Butt Head Pedal Not Working Correctly

[greypilgrim76]

Hi All,

So out of the dozen or so PedalPCB projects I've built in past few weeks, all of them are working perfectly, except for the Butt Head pedal. The way that it's not working has me scratching my head, though, so I thought I'd post here and see if anyone has any ideas on where to even start. (Honestly, I'm leaning toward just ordering a new PCB and rebuilding it, but maybe some of you folks have more experience with this sort of issue than I do.)

So the pedal "works," in the sense that the indicator LED is functioning correctly, the bypass mode sounds fine, and the effect clearly "kicks on" when I press the switch. The problem is that it just sounds terrible, and the knob functions are out of whack. Here's the list of issues I'm noting:

1. Volume drops precipitously when engaged. Like, even with the Volume knob up all the way, it's barely at parity.
2. The Grunge knob doesn't introduce any distortion. It sort of just acts like another volume knob, but it gets sort of muffled as it's turned clockwise.
3. The High knob doesn't appear to do much of anything.
4. The Low knob does increase the low end notably, and it also increases the overall volume.

I'm pretty clueless as to what the issue might be. My soldering looks good to me, but here are some pics of the board, in case anyone sees anything I'm missing, either with assembly or components:


It may be that this sort of issue isn't really solvable without hands-on access, but I figured it couldn't hurt to ask. If anyone has any troubleshooting workflow suggestions, or recognizes the issue and its possible cause(s), I'd love to hear it.

Okay, I promise this is my last help request for a bit!

Thanks!

 

[greypilgrim76]

No tone from either leg of C8 (especially the R10 side of the component) seems suspicious if you say R10 is fine, both legs of R10 are fine? I would check continuity between all nodes at that junction (C7, R11, can be used/checked also etc) Also be aware when you are checking, you can check by trying to touch the pad (hard of course with solder on it, but can poke around at different areas of the joint), and you can also check by touching the lead of the component, a bad solder joint

Yep, both legs of R10 have strong tone. C7 has no tone, but R11 has tone on one side. I'm not sure what that info would show, but that's what I found.

 

[greypilgrim76]

Another update in addition to my last two response posts: I spent the last few hours at the workbench with two goals: first, to explore what might be going on around C8 and IC1.1, and, second, to probe the full audio path. On the first front, I started by reflowing C8, but that didn't change anything--still no audio tone at all on either leg of the capacitor. Then I moved on to reflowing the IC socket for IC1 (with the IC removed, of course). After reflowing the socket and reinstalling the IC, the behavior was the same--no tone on legs 2 and 3, and a much weaker tone going out of the IC on leg 1 than coming into it from leg one on IC2 and R10.

At this point, I wasn't sure if there was something wrong with the capacitor I was using for C8 or the socket for IC1, so I carefully desoldered both and replaced them with brand new components. (No lifted pads--itself a small victory!) I also replaced the actual 4558 IC with a fresh one. With everything replaced and resoldered, I got the exact same behavior I noted originally with C8 and IC1. So, with nothing else obvious going on there, I went ahead and traced the tone through the rest of the audio path with my audio probe. From leg 1 of IC1 forward, I didn't find any components with notable tone absence or change at any point, so the only points in the whole audio path with behavior that seems incorrect to me are C8 and IC1.

I even plugged the pedal back into my amp and played through it, and I got the same results that started the whole process: the LOUD and LOW knobs both increase volume, and when either is turned down all the way, there's no signal going to the amp. (This seems normal for the LOUD knob, but not for the LOW knob?) The HIGH knob doesn't appear to do anything regardless of position, and the GRUNGE knob increases the volume and low end somewhat when turned up, but doesn't introduce any distortion into the circuit.

At this point, either something's going on that I'm not even aware I should be looking/testing for, or else something's wonky at C8/IC1 that's persistent even after replacing those components.

The only questions I have at this point, just to make sure I'm focused on the right spots, are 1) should I be getting tone from both legs of C8? And 2) should the tone going out of leg 1 of IC1 be louder than the tone coming out of leg 1 of IC2? If the answer to both questions is "yes," then something's obviously wrong there, but I don't know what would be going on that would persist across a total component swap.

I don't have a clear idea of where to go from here or what else to check, but (at the risk of sounding like a broken record), I'm open to suggestions! Could there be something going on with the pots? Or something non-PCB related? Is there some really basic thing that, as something of a noob, I might be overlooking entirely?

Sorry for the short novel--just wondering if I've reach the end of the troubleshooting road. Thanks again for all the continued suggestions and support!

 

[jimilee]

Another update in addition to my last two response posts: I spent the last few hours at the workbench with two goals: first, to explore what might be going on around C8 and IC1.1, and, second, to probe the full audio path. On the first front, I started by reflowing C8, but that didn't change anything--still no audio tone at all on either leg of the capacitor. Then I moved on to reflowing the IC socket for IC1 (with the IC removed, of course). After reflowing the socket and reinstalling the IC, the behavior was the same--no tone on legs 2 and 3, and a much weaker tone going out of the IC on leg 1 than coming into it from leg one on IC2 and R10.

