SOLVED 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.

 

[greypilgrim76]

So I'm probably still a day or two away from finding some workbench time to get answers to the specific troubleshooting suggestions and questions some of you have offered, but I've got a lull at work at the moment, so I wanted to respond to a few questions/comments that don't require me to have the hood open on the pedal:

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.

I'm using a square wave tone generator on my phone from a website. While the relative volume level changes depending on where I'm testing, anywhere that I say I've "got tone," that's the tone I'm getting, and it sounds like the same type of tone in each location. Would it be helpful to play something musical through the circuit to ensure it's the same signal at all points?

I'm glad to have confirmation that I should be getting the exact same signal in the node between R10, C7, R11, and C8. Part of my problem is that I don't always know how I should expect discrete components to behave when tested in various ways, so I wasn't sure whether C8 having no tone was expected or a problem. Knowing it's a problem definitely helps me zero in on troubleshooting approaches.

A couple of additional questions about this node: first, I can't tell from the schematic and PCB which leg of R10 is leg 2--would it be the one closer or further from the left edge of the PCB?

Second, if I can't get tone on leg 2 of C8 even after reflowing, would it be advisable to run a jumper wire from leg 2 of R10 to leg 2 of C8 to see if that gets me tone, or would jumping "over" C7 and R11 with the wire cause problems?

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)...

It's funny--when the pedal didn't work at first, I was super annoyed and kind of wanted to just order a new PCB and start over. The troubleshooting process felt more challenging and less "fun" than the build process. Even when I started basic troubleshooting, I was sure that if it wasn't an easy fix, I'd just ditch it. I certainly had no intention of building an audio probe and taking this deep of a dive when it was first suggested. But after each failed troubleshooting session, I'd think "But maybe I can just check this one other thing..." and before I knew it, I had an audio probe built and was working through the signal path.

At this point, I think the troubleshooting has become its own version of "fun," or at least rewarding in a different way than the building. Even just looking back through this thread, it's amazing what me from a couple of weeks ago didn't understand at all that now makes perfect sense to me, even if there's still a crap-ton of stuff I remain clueless about!

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.

This is the central puzzle for me at the moment. There's no good reason to have tone on the downstream side of R10 and not on C8 that I can see. The soldering looks good and I didn't see a lifted pad when I temporarily swapped R10 with R6. And yeah the fact that the tone reappears on leg 1 of IC1.1 after being absent on both legs of C8 seems weird, especially since it's also not present on legs 2 or 3 of IC1.1.

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?

It's actually really helpful to know that GRUNGE seems to be doing its job correctly, because I sort of assumed it wasn't. If I can figure out the R10/C8 node issues, I'm guessing that the LOW and HIGH pots might be my next investigation...

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.

Useful advice! Thanks! Up to this point, I think every reference I've made to "IC1" is really "IC1.1" because I haven't really made it to the "IC1.2" part of the schematic beyond my quick trace of the tone through the circuit.

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.

Another useful bit of info! I just assumed that each stage of the circuit would make the signal louder, which probably shows the limits of my understanding on what some of the components actually do from a technical POV.

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.

Thanks! Like I said, I didn't expect to get this far into the weeds, but I honestly don't hate it here, even if the weeds are pretty tall and I can't really see over them.

 

[jimilee]

Learning to troubleshoot will help immensely. It will speed up the process and help you l ow where to start, on future builds. I find it gratifying as well.

 

[pbrommer]

Seconded with jimilee -- forcing yourself to find the problem makes solving other stupid problems that will show up in the future easier.

Don't ask me how I know: I keep making stupid errors.

 

[xconverge]

I'm using a square wave tone generator on my phone from a website. While the relative volume level changes depending on where I'm testing, anywhere that I say I've "got tone," that's the tone I'm getting, and it sounds like the same type of tone in each location. Would it be helpful to play something musical through the circuit to ensure it's the same signal at all points?

I would use a sine wave instead of a square wave. Even more preferable for me would be to use a looper with some clean guitar going into it. Start with using a sine wave instead of a square wave if you don't have a looper laying around.

first, I can't tell from the schematic and PCB which leg of R10 is leg 2--would it be the one closer or further from the left edge of the PCB?

