Mini Fuzz Face Troubleshoot

[kitedude18]

Hi guys,
Currently coming to the end of my mini Fuzz Face build, however i'm facing a few problems.

First things first, here's a link to the project instructions and schematics http://pedalparts.co.uk/docs/FuzzFace-Mini.pdf (i'm building the BC108 NPN version) using this daughterboard for switching http://pedalparts.co.uk/docs/3PDTDC.pdf

I initially had problems in the way that I could only get any fuzz when I played really really hard. This led me to think I had a biasing problem. I noticed that I had in fact used a 33 ohm instead of 33K ohm resistor in R2, which would obviously mess with Q2.  So I replaced R2 with the correct value resistor (actually a 22K in series with two 22K in parallel giving a total of 33K, as I had no 33K lying around).

I also noticed that the bias pot was not working properly, so replaced that with a known working pot (50K instead of 47K, still inside designers specs)

My transistor readings when connected to ground are:

Q1 Collector:  6.7V   Base: 5.4V   Emitter: 0V (As expected as it runs straight to ground, continuity verified)
Q2 Collector: 6.07V Base: 6.68V  Emitter: 6.02V 

Q1 seems ok, however using my audio probe on the collector gives a clean signal, then probing on either of the other legs gives no signal.

I know that Q2 should have a collector of around 4.5V according to the instructions (page 3 bottom right hand side), and I know that the collector value should be greater than the base and emitter voltages.

Can anyone make any recommendations as to what to try next please?

  Thanks

[Electric Warrior]

Q1 is far from ok. The collector should measure between 1.2 and 1.4V with silicons, base around 0.6V.

[kitedude18]

Ah, I assumed because the relative readings were where they should be that it was ok. What would you suggest be my first line of action with this?

[Electric Warrior]

basic trouble shooting: find your mistake.

[kitedude18]

Turns out Q1 had failed internally, thus sending a large amount of current to Q2 and saturating it leading to the lack of output. Quick replacement and it worked straight away

[PRR]

> used a 33 ohm instead of 33K

With 33K, about 8V/33K= 0.25 milliAmps flows in R2 and into Q1C Q2B.

With 33 Ohms, about 8V/33= 250 milliAmps (0.25 AMPS!) flows in R2 and into Q1C Q2B.

The transistors are NOT good for a Quarter AMP of current.

You might wash your dog with a 1-inch water hose. If you tried it with a 30-inch water Main (1,000 times as much water), you'd blow the pooch a mile out into the woods.

Easy to note the difference between garden hose and city water main. Resistors all look alike. You need to read the part, and it is wise to double-check on your meter, and double-double-check that you see the Ohm/K/Meg marker on your meter. (Sighing over how many times _I_ have made similar mistakes.)

FYI:

> Q1 Base 5.4V  Emitter 0V

That's a base-emitter voltage of over 5V. Transistor Vbe can NOT be over about 0.6V, 0.7V, rarely (not in pedals) 0.9V. If it is, that transistor is blown. (Or you have mis-read the pin-out.)