PnP Fuzz Face not working properly, can anyone pls help (my voltages are listed)

[znowman]

hi, and thanks for looking, ive been trying to debug this thing myself, but as im new to this, im not sure what to try next

sound is ok when bypassed but hardly working at all when engaged, i have to play the strings hard, then i get a harsh sound (bass notes dont need to be played as hard as treble) and the sound dies very quickly (i can upload a few sound samples if that helps).

from what ive been reading and the voltages ive been checking, i think Q2 may be saturated, but i dont know how to cure it, here are the details of my build:

Ge Fuzz Face from General Guitar Gadgets.
schematic: http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_pnp.pdf             
layout/wiring: http://www.generalguitargadgets.com/pdf/ggg_ff5_lo_pnp.pdf

ive followed the project as GGG intended, except for some resistor values, which came with my matched pair of Ge's from smallbear (see below)
i also added all the optional components, except C4 (the cap for RF interference - i didnt have the correct value).
im using a wall wart, and 9.16v is reaching the board.

i purchased a matched pair of Ge's, but im using 2n3906's until i get everything working (if i do  ), i googled for the pinouts and im pretty sure i got this right.

the resistor values i got from smallbear are:

R3 - 30k
R4 - 680 ohms
R5 - 12k
R6 - 110k

these values are for the 'bear face', so i think values for the GGG fuzz face should be:

R2 - 30k
R4 - 680 ohms
R5 - 12k
R6 - 110k

----------------------------------------
transistor voltages, which are way off the guidelines in the GGG project

Q1
C = 7.78v
B = 8.54v
E = 9.16v

ive taken 2 readings for the collector and emitter at Q2 (base wasnt affected), one with the trimpot turned fully clockwise and one with it turned fully counter clockwise
Q2
C= 8.42v & 8.56 (from what ive been reading, i rekon this should be at least 1v less than the emitter)
B= 7.78v 
E= 8.45v & 8.57

---------------------------------------------
voltages at D3 are:
band end: 9.16v
non band end: 0v

----------------------------------------------
electrolytic caps:
C1 has 8.0v + and 8.5v -
C2 has 9.16v on both leads
C6 has 9.16v + and 0v -

ive spent a good while trying to figure how the circuit works, but im struggling getting to grips with positive ground.
thanks for reading (i hope ive given enough info), and any help/advice is much appreciated...

[The French connection]

Hi! Have you turn the 10k trimpot?

[Dragonfly]

to start with you have a ground problem...Q1's emitter should be 0v.

[znowman]

Hi! Have you turn the 10k trimpot?

yes, ive given 2 voltages for Q2 (one with trimpot fully clockwise and one for counter clockwise)

[znowman]

to start with you have a ground problem...Q1's emitter should be 0v.

ok, and thanks, i'll have another look (although at what im not sure)...

am i right in thinking voltage and 'conventional' current is flowing from the ground symbol on the schematic ?  and in the direction the arrow on Q1's emitter points ?   no, that cant be right if Q1's emitter needs to be 0v.   this positive ground has completely confused me, and my head is spinning - i'll have another look tomorrow

[znowman]

well i just spent a couple of hours taking readings with my meter, without achieving anything (except raising my blood pressure), i cant understand which parts of the circuit are supposed to be + or -


On the schematic, should the ground symbols be 0v ? because i thought this circuit was positive ground.

im seriously thinking of forgetting electronics and concentrating on playing more guitar

[John Lyons]

All of the ground points should be 0V
The collector voltages should be negative volts.
By turning the 10K trimmer on the Q2 collector you will be able to adjust the bias volage of Q2s collector which should be around -4.5v.
The emitter of Q1 should be directly connected to ground and all the ground points should be connected. Make sure that you follow the GGG diagram and that the red battery wire is connected to the ground of the board and that the black wire connects to the power points which are the resistors connected to the collectors and the 10K trimmer.

On your meter set it to "continuity" or "beep" and make sure that the ground points all beep when you put one probe on the battery red battery wire and the other probe on each ground point. Use the schematic and the layout for this.
Check to make sure that every solder joint is not touching where it should be and that they are bright and shiny.

Let us know what you find out. Despite the low parts count, the Fuzz Face isn't all that easy to get working.
Don't give up!!

John

[znowman]

ok, thanks for that john, and i will go through what you have said.

Make sure that you follow the GGG diagram and that the red battery wire is connected to the ground of the board and that the black wire connects to the power points which are the resistors connected to the collectors and the 10K trimmer.

i just double checked, and ive connected red from the dc jack to the ring of the input and black from the dc jack to the board at R2.
all solder joints look good/shiny, and i already checked through each joint for continuity - although my next step is to double check continuity...

i just realised something that i might have been doing wrong ,  its to do with how ive been checking the voltages.

ive been using the black lead on the negative at the dc jack (im not using a battery), and then probing with the red lead.  but i wondered if this should be reversed, and when i did that (red lead on positive at the dc jack, and probing with black), i got these voltages:

Q1
c - 1.277v
b - 0.558v
e - 0v

Q2
c - 0.599v        0.739v (2 values for trimpot CW and CCW)
b - 1.276v
e - 0.588v        0.711v

again, its the PnP that is confusing me, should i use the probe leads in the same way as an NPN circuit to take voltages ?

[John Lyons]

You will get the same voltages with either lead configuration but one way will be a positive voltage and the other will be negative.
Technically For a pos ground you want to use the red probe on the ground and black to collector/power.

Q1 looks ok but the voltages for Q2 are off. Looks for something wrong around Q2.

[znowman]

everything that is supposed to go to ground does, ive double checked all joints for continuity, ive gone through the wiring again, and ive checked there is no stray solder shorting things together, i give up...

[frankclarke]

Check pinout, metal tab = emitter, paint spot = collector.

[andrew_k]

i purchased a matched pair of Ge's, but im using 2n3906's until i get everything working

This strikes me as a possible cause of problems. Ge and Si are not that freely interchangeable. THe resistor values supplied for the GE pair are not going to be correct for the Si pair.

Also, don't be too trusting of the resistor values supplied. The pair I recently bought came with a recommended bias resistor of 11k, but to get correct bias I had to use 5.1k. I ended up just using a pot instead.

[mac]

This strikes me as a possible cause of problems. Ge and Si are not that freely interchangeable. THe resistor values supplied for the GE pair are not going to be correct for the Si pair.

Si/Si and Si/Ge FF need a 5k or so at Q2 collector while a Ge/Ge or Ge/Si need a higher resistor which increases as Q1 leakage goes up. You can exchange Si <-> Ge at Q2, but not at Q1.
Thermal runaway happens at Q1. Finger heat Q2 only and you'll notice a small decrease of Q2 collector voltage. Touch just Q1 and voltage will jump out of control.

FF DC bias

mac

[niggez]

Also try a resistor from collector to base at Q1 (I think it was 1M), that worked for me when i tried out my first germanium fuzz but only had silicon transistors to use!

[znowman]

well i'd just like to say thanks to you people who offered help, im sorry it took a while to get back to it, i really needed a break from it (for my sanity).
anyway, i replaced the Si's with the matched Ge's and its now working, i havent checked voltages yet, but the sound is fantastic...     
i now just need to trim the transistor leads, and mount everything back in the enclosure.

so again, thanks a lot for the advice, i really thought the pedal was dead