PLEASE HELP!! Fuzzhead

[erynforrester]

Gentlemen,

I'm hoping this is a simple fix.

I've built a fuzzhead as my first build. although I haven't build pedals I've built amps and have a basic understanding of electronics.

Built the fuzz head with internal trimpot.

Used offboard wiring on this website.

bypass mode works normal,
when effect is engaged it is dead.
I built a second board and dropped it in in case it was a component fault or something, and same thing.
-checked each component with ddm prior to soldering

voltages for transistors are as follows

Q1 - AC127
c: 32mV
b:83mv
e: 29mV

Q2
e: 3.67V
b: 4.23V
c: 9.07V

Q3
c: 8.67V
b: 3.6V
e: 3.2V

Q4
e: 3.34V
b: 3.72V
c: 9.07V

I'm new to this but the Q1 voltages seem way too low. I've checked and checked the orientation of the transistors and the'yre right according to any info I can find online.


Would greatly appreciate any help or suggestions.

Have tried re-flowing, cutting/filing between tracks.

The first board had the same voltages as well.
thanks in advance guys

[IvIark]

Yes Q1 seems to be the problem.  The collector is connected to the supply via the trimmer and a 1K resistor in series so if you're still only getting a mv voltage at the collector when the trimmer is at a minimum then there is probably a bad solder joint at the resistor and/or trimmer, or maybe an incorrect value has been used.  They're almost certainly the problem parts in some way so that's the area to check

[erynforrester]

ok, progress.

you were spot on. The IK resistor was one row too short, so not in series with the trimpot.

I've fixed that and now have 8V on the collector of V1.
however, b and e are still only 87 and 85 mV.

do you know roughly what they should be?
thanks again

[erynforrester]

I fixed the 1K resistor on the original board and we now have fuzz..
I should be able to debug the other from here.
thanks again

[IvIark]

Probably OK for the emitter I would have expected the base to be a little higher maybe.  Are you getting anything out of it now?

[erynforrester]

Hi Mark,
bit of a late reply, but just wanted to say thank you for the help.

I now have one brilliantly working fuzz, and one that's half way - (fuzz isn't there, gain pot working in reverse but volume pot working normally) I may just build a new board.

Learning heaps, I've pinched some thinner gauge solder from work which melts quicker so the connections are smaller - less chance of bridges etc.

I've got some stand alone pins for transistors now, so much better prepared for the next build.

thanks again,
what an amazing resource you have built
keep up the good work.

regards
Eryn