Mudbunny trouble shooting

[jtn191]

I feel like I can get this: I used an audio probe to trace through the PCB and the last place I'm hearing signal is on one leg of C3. Do you think C3 is bad?

fyi: I don't have any diodes in the circuit yet and Q2's collector voltage looks really low: 1.37 v
thanks

[mgwhit]

Could be.  Is it an etched or a fabbed board?  If it's an etch, I'd look for a short before I swapped out the component.  Good luck!

[jtn191]

it's fabbed but I took the suggestion anyway and found a short from the sustain pot to gnd! I'm getting signal now and it seems to be responding to controls but there's not much volume on tap...the collector of Q2 is still suspiciously low. voltages:

Power supply: 9.5 v

(collectors of)
Q1  4.59
Q2  1.37
Q3  4.39
Q4  3.98

hm...I read on diystompboxes that Tri-muff's Q2 biases at 1.22 V because they lack the R9...maybe this isn't a problem. But way less gain and volume than I was expecting

[jtn191]

bump.
I'm getting sound but no distortion. Seems to be a problem with Q2.

[gtr2]

Do you have a schematic with component values?


Josh

[mgwhit]

Based on the previous posts, I assumed it's a Mudbunny built to Triangle specs.  I'd help with the Q2 voltages, but mine is VRH specs and has the R9 that is omitted in the Triangle version.

[jtn191]

Matthew's right, Josh, it uses the same component values that are listed in Madbean's doc for Triangle specs.
I read somewhere that because of the missing R9, Triangle Q2's bias lower. I put diodes in and it's still clean. Right now, I'm only hearing the filtering effects: tone knob, bass cut on input, mids knob. It seems like it's right around unity gain or a bit below.

I've just been audio probing and I found something peculiar: of the 3 lugs on the sustain pot, I can only hear signal on lug 3--and it's LOUD.

[jtn191]

Aha! it was a bad pot. I was recycling EHX pots and something must've gone wrong in desoldering it from the board. I replaced it and now it sounds rad!

[mgwhit]

Cool?  Glad you got it working.