Debugging a heavily modded fuzz face

[kin0]

Name of the project: Fuzz Face (with a lot of mods)





Mods are listed in the schematic

It makes no noise at all. I still haven't wired up it all the jacks and the 3pdt switch (I bread boarded all things beside the circuit itself and the potentiometers). Besides I've already built 2 pedals with the same schematic and layout and they worked fine.

Q1
C = 0.7V
B = 0.02V
E = 0V

Q2
C= 0.18V
B= 0.7V
E= 0.17V

From the pedals that I've already built (which I don't have anymore) these should be the values:
Q1
C = 1.45V
B = 0.64V
E = 0V

Q2
C = 6V
B = 1.8V
E = 1V

[midwayfair]

Q1
C = 0.7V
B = 0.02V
E = 0V

Q2
C= 0.18V
B= 0.7V
E= 0.17V

From the pedals that I've already built (which I don't have anymore) these should be the values:
Q1
C = 1.45V
B = 0.64V
E = 0V

Q2
C = 6V
B = 1.8V
E = 1V

Neither set of voltages looks right. Q1 should settle around .5v. The first thing I'd do is set the tight trim to 50K to normalize that. But that shouldn't result in no sound regardless.

I don't see anything obviously wrong in the schematic or layout, so I'd start checking your connections (with the multimeter's continuity setting -- don't guess or trust your eyes) and looking for solder bridges.

Does your bias trim do anything?

Did you check the pinouts?

[LucifersTrip]

the 2nd set of voltages are actually OK for silicon.   you can check out GGG:

Q1
Collector
1.4v
Base
0.6v
Emitter
0.0v
Q2
Collector
4.5v
Base
1.4v
Emitter
0.8

but yes, as midwayfair wrote, there's def a wiring, soldering or component error. did you have it working on a breadboard first? 

[PRR]

Open-circuit between Q2 C and the +9V.

Follow that path with voltmeter, see where voltage changes suddenly from 0.17V to 9V.

[kin0]

I bread boarded the first fuzz face I built to see if the mods work but I didn't think it was necessary this time as well. The bias pot allows you to get a dying battery sound  (and it does nothing happens when I twist it). The pinouts are right. As for the path between Q2 and +9V, the wire connecting the +9V and the tone pot got disconnected. After I connected it back these are values:

Q1
C = 1.35V
B = 0.4V
E = 0V

Q2
C = 8V
B = 1.35V
E = 0.75V

The values seem ok now but I checked and there is still no sound

[LucifersTrip]

8V is a bit high for a FF, but it seems you have narrowed it down to the off-board wiring

[kin0]

8V is when the bias is at max (so I can lower it). The problem is that still don't have any off board wiring. I wired in in/out and power jacks to a box which I use to check the board before putting it in a box. Or do you mean the potentiometers by the off board wiring?

[LucifersTrip]

off board includes everything not on the board itself...switches, pots (if not soldered to board), jacks, etc.

[kin0]

Oh okay, I will check the pots and switches

[kin0]

Checked them and everything is fine from an unknown reason the Q1 base measuring is back to around 0.05V, so I guess the problem is in that area. I can't find anything wrong. I start to suspect that the transistor maybe just no good

[Digital Larry]

Battery is backwards in your schematic.

[kin0]

oops, but in the layout you can see that it is placed the right way

[kin0]

Replaced the q1 transistor now the base is 0.4V, still a bit low but much better. I shall check if it works later today

[kin0]

Still no sound 

[PRR]

> Q1 base measuring is back to around 0.05V, so I guess the problem is in that area.

No, the problem is that Q2 is not getting power. (When it does, it raises Q1 Base to around 0.6V.)

Ditch the "adjustable bias" stuff and use known-good values for Silicon NPN fuzzface. Do you get reasonable voltages and yowsa sound?

[kin0]

Still no sound but the voltages are:
Q1
C = 1V
B = 0.3V
E = 0V

Q2
C = 7V
B = 1V
E = 0.4V

[LucifersTrip]

Still no sound but the voltages are:
Q1
C = 1V
B = 0.3V
E = 0V

Q2
C = 7V
B = 1V
E = 0.4V

looping (change 8v to 7v)
http://www.diystompboxes.com/smfforum/index.php?topic=103548.msg923257#msg923257

edit:
also, try taking the signal right off Q2C with a cap in series. it is also a possibility you have an open connection between Q2C and the off board wiring.