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.

 

[JohnnyCreepy]

Apart from vast amount of possible cold solder joints first thing to check is GND problem with bad contact on red circles marked. Also there’s a good change for a bridge with wiring exposed and between solder blobs. Use less flux and check your soldering station heat setting to the point where you get proper solder joints.

 

[tfTom]

Apart from vast amount of possible cold solder joints first thing to check is GND problem with bad contact on red circled marked. Also there’s a good change for a bridge with wiring exposed and between solder blobs. Use less flux and check your soldering station heat setting to the point where you get proper solder joints.

View attachment 93751View attachment 93752

Yeah I kinda rushed this since school's been eating away all of my time recently. I'll clean everything up and see if there's any change.

 

[AceHyzer]

Does signal pass through just fine in bypass?

Definitely do a thorough inspection of all the joints, looking for solder bridges that you can clean up, or cold joints you can reflow. A thorough pass through all the joints would definitely be helpful.

What temp are you running your iron at and how are you ending up with all those scratches on the board? It’s possible that you have damaged some traces in there as well. Slow and steady with the iron, especially until you’re a little more used to it, can be very valuable. It can be hard when you’re short on time!

As for q3, I don’t know off the top of my head what the voltages are supposed to be there, but it does seem plausible that there could be an issue.
What is the transistor you’re using for Q3?

 

[tfTom]

Does signal pass through just fine in bypass?

Definitely do a thorough inspection of all the joints, looking for solder bridges that you can clean up, or cold joints you can reflow. A thorough pass through all the joints would definitely be helpful.

What temp are you running your iron at and how are you ending up with all those scratches on the board? It’s possible that you have damaged some traces in there as well. Slow and steady with the iron, especially until you’re a little more used to it, can be very valuable. It can be hard when you’re short on time!

As for q3, I don’t know off the top of my head what the voltages are supposed to be there, but it does seem plausible that there could be an issue.
What is the transistor you’re using for Q3?

Bypass works just fine and is louder than the pedal signal when it's on.

My iron is at 320F, highest I use it at is 330F when I'm using solder wick. As for the scratches, I'm using my PC desk as a workspace so I don't have too much room and end up hitting the board by accident sometimes, and the lack of some helping hands doesn't help lol. Thankfully I don't think any traces are damaged since I followed the signal through every component and everything seems in order, except the whole gain loss. I will be more careful from now on though!

All transistors are 2N5088 from Tayda. Apparently for big muffs they are usually at around 4V, so there's definitely something going on with Q3. I've got some on the way, but they won't get here until next week at the earliest so I won't know if the transistor is the problem until then.

 

[JohnnyCreepy]

My iron is at 320F, highest I use it at is 330F when I'm using solder wick.

That’s crazy low temp. No doubt you get solder blobs. I run my station @ 300-350C (570-660F). Lower for components and pcb contacts, higher for wiring.

 

[tfTom]

That’s crazy low temp. No doubt you get solder blobs. I run my station @ 300-350C (570-660F). Lower for components and pcb contacts, higher for wiring.

I lied, I just realized my iron is in C not F my bad lmao

 

[AceHyzer]

I lied, I just realized my iron is in C not F my bad lmao

Leaded or unleaded solder? For Leaded that’s probably hot enough. I’ve gone to fully unleaded and I run at 705F exclusively now.

Where are you located? If you were somewhere relatively close to me I could send you a few 2N5088s to try in there. If not it’d probably be faster just to wait for your tayda order

 

[swelchy]

I run Kester 63/37 leaded solder at 380C or 716F on my soldering station..... Get in and get out.... You can see it wick in and I get out pretty quick

 

[tfTom]

Leaded or unleaded solder? For Leaded that’s probably hot enough. I’ve gone to fully unleaded and I run at 705F exclusively now.

Where are you located? If you were somewhere relatively close to me I could send you a few 2N5088s to try in there. If not it’d probably be faster just to wait for your tayda order

I'm using leaded at the moment, 63/37.

