SOLVED PedalPCB Green Russian Big Muff Output Issue

[tfTom]

Hello everyone! I apologize in advance for this wall of text, but I want to be as thorough as I can. I am building my second pedal ever and I've gone through quite a bit of a hassle trying to troubleshoot it. The main issue I've had with the pedal is the output volume is very low. It's way quieter than the clean bypass signal. All knobs seem to function properly, the output is just really low.

This was my first time ever troubleshooting a pedal, so I tried doing my research first, but I'm pretty stumped at the moment. I made a quick audio probe and looked around the circuit, everything seemed to work perfectly until I reached R12 on the circuit. On one side, the signal was pretty loud, but on the other it dropped down dramatically, I'm not entirely sure how much it is supposed to drop since R12 is a limiting resistor from what I have gathered, but it did seem like a very big drop in volume.

After the audio probe I decided to check the voltage for each of the Transistors as well as R12, so here is the list.

Q1
Collector - 4.61
Emitter - 0.14
Base - 0.7

Q2
Collector - 3.78
Emitter - 0.07
Base - 0.62

Q3
Collector - 0.4
Emitter - 0.38
Base - 1.04

Q4
Collector - 4.46
Emitter - 0.94
Base - 1.43

R12 went from 3.78V to 1.04V

I'm pretty sure there's something going on with Q3, I'm not too sure if its fried or if the resistor has something to do with it, but I don't have a spare to test the circuit with a new one. Any pointers are appreciated. Thank you!

I attached some pictures of the (sloppy) solder job i did, there are a few scratches on the back of the board but I'm pretty sure it's all cosmetic. There's also quite a bit of flux residue that I haven't been able to clean off entirely.

 

[Nic]

I just zoomed in on the band in question as far as "enhance" would go, and I agree — looks reddish on closer inspection.
I previously was just comparing it to the other bands' hues, but not all bands are created equal, nor colour-keyed to the Pantone scale. Or any scale.

I see the 2nd band purple ... brown pruple black red brown. 17k ?

 

[Feral Feline]

I see the 2nd band purple ... brown pruple black red brown. 17k ?

2nd band from bottom looks purplish, but the 2nd band from the top is definitely red on my recently replaced and re-calibrated monitor.

That's the thing about second tier bands, the headliner-bands always sabotage the opener's sound...


OH, and if R15 was 17k and the circuit worked, it would provide GOBS-O-GAIN!

 

[Nic]

Here's a pic of mine that's really sounding fantastic to my ears and others at least.

I took it under good lighting so you can compare it with yours ?

 

[Nic]

2nd band from bottom looks purplish, but the 2nd band from the top is definitely red on my recently replaced and re-calibrated monitor.

Definitely red 2nd from top... but surely no 1.2 gigaohms

 

[tfTom]

You changed R14 instead R15, but that’s not the culprit here. I’m wondering why some of the e-caps are subbed with other types?

C5 and C8 are there to block DC so maybe replace those with e-caps? If you don’t have 47nF ones, use two 100nF parallel to get close or use what ever you have -/+20% of suggested value.

R15 looks to be incorrect:1k2.
That would explain a lot. Here's what colours, using DigiKey's resistor colour calc, I'm seeing for it:
BROWN BLACK BLACK RED BROWN = 11k
Reading it opposite direction:
BROWN RED BLACK BLACK BROWN = 1k2

Either way, that's not the spec'd value for PPCB's GREEN RUSSIAN.

R12 could be suspect, too — if read backwards it could be 120Ω instead of the correct 10k.
Double-check R12, but I think R15 is the culprit.

The other resistors when reading the colour-codes backwards give funky non-realistic values, so I think they're okay.


Left to right of all the resistors as on the board relating to Q3...

REFDES	R15	R16	R12	R13	R14
PPCB's GR SPEC	12k	390Ω	10k	100k	470k
ON THE BOARD	1k2 or 11k	390r	10k or 120r ?	100k	470k

View attachment 93902

Hello everyone, it's been a busy weekend at work so I haven't been able to work on the pedal until today. I do have some good news for you though! I'll make a separate reply to this post explaining everything.

