Big Muff Pi not working At all

Started by Keef30, May 27, 2005, 08:42:41 PM

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Keef30

So I just attempted to build my first real pedal (built an extremely simple boost pedal before succesfully).  I got the schematics for the big muff pi at fuzz central.  I used transistors from Radio Shack (high gain npn's) that were supposedly comparable to the 5089.  All connections seem to be fine (everythings grounded that should be, etc.).  When I plug it in I get nothing but Spanish-speaking radio.  I measured power on the following.

Q1:

C=0.75

B=.05

E=.05

Q2:

C=0.75

B=.05

E=.05

Q3:

C=4.43

B=.66

E=.02

Q4:

C=1.78

B=2.40

E=1.72

D1:

A=.75

K=.49

D2 (same as D1)

D3

A=4.42

K=4.07

D4(same as D3)

I Also built the audio probe from this site and was able to hear signal until I got to the first trannie (not very long), when I got there I could very faintly hear it, but it was also mixed with the radio sounds i spoke of earlier.
Not sure, but it seems to me that somethings up with the power not being distributed properly, as I would assume the voltage on the transistors should be a lot higher.  Or could it possibly be that the transistors used are just not compatible?  Ive re-traced the circuit compared to the schematic several times and checked the board for any bad solder bridges and everything seems to be as it should, so now im clueless as to what to do.  This was done on perfboard too.  I hope this is enough info for someone to theorize as to what the problem is...Ill be happy to supply anymore info if it helps.  Battery measurement 8.68 at the board.  Thanks.

aron

Your collector voltages are way too low. Somehow you have something wired  incorrectly. I assume the battery is around 9V right?

Keef30


Keef30

well, i think i may be on the right track...i rotated all the trannies so the pin orientation is opposite of what it was and now i can at least here the tone knob and possibly the distortion levels being effected by turning the pots (while hearing spanish radio), but there is obviously a grounding issue or something.  at one point i was able to hold the pots in my hands a certain way and actually hear the input signal, but it only lasted a few seconds and i couldnt figure out how to fix it...now i cant recreate that.  checked all my ground connections several times....stumped.  the collectors are definitely measuring much higher voltage now.  it seems at this point theres just a really simple connection im missing somewhere as i was able to hear my source audio for a second.

aron

Measure the voltage at the junction of your V+ and the collector resistors - it should your max V+.

Also go and check that all your grounds are good by using the continuity checker.

Build an audio probe to listen through your circuit and find where the signal is stopping.