I don't know, this is where I would use continuity on my DMM. One side (the left side in the schematic) of R10 is directly (through traces) connected to IC2.1 pin 1. So put one DMM probe on pin 1 of IC2.1, and then the other probe on one side of R10. If it beeps then that is the left side of R10 on the schematic. If it doesnt, try the other side of R10 on the board. The reason I am suggesting finding that side (leg 1) of R10 is because leg 2 is the suspect one to me. You can and should then repeat the test once you know for sure which one is leg 2 (because you just found which one was leg 1). Leg 2 of R10, you can then put one probe of the meter on, and with the other probe, touch both sides of C8, both sides of C7, both sides of R11, etc to find which side of each are all in this screenshot of the single node (center point of the diagram here).

Second, if I can't get tone on leg 2 of C8 even after reflowing, would it be advisable to run a jumper wire from leg 2 of R10 to leg 2 of C8 to see if that gets me tone, or would jumping "over" C7 and R11 with the wire cause problems?

From the same diagram above... Picture the audio signal through the schematic/pedal as a meandering river. at various points in the river there are blocks/beaver dams/whatever that each alter the water in certain ways, these could be ICS, capacitors, resistors, whatever.

In the diagram above, the river flows directly from R10 leg 2 to C8 leg 2 with nothing in between. There are 2 little off-shoots of the river (streams?) that go to leg 2 of C7 and leg 2 of R11 (and then through other "things", the actual capacitor/resistor/etc).

What this means, is that in between R10 leg 2, C7 leg 2, R11 leg 2, C8 leg 2, it is all the same water with nothing in between around them.

If you oriented the components correctly, you could even just solder all of those legs together in a big blob (this is essentially the core of how "point to point" wired pedals work. The traces on the board do this already for you. SO, according to the schematic, all 4 of those leads should ALREADY be touching eachother or have continuity with the DMM.

The chances of leg 2 of R10 or the pad being broken/damaged, leg 2 of c7 also being damaged, leg 2 of r11, being damaged and/or leg 2 of c8 all or at least more than 1 being damaged is less-likely to me than just 1 of those being damaged. If you really wanted to, you could solder multiple jumper wires on, to "recreate" the traces in the board, but I think if you just solder a single jumper wire, it will reconnect the single damaged pad back with the other 3 components at the node. (As long as you are connecting it to the right leg according to the schematic, the ones that are all part of the same node/junction)

 

[DDad]

Here's the schematic with the main audio-path outlined in green, and of course you'll find audio elsewhere, such as in the pink boxes and any bits connected to them, op-amp IC3.1 for example will have audio on it.

View attachment 111565

So using your audio-probe, follow the signal from the IN along the path and if you got to, say for example C11 and it sounds horrible, but it sounded okay just before that at C8, then you'd start exploring the components around IC1.1: C9, R12, R13, C10 and the GRUNGE pot...
Check them with the audio-probe;
inspect their solder-joints and reflow;
look for damage to the components that may have been missed when populating them;
look for gossamer-strands of solder causing shorts...

[EDIT]
DOH! xconverge beat me to it.

In the 1st and 3rd op amps the pink I understand (gain determining resistor and high frequency cap), but what is the section below those doing that have the transistor? How does that affect the gain? Or affect other than gain?

 

[Feral Feline]

In the 1st and 3rd op amps the pink I understand (gain determining resistor and high frequency cap), but what is the section below those doing that have the transistor? How does that affect the gain? Or affect other than gain?

I believe they're gyrators, which I don't know much about, that help shape the overall tone.

Reading this,

Simple, Easy Parametric and Graphic EQ's, Plus Peaks and Notches

might answer some questions.

May be some interesting titbits here:

https://www.freestompboxes.org/viewtopic.php?t=13948

Watch this video about gyrators. Lots of other vids out there on gyrators/EQ.

If all that still leaves you with further queries...

Best start your own thread and solicit info in General Questions.





Back to C8...

