Fuzz Face - Q2 collector voltage...

[eddie83]

Hey guys, sorry for the repost, the previous one was a bit too long, decided to post a clean one for easy reading...

This's my first stompbox project and i decided to build a PNP/+ve gnd fuzz face, schematic link attached.
http://www.generalguitargadgets.com/diagrams/fuzzface_sc_pp.gif

The problem with it now is that the output's gated, only the louder tones are heard, the softer ones are muted. I've recorded the voltage readings with my analog multimeter, tried my best to get the most accurate reading here:

Q1: E/0v      C/-0.25v   B/-0.06v
Q2: E/-0.1v   C/-0.11v   B/-0.25v

Now, the problem's with Q2's collector lead, which is far away from the ideal -4.5v... Can anyone advise me on what might be causing the problem above?

btw, i've changed some of the resistors values according with the one small bear sent me for my matched Ge transistors:

R2:39k
R3:150k
R5:3.9k

before the change, i used the original values in the schematic and the gating effect was already there...

thanks for all ur help ppl...

happy new year!

[birt]

put a trimpot in there. fuzzfaces, rangemasters... need some fooling around before you get the desired voltage

[Johnny Guitar]

I'm surprised no one more knowledgeable than me has answered this yet, but when I got to this forum a few months ago it was due to similar problems with a few FF circuits I was building -- I now think that the FF is probably not a very good choice for a first, second or third stompbox project.

Anyway, I too had used Steve's (from smallbear) resistor values in my circuit and (IIRC) had a problem much like what you are describing. No offense to Steve but I would use his values as more of a starting point or ballpark figure.

I ended up replacing two of the resistors with trimmers of approriate values to tune in the bias properly. I doubt I will ever buid a FF that doesn't have trimmers again (unless I prototype it first with trimmers and then measure the proper resistance needed).

I'm doing this from memory but IIRC I changed out the 33K with a 50K trimmer, and changed the 8.2K to 25K trimmer and it quickly gave me the wonderful FF sound that I was hoping for. The following hour or so that I spent with subtle tweaking was more seeing how far I could push the extreme end of full fuzz level.

BTW, make sure your pot is wired up correctly. I had mine backwards so when I went to turn the fuzz (which had not been behaving that imppressively) "down," it went almost chaotic -- at that I moment I though, "OK, this is good!"

Good luck!
John
You beat me birt! :oops: Your answer wasn't up yet when I went to post. Good on you.

[Fret Wire]

Your voltages are too low. Try leaving R5 as is and lower R3 back to 100, R2 down to 33k. but you may have a soldering problem there. Go over all you soldering work with a magnifyng glass, and check for broken traces, and bridged solder joints.

[petemoore]

Some of the R values can be read in Cct.
 If a lower value is indicated during testing with DMM, could be the current is flowing around the other way through the circuit, mapping may help, I've done math and found bad Resistor or Mis-R values this way.
 If transistors can be pulled, it's easy to see if there's single path through the resistor or alternate path[s.
 Without 9V Power
 Check all ground points. Check for NoN-continuity between transistor legs and other places where no connection exists.
 Check for continuity of battery clip  +/_ to Circuit board +'s and _'s. Check for NoN-continuity between battery + and _ ....with these low voltages, also check for  resistance between battery + and _.
 Transistor pinouts
 Cap orientation
 I think of every way to apply the DMM using continuity checker, resistance ranges, and Voltage. Rarely do I even set it for current readings, but with low voltage readings your'e getting, massive current could pull the voltage down, might be worth a current check there.
 I forget exactly, FF should be less than 4 ma I think.
 Sometimes I check battery voltage with and without circuit connected to it.