 

[tfTom]

Hello everyone, it's been a busy weekend at work so I haven't been able to work on the pedal until today. I do have some good news for you though! I'll make a separate reply to this post explaining everything.

While I was doing my initial research a while back, I came across some discussion posts talking about how some programs could be used to simulate circuits and test pedals before they actually took the time to build them. I decided to look into this, so I built the schematic from the PedalPCB documentation for the pedal onto a program called LTspice. After a few hours of tinkering around, replicating it, and getting it to finally work as intended, I noticed that in the program you can import certain parts from real manufacturers into the pedal. I tried best matching what the schematic called for into the program and noticed that the circuit in the simulation worked with ceramic caps. As soon as I realized this, I got right to work on the actual pedal and changed every electrolytic 0.1uF capacitor to a ceramic type, and it worked! I'm not too sure if one of the caps that was on there was bad, or if it was just the wrong type of capacitor for the circuit, but once I plugged everything in, the pedal worked as it should. I've been trying to troubleshoot this for a while now so I was very happy to finally have a functioning pedal. I want to thank you all for the help, I really do appreciate it .

 

[tfTom]

While I was doing my initial research a while back, I came across some discussion posts talking about how some programs could be used to simulate circuits and test pedals before they actually took the time to build them. I decided to look into this, so I built the schematic from the PedalPCB documentation for the pedal onto a program called LTspice. After a few hours of tinkering around, replicating it, and getting it to finally work as intended, I noticed that in the program you can import certain parts from real manufacturers into the pedal. I tried best matching what the schematic called for into the program and noticed that the circuit in the simulation worked with ceramic caps. As soon as I realized this, I got right to work on the actual pedal and changed every electrolytic 0.1uF capacitor to a ceramic type, and it worked! I'm not too sure if one of the caps that was on there was bad, or if it was just the wrong type of capacitor for the circuit, but once I plugged everything in, the pedal worked as it should. I've been trying to troubleshoot this for a while now so I was very happy to finally have a functioning pedal. I want to thank you all for the help, I really do appreciate it .

Anyway, here's pictures of the final product!

It's my first time trying 3D printed stencils so it's a bit janky but I'll get better at it over time ;P
Right now I'm just happy it works. Again, thank you all for the help, you guys were awesome.

 

[AceHyzer]

Rock on dude! Glad it’s working. Be sure to set the status of the thread to Solved and enjoy your new pedal!

 

[JohnnyCreepy]

Glad you got it work! Where you bought e-caps and what brand they were?

If you have component tester, you can measure how leaky caps are.

 

[giovanni]

You changed R14 instead R15, but that’s not the culprit here. I’m wondering why some of the e-caps are subbed with other types?

C5 and C8 are there to block DC so maybe replace those with e-caps? If you don’t have 47nF ones, use two 100nF parallel to get close or use what ever you have -/+20% of suggested value.

Capacitance adds up in parallel. You want series.

 

[giovanni]

The type of cap shouldn’t affect the proper functioning of this circuit. You may have had a faulty cap somewhere or desoldering all caps and resoldering fixed some cold solder joints.

Congrats on the working pedal and welcome to the forum!

 

[JohnnyCreepy]

Capacitance adds up in parallel. You want series.

Call me serial failer.

 

[tfTom]

Glad you got it work! Where you bought e-caps and what brand they were?

If you have component tester, you can measure how leaky caps are.

They were Chang caps from Tayda, not too sure if they were already broken or if it was something I did that messed em up. Unfortunately I don't have anything to test them with so I don't really know what's up with them.

 

[Feral Feline]

Probably just a cold solder-joint somewhere.

I'd keep the old caps, you can use them to breadboard something simple to test them, then re-use the good ones in future builds.
Or you can make art with them...