reason for such a low value of R5..??

Sorry, the schematic I posted uses R5 as a single resistor. However, the GGG mod I opted for in the circuit was adding a trimmer (called R5T), and the value is 10k. In addition to this trimpot, there is another resistor called R5 that's in series (??) with the trimmer that has a 1k value. This is shown in the FF Wiring Layout

Edit: replaced the 10k trimmer and 1k fixed resistor with a single 8.2k resistor, but left with the same situation. The resistance readings on the R5 and R4 legs we talked about still check out though

Are you saying you replaced the trimmer and resistor with a single 8k2 and you're still measuring only 1k in circuit? That's odd..

[nicholasvbest]

Are you saying you replaced the trimmer and resistor with a single 8k2 and you're still measuring only 1k in circuit?

Ah, my mistake for being unclear. Between Q2 collector and the junction of R4, R5, and C3, I get a resistance measurement around 7.4k, and at the far leg of R4 I get just under 7.4+330k= ~7.7k.

Now that I'm checking it, I'm getting almost 9k and 9.3k with the multimeter leads swapped (negative/common on Q2 C, pos on resistor)... does this make sense to y'all? It doesn't to me

Btw, can't thank everyone enough for your help and advice... this was a decent investment for me and I've been really anxious to play the thing, its been incredibly frustrating to not get it in working order