 

[greypilgrim76]

Okay, so it took a bit longer than I expected to get back to the work bench, but I've got some good news and some additional questions. First, though, here are a few answers I promised (in case anyone finds this thread down the road and wants to follow the bread crumbs):

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

IC1 voltages are as follows:

Pin 1: 4.5v​

Pin 2: 4.5v​

Pin 3: 4.5v​

Pin 4: 0​

Pin 5: 4.5v​

Pin 6: 4.5v​

Pin 7: 4.5v​

Pin 8: 9v​

​

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 switched my tone from a square wave to a clean electric guitar loop I found online. Running this sound through the board confirmed that I was getting sound until I got to C8 and then it didn't turn up again until leg 1 of IC1.1. I cranked the amp just to make sure I wasn't missing anything faint on the points between leg 2 of R10 and leg 1 of IC1.1, but there was no guitar sound until it popped back up on leg of IC1.1. I still don't really understand how the tone can disappear and reappear like that, but I guess there's probably a reason somewhere in an electronics textbook...

A tiny whisper of a solder-bridge is enough to undermine your circuit. Get out the magnifying glass, keep looking, keep inspecting.

Triple checked everything with the magnifying glass, and everything looked copacetic as far as I could tell.

I would use a sine wave instead of a square wave. Even more preferable for me would be to use a looper with some clean guitar going into it. Start with using a sine wave instead of a square wave if you don't have a looper laying around.

Yep, switching the actual guitar tone helped--thanks for that tip!

I don't know, this is where I would use continuity on my DMM. One side (the left side in the schematic) of R10 is directly (through traces) connected to IC2.1 pin 1. So put one DMM probe on pin 1 of IC2.1, and then the other probe on one side of R10. If it beeps then that is the left side of R10 on the schematic. If it doesnt, try the other side of R10 on the board. The reason I am suggesting finding that side (leg 1) of R10 is because leg 2 is the suspect one to me. You can and should then repeat the test once you know for sure which one is leg 2 (because you just found which one was leg 1). Leg 2 of R10, you can then put one probe of the meter on, and with the other probe, touch both sides of C8, both sides of C7, both sides of R11, etc to find which side of each are all in this screenshot of the single node (center point of the diagram here).

View attachment 112208



From the same diagram above... Picture the audio signal through the schematic/pedal as a meandering river. at various points in the river there are blocks/beaver dams/whatever that each alter the water in certain ways, these could be ICS, capacitors, resistors, whatever.

In the diagram above, the river flows directly from R10 leg 2 to C8 leg 2 with nothing in between. There are 2 little off-shoots of the river (streams?) that go to leg 2 of C7 and leg 2 of R11 (and then through other "things", the actual capacitor/resistor/etc).

What this means, is that in between R10 leg 2, C7 leg 2, R11 leg 2, C8 leg 2, it is all the same water with nothing in between around them.

If you oriented the components correctly, you could even just solder all of those legs together in a big blob (this is essentially the core of how "point to point" wired pedals work. The traces on the board do this already for you. SO, according to the schematic, all 4 of those leads should ALREADY be touching eachother or have continuity with the DMM.

The chances of leg 2 of R10 or the pad being broken/damaged, leg 2 of c7 also being damaged, leg 2 of r11, being damaged and/or leg 2 of c8 all or at least more than 1 being damaged is less-likely to me than just 1 of those being damaged. If you really wanted to, you could solder multiple jumper wires on, to "recreate" the traces in the board, but I think if you just solder a single jumper wire, it will reconnect the single damaged pad back with the other 3 components at the node. (As long as you are connecting it to the right leg according to the schematic, the ones that are all part of the same node/junction)

Okay, so this was the workflow I spent most of my time today working through, testing continuity and trying to sort which legs were which on the relevant components. I started by checking continuity between IC2.1 leg 1 and R10. I found that the right side of R10 (looking down at the side of the PCB with visible components) had full continuity. There was none between IC2.1 leg 1 and the other leg of R10, so I assumed that the right side of R10 is leg 1 and the left side is leg 2.