At this point, I wasn't sure if there was something wrong with the capacitor I was using for C8 or the socket for IC1, so I carefully desoldered both and replaced them with brand new components. (No lifted pads--itself a small victory!) I also replaced the actual 4558 IC with a fresh one. With everything replaced and resoldered, I got the exact same behavior I noted originally with C8 and IC1. So, with nothing else obvious going on there, I went ahead and traced the tone through the rest of the audio path with my audio probe. From leg 1 of IC1 forward, I didn't find any components with notable tone absence or change at any point, so the only points in the whole audio path with behavior that seems incorrect to me are C8 and IC1.

I even plugged the pedal back into my amp and played through it, and I got the same results that started the whole process: the LOUD and LOW knobs both increase volume, and when either is turned down all the way, there's no signal going to the amp. (This seems normal for the LOUD knob, but not for the LOW knob?) The HIGH knob doesn't appear to do anything regardless of position, and the GRUNGE knob increases the volume and low end somewhat when turned up, but doesn't introduce any distortion into the circuit.

At this point, either something's going on that I'm not even aware I should be looking/testing for, or else something's wonky at C8/IC1 that's persistent even after replacing those components.

The only questions I have at this point, just to make sure I'm focused on the right spots, are 1) should I be getting tone from both legs of C8? And 2) should the tone going out of leg 1 of IC1 be louder than the tone coming out of leg 1 of IC2? If the answer to both questions is "yes," then something's obviously wrong there, but I don't know what would be going on that would persist across a total component swap.

I don't have a clear idea of where to go from here or what else to check, but (at the risk of sounding like a broken record), I'm open to suggestions! Could there be something going on with the pots? Or something non-PCB related? Is there some really basic thing that, as something of a noob, I might be overlooking entirely?

Sorry for the short novel--just wondering if I've reach the end of the troubleshooting road. Thanks again for all the continued suggestions and support!

Did you check all your resistor values to make sure they were all the right values? Forgive me, that’s a lot to go back through and read.

 

[greypilgrim76]

Did you check all your resistor values to make sure they were all the right values? Forgive me, that’s a lot to go back through and read.

No worries! I'm definitely aware that this thread is getting out of hand. But yeah, I've rechecked all of the resistor values and cap values, and I've also tested all of the ones that can be tested while soldered to the board. If there's an issue with a component at this point, it's a problem that can't be easily verified, with the exception of the weirdness going on with C8 and IC1.1.

 

[jimilee]

What are your voltages on IC1? I don’t see them listed, forgive me if I overlooked them.

 

[xconverge]

What are you using for your tone? is it musical or a single frequency? The reason I ask is because I want to know if the tones you are hearing on IC1 and other places are noise/something else that just "sounds like something", or the actual input tone you are passing through the audio path.

You should get the exact same tone output at leg 2 of R10 (which you say is good), leg 2 of C7, leg 2 of R11, and leg 2 of C8, they are all directly connected via traces with nothing in between/around them. Is it possible when you did this https://forum.pedalpcb.com/threads/butt-head-pedal-not-working-correctly.28405/page-3#post-369790 you lifted a pad or broke the trace on leg 2 of R10? I would check continuity between the same spot you are touching on R10 for tone with the #2 legs of C7, R11, C8. If continuous, then I am very confused, if not continuous, you could try tacking a piece of jumper wire onto the blob of leg 2 of R10 to any of those other 3 spots I keep mentioning.


I am hung up on what you are seeing between R10 and C8 and don't want to move farther down the audio path until I feel like the input/output at C8 are good and match what you hear on leg 2 of R10.

 

[greypilgrim76]

What are you using for your tone? is it musical or a single frequency? The reason I ask is because I want to know if the tones you are hearing on IC1 and other places are noise/something else that just "sounds like something", or the actual input tone you are passing through the audio path.

You should get the exact same tone output at leg 2 of R10 (which you say is good), leg 2 of C7, leg 2 of R11, and leg 2 of C8, they are all directly connected via traces with nothing in between/around them. Is it possible when you did this https://forum.pedalpcb.com/threads/butt-head-pedal-not-working-correctly.28405/page-3#post-369790 you lifted a pad or broke the trace on leg 2 of R10? I would check continuity between the same spot you are touching on R10 for tone with the #2 legs of C7, R11, C8. If continuous, then I am very confused, if not continuous, you could try tacking a piece of jumper wire onto the blob of leg 2 of R10 to any of those other 3 spots I keep mentioning.

View attachment 112002
I am hung up on what you are seeing between R10 and C8 and don't want to move farther down the audio path until I feel like the input/output at C8 are good and match what you hear on leg 2 of R10.

This is really helpful! It might be a day or two at this point before I can get back to the workbench, but I'll start by working through your suggestions here and post some results soon.

