Help! Debugging Big Muff build

[blakkwater]

Hey all,

I'm currently working on a big muff build and I'm totally baffled as to why I'm getting virtually no sputtery fuzzy goodness. The pots are doing pretty much nothing, across the entire sweep for all three of em. When I dime all the pots, i get a hair more "overdrive", if you could even call it that, than when I have all the pots zero'd. Speaking of which, even with the volume pot zero'd it still has only very very slightly less volume than when it's maxed. I'm still working from a breadboard cuz I wanted to make sure it worked before I put it into a stompbox enclosure.

This is the circuit I'm using:


Here are the voltages I'm getting

Battery: 8.82V

Q1: 2N5088
C: 3.91V  B: 0.63V  E: 0.05V

Q2: 2N5088
C: 3.92V  B: 0.63V  E: 0.05V

Q3: 2N5088
C: 3.82V  B: 0.62V  E: 0.05V

Q4: 2N3904
C: 4.14V  B: 0.05V  E: 1.01V

Diodes are all 1N4148
1st gain stage:
D1 Anode: 0.40V  Cathode: 0.63V
D2 Anode: 0.63V  Cathode: 0.40V

2nd gain stage:
D3 Anode: 0.40V  Cathode: 0.63V
D4 Anode: 0.63V  Cathode: 0.40V

Before putting in the 2N5088s, I had a quad of 2N3904s but the problem as I described was worse. The 5088s helped, but only VERY VERY VERY slightly.
Here's what it looks like currently. A godawful mess, but I have checked it ad nauseum and it follows the above circuit EXACTLY.


Please help me!! 

[aron]

I would listen after the 1uF caps (after the collectors) and make sure that you have an amplified signal. Also verify that the pots are grounded. It makes no sense that having them at zero vs. max produces similar sounds.

[hannibal827]

Q4: 2N3904
C: 4.14V  B: 0.05V  E: 1.01V

This is the problem, right here.  The base of your Q4 is all but grounded.

My BMP build follows the same schematic, and my Q4 voltages look like this:
C: 3.9V
B: 1.8V
E: 1.2V

If you audio-probe the circuit [listen after the 1uF caps], you should probably find that you have a decent signal until you hit Q4, at which point you are probably losing it at the base, where almost all of it is going to ground.

I would check the resistors there, and/or try a different transistor.

[blakkwater]

Well I checked everything and wiggled the resistors and transistors yesterday and some voodoo happened and now it works fine! Thick, sputtery, nasty, filthy fuzz. I love it

I think I'll replace that 3904 when I mount all the components to a perfboard though, just to be safe.

Thanks for the help guys!