As for the circuit, I went and got some proper tools and worked on it yesterday. I think I cleaned everything up very nicely, went through every joint and fixed it up/snipped any excess solder or component legs (I didn't have flush cutters until yesterday). It's a night and day difference to my first go at it honestly. I plugged it in but still no luck.

This morning I went and bought a new transistor from an electronics store near me, threw it onto the circuit, read the voltage, but Q3 is still reading somewhere around 1 Volt. There was also no improvement with the sound volume.

 

[JohnnyCreepy]

This morning I went and bought a new transistor from an electronics store near me, threw it onto the circuit, read the voltage, but Q3 is still reading somewhere around 1 Volt. There was also no improvement with the sound volume.

Are the transistors oriented correct way? Markings on pcb may not match what’s in transistor; EBC vs CBE. If thats OK, move to check values of resistors connected to Q3/4.

 

[tfTom]

Are the transistors oriented correct way? Markings on pcb may not match what’s in transistor; EBC vs CBE. If thats OK, move to check values of resistors connected to Q3/4.

I made sure they were back when I first started troubleshooting by using other examples of the same circuit. Should I look for resistance or voltage when looking at the resistors? Do you know around what values they should be at if it's voltage I'm looking for?

 

[JohnnyCreepy]

I made sure they were back when I first started troubleshooting by using other examples of the same circuit. Should I look for resistance or voltage when looking at the resistors? Do you know around what values they should be at if it's voltage I'm looking for?

https://www.electrosmash.com/images/tech/bmp/big-muff-pi-v3-bias.png

Edit. Have you tried circuit without footswitch (board) connecting muffin pcb output straight to jack? Not so sure it could also explain transistor misbias, but low output for sure.

Also if I remember correctly on one Hizumitas/muff I built adding more resistance to R15 was needed to bias Q3&4 correctly.

 

[tfTom]

https://www.electrosmash.com/images/tech/bmp/big-muff-pi-v3-bias.png

Edit. Have you tried circuit without footswitch (board) connecting muffin pcb output straight to jack? Not so sure it could also explain transistor misbias, but low output for sure.

Also if I remember correctly on one Hizumitas/muff I built adding more resistance to R15 was needed to bias Q3&4 correctly.

I'll check the biasing once I get home later tonight. Thanks for the link

I haven't tried it with no footswitch, I'll check it out and see if it changes anything. I'll keep you updated!

 

[tfTom]

https://www.electrosmash.com/images/tech/bmp/big-muff-pi-v3-bias.png

Edit. Have you tried circuit without footswitch (board) connecting muffin pcb output straight to jack? Not so sure it could also explain transistor misbias, but low output for sure.

Also if I remember correctly on one Hizumitas/muff I built adding more resistance to R15 was needed to bias Q3&4 correctly.

I checked the biasing and voltages, something's definitely out of wack after R12. I changed R15 from 470k to 680k but Voltages are still around 1 in the entire stack. If it's not a cap issue I'm starting to think this might be a PCB problem or something.

Edit: Also tried no footswitch, but nothing really changed

 

[JohnnyCreepy]

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.

 

[Feral Feline]

As an aside, a break in the troubleshooting...

Hello everyone! I apologize in advance for this wall of text, ...

That's not a wall of text — that OP's got logical flow, coherent sentences with paragraph breaks and punctuation and everything...

You've got a lot to learn and a long way to go to get to "Wall of Text".

Thank you for not making it a wall of text.


Back to your regular-scheduled debugging ...

 

[Feral Feline]

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

 

[JohnnyCreepy]

@Feral Feline hard one, but comparing your suspected brown band to other bands I’d say it’s most likely more red than brown. Impossible to say for sure!

 

[Feral Feline]

@Feral Feline hard one, but comparing your suspected brown band to other bands I’d say it’s most likely more red than brown. Impossible to say for sure!

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.