 

[xconverge]

This is my favorite thread currently, so take your time, I am just glad you are sticking with it.You have clearly already learned a few skills, no matter what happens. The PCB looks clean, the end result will hopefully be a working pedal, but learning more about what is happening in the schematic, learning more about using a DMM, the audio probe, what can and will go wrong, etc, I love it, its the only reason I do this hobby really. I am terrible at guitar and continue to find things to do adjacent to the hobby other than practice (and I certainly don't think I am alone on this board with this mentality)...

 

[Feral Feline]

...

With everything replaced and resoldered, I got the exact same behavior I noted originally with C8 and IC1. So, with nothing else obvious going on there, I went ahead and traced the tone through the rest of the audio path with my audio probe. From leg 1 of IC1 forward, I didn't find any components with notable tone absence or change at any point, so the only points in the whole audio path with behavior that seems incorrect to me are C8 and IC1.

I'm with xconverge, you've got to find out what's going on with C8. As xconverge pointed out, you should have SOUND on all common points connecting R10, C7, R11, and C8 — this is what's known as a "node". If I recall, you've got audio on both sides of R10 so how can you NOT have it on the node-connected side of C8?

If C8 is broken or the trace around it damaged or a short of the signal to ground (unlikely), then like a dam there should only be a trickle of signal at best beyond C8 — yet you mention you've got "tone" further downstream in the signal path.

I even plugged the pedal back into my amp and played through it, and I got the same results that started the whole process: the LOUD and LOW knobs both increase volume, and when either is turned down all the way, there's no signal going to the amp. (This seems normal for the LOUD knob, but not for the LOW knob?) The HIGH knob doesn't appear to do anything regardless of position, and the GRUNGE knob increases the volume and low end somewhat when turned up, but doesn't introduce any distortion into the circuit.
...

The LOUD knob is a normal volume control, typically (but not always) volume dumps signal to ground via the pot's lug 1. So when the VOLUME/LOUD knob is all the way down you won't get any output, so that's normal. GRUNGE is acting as it should.

What's not normal is for the LOW to act like a volume knob. There could be a short, the pot could be faulty, even the PCB could be faulty from the factory — one in a million spark-plugs off the production line is a dud, I found that out the hard way.

Whether the HIGH and LOW controls are working as they should be... well, one thing at a time. What's going on with C8?

At this point, either something's going on that I'm not even aware I should be looking/testing for, or else something's wonky at C8/IC1 that's persistent even after replacing those components.

A tiny whisper of a solder-bridge is enough to undermine your circuit. Get out the magnifying glass, keep looking, keep inspecting.
Oh, and when you refer to something, such as "IC1", please be specific — re IC1, be clear whether you're referring to the IC itself in general, or one of its two op-amps:

First IC1 op-amp in the schematic "IC1.1" (pins 1,2,3), and​

Second IC1 op-amp in the schematic "IC1.2" (pins 5,6,7).​

Being specific will help avoid confusion while communicating with fellow trouble-shooters.


As JimiLee noted, you should obtain voltage-readings from each of IC1's legs and post them.

1) should I be getting tone from both legs of C8?

YES, if by "tone" you mean a signal (be that from a guitar, Music-player, signal-generator, looper-pedal, etc).

2) should the tone going out of leg 1 of IC1 be louder than the tone coming out of leg 1 of IC2?

NO.
IC2.1 op-amp has a 220k resistor in its feedback loop, the IC1.1 op-amp has a max resistance value of 110k in its feedback loop.
So IC2.1 should be louder at its pin 1 than IC1.1's pin 1, if I read and understood the schematic correctly.
If either resistance was shorted, it would effectively turn that op-amp into a buffer.

I don't have a clear idea of where to go from here or what else to check, but (at the risk of sounding like a broken record), I'm open to suggestions! Could there be something going on with the pots? Or something non-PCB related? Is there some really basic thing that, as something of a noob, I might be overlooking entirely?

As a fellow noob, I'll say "Yes", there's something we could all be overlooking; there could be something going on with the pots, but nothing that the LOW pot would affect what's going on at C8.

Sorry for the short novel--just wondering if I've reach the end of the troubleshooting road. Thanks again for all the continued suggestions and support!

You only reach the end of the road when you find out what's wrong and then fix it.

Bad pot, replace it.​

Dud PCB (rare, but happens), replace it.​

Solder-bridge, heat it up and wick it away.​

Cold solder-joint, reheat-reflow and add solder if needed.​

etc​

You can, however, abandon this road and choose to build something else, revisit this path once you've got more experience/knowledge.


I think you're doing great. You're pro-active, trying to find solutions such as test/swapping new components on your oddy-knocky and not waiting to be spoon-fed a solution. You're already so much further along than I was when I started; actually, you're further along than I am right now. I'm horrible at troubleshooting my own builds — total deer-in-headlights. I've got a rather large collection of things to troubleshoot at the moment 'cause I tend to get frustrated and just move on and start a new project instead of dealing with the nitty-gritty problems.

So, keep at it, you'll get there.