fuzz Face Debug.... trial 2

[jlullo]

alright guys.  i tore my fuzz face apart, and put it all back together.  still having problems.  can someone please help me?

it is the fuzz face from fuzzcentral.com, no parts substitutions.

The pedal bypasses, and when engaged, it's just a slightly muffled tone... no fuzz.

I can't get the collector to bias... STILL.  no matter how i turn the trimpot, nothing happens

here are my voltages-
Q1
c  -8.96
b -4.94
e 0

Q2
c  -8.94
b -8.94
e -8.82

[albatross]

If i were you, I would get out a multimeter and test all connections, measure resistance of all resistors, to see if OK

test the trimpot resistance, and replace the trimpot if needed, if its one of them cheap metal ones from futerlec etc they are crap and prone to breaking.
test the transistors hfe etc.. Replace transistors if needed, if that dosent work check your grounding, make sure the grounds are hooked up correctly
But, as you talk about the bias voltage and the trimpot not working, i think its most likely the trimpot!

[jlullo]

albatross, that's what i was thinking... the thing is, i've tested the trimpot and it's resistance changes when i turn it.  this would mean that it was okay, wouldn't it?

how do the other voltages look to you (besides the collector)?

[albatross]

you could also just replace the trimpot with a 6k2 or 6k8 fixed resistor, i found mostly with silicon 2n3904's bc109's etc.. they bias correctly with approx that resistance.

easy to do, and guess


I dont have a fuzz face at hand at the minute as i have cleared the breadboard, so i cant help you there, but the collector should be around 4.5-5 volts

q1 emitter should be 0 i think as it connects to ground.

[tcobretti]

Is this on vero or pcb? 

If it's vero the very first thing I would do is look for solder bridges between two tracks.  You can use your multimeter to help find continuity where there shouldn't be any.  Then I would multimeter every component you can to make sure it's the correct value.

If it's a PCB the process is much the same, but the likelihood of solder bridges is somewhat less.  I'd still check every resistor to make sure it is the correct value, and I'd check for continuity where there should be none.

Another question that occurs to me is whether you have your transistors oriented correctly.

You have read the what to do if it doesn't work thread, right?

[jlullo]

tcobretti,
this is on pcb... i've already checked all of the resistors and checked for solder bridges- everything checked out.  I'll go back over them again, though.  My transistors are also oriented correctly..

[bluesdevil]

Which layout did you use? I found errors in the Dragonfly "Boutique '69" pcb when I tried to build from it.

[jlullo]

bluesdevil,
it was the layout from fuzzcentral.com

[bluesdevil]

ah, sorry..... you said what layout in the initial post. After reading everything better, my guess is that you have a short at the trimpot between the -9v line and Q2's collector. Also weird you're getting full voltage on Q1's collector (shouldn't the 33k bring it down a bit?).  I would double check to see if the trimpot is soldered into the pcb correctly. Should have the left and middle lug soldered together on the pcb pads going to Q2's collector and the right leg on the pad going to the 470 ohm resistor and .01 capacitor.
     The suggestion to just use a 8.2k in it's place is not  bad one in case there is something screwy with that trimpot anyway.
     

[petemoore]

  I'd just measure the actual resistance across Q2's collector resistor, in circuit.
  Then measure everything else too.

[jlullo]

i'm going to try a new pot right now... if that doesn't change anything, how do i position the fixed resistor on the board?  just one lead going to the collector, and the other going to the cap/resistor?

[joegagan]

whatever it is you are doing it over and over again.
You consistently have been reporting nearly full batt voltage on the collectors since about 1996 ( kidding)

there is a major flaw that  is overly simple you are overlooking i think

[jlullo]

whatever it is you are doing it over and over again.
You consistently have been reporting nearly full batt voltage on the collectors since about 1996 ( kidding)

there is a major flaw that  is overly simple you are overlooking i think

haha tell me about it!  that is definitely what i'm thinking as well.  this is now the third time i've taken this apart and rewired.  exact same result every time. I've swapped out parts, checked parts, checked for soldering bridges, checked my wiring.  The only thing that it could be is that i am doing something correct, when it obviously isn't.  I just don't understand why it's only effecting this whole collector bias process.  i'm mean, what the hell could it be?

i appreciate you coming back to take a peep at my debug marathons, joe; even though i'm sure you can predict what my results are

[joegagan]

i think you might be grounding your opamp pins to your flux capacitor

[guitar_199]

I just want to draw attention to two things in particular that might help to focus your investigation.

Q1 - if it is a PNP, it's hurting.... and I mean severely.    With the emitter hard grounded and -4.94v that thing ought to be biased on hard/  In a typically biased Ge PNP you should only see about -0.2 to -0.3 or so.  So something is definitely wrong in here.

Q2 - assuming it is a PNP..... it looks as though something is wrong with the emitter's path down to the fuzz pot.   If the emitter had a path to ground, the -8.94 on the base would never reach that high....rather it would bias the base on, collector current would start to flow, the voltage at the emitter to gnd would be a lot lower and the collector voltage would come on down as well.

Just some ideas....

Bob

[petemoore]

  A fuzz Face has a buncha stuff gotta be exaclty replicated, counting the # of connections at each node and visually or DMM verifying each one has the right number of connections on your board..
  The transistors and caps [any polarized] have to be right way around.
c  -8.96
b -4.94
e 0

Q2
c  -8.94
b -8.94
e -8.82
  Not that hooking up the 'other lead' of the DMM matters if the polarities are correct [what the circuit sees]...all these voltages are of the negative variety, I therefore assume it's because:
  The leads on the DMM...red went to ground or..
  The circuits power supply polarity is reversed or...
  This is a PNP Pos Gnd FF were talking about..
  3 options, perhaps you can sort them all out, I can't, I didn't see a schematic in relation to your build, nor transistor types used, perhaps I missed where this debugging information dwells, but it all matters.

[jlullo]

Pete,
Sorrry about that.  I had made a post about this before, and i completely forgot to copy the info over from the previous.  This is a positive ground version, and i got matched transistors from smallbear (2n1305's).  Unfortunately, Fuzz central didn't post a schem of their layout on the site, but here is a link to the layout

http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacelayout.png