Here's where it gets interesting. When I checked continuity between R10 and C7, R1, and C8, I got the following results:

-No continuity between leg 2 of R10 and any of the other components​

-A three-second(ish) continuity tone between leg 1 of R10 and leg 2 (I assume) of C7​

-A short beep of continuity tone between leg 1 of R10 and leg 2 (I assume) of R11​

-No continuity between leg 1 of R10 and either leg of C8​

A lot of these results didn't make clear sense to me. I didn't understand why I was getting continuity to later components from leg 1 of R10 but not leg 2, and I also wasn't sure if the differences in tone length meant anything or were just symptoms of component types and their location in the schematic. Regardless, though, this all made me think that, whatever else was going on, the complete lack of continuity between R10 and C8 was the most obvious weirdness.

So, I just decided to take a shot and solder a jumper wire between leg 2 of R10 and what seemed to be leg 2 of C8. As soon as I did that, I got wildly different results from both my continuity checks and the sound probe. There was clear continuity between all legs in the R10/C7/R11/C8 node, and when I checked the guitar loop tone at IC1.1, it was much louder and had a distorted sound. I figured, okay, maybe we're onto something, and reassembled the pedal to check it with my actual amp and guitar.

The difference is night and day. The knobs all appear to be working correctly. I'm getting pure volume increase/decrease (down to no sound at all) from the LOUD knob, and both LOW and HIGH do exactly what they should. When the GRUNGE knob is turned down all the way, the pedal is still fairly heavily distorted, and as I turn GRUNGE all the way up, the sound goes from distortion to something more fuzz-like all the way to whatever's past fuzz.

Basically, I think my jump from R10 to C8 solved the problem, and I can't thank everyone enough for all the guidance to help get this sorted. My only remaining questions/concerns are whether some remaining odd behavior is due to me misidentifying the legs on some of the components, or if this pedal is just quirky. Here's what still seems off (or at least unusual to me):

First, if I've got the pedal engaged and unplug the guitar cable from my guitar, I get a sustained squeal. Not the kind that you get just when you get the tip of the cable input close to the jack, but a nonstop tone regardless of where the cable tip is in relation to the guitar or anything else. Is this normal?

Second, the pedal is very noisy with the GRUNGE knob turned up. Like, it makes my RAT sound quiet in comparison. It sounds fine when I'm playing, but the minute I stop, the noise is considerable. Is this also normal for this pedal?

I guess the only variable I'm concerned about is whether I've correctly jumped R10 leg 2 to C8 leg 2, and if I haven't, would that make the pedal noisy/squealy, or is that just the special "character" of this pedal? (I've never played an actual DOD Grunge, but some internet searching makes me think this is just how the pedal is.)

So, basically, I think this is either resolved or very close to resolved. I'll wait to mark it as SOLVED until I have a better sense of what's going on with the noise. I honestly have no idea why there was no notable connection between R10 and C8 when all of the soldering was solid, but some mysteries aren't meant to be solved, I guess!

Thanks again for all the help, and let me know if you've got thoughts on these last couple of questions!

 

[greypilgrim76]

PS--While I'm still interested in hearing any thoughts about the noisiness, my own research suggests this pedal is functioning as expected. The weird squeal went away once I fully assembled everything, and the noise, while still considerable, seems a bit more manageable now with some careful tweaking of the GRUNGE knob. It's still hella noisy, but I'm skeptical there's anything actually wrong here. So, I'll mark this thread as SOLVED.

Thanks one last time to everyone for the help. There would be zero chance of this ending well without all of your suggestions, and I feel like I got a pretty decent troubleshooting master class from you, too.

Originally, I was going to call this thing "Lithium Distortion," as a sort of nod to its grunge roots, but after the long, frustrating, and sometimes rage-inducing process of fixing it, I settled on a new name:

 

[jimilee]

Congratulations!!! I just hate you spent so much time on that particular pedal. I have an original and I built one. Couldn’t make myself like either one of them. Maybe you can make it sound better:

 

[greypilgrim76]

Congratulations!!! I just hate you spent so much time on that particular pedal. I have an original and I built one. Couldn’t make myself like either one of them. Maybe you can make it sound better:

Ha! Yeah, it probably would've been slightly more rewarding to finally get my first Klon clone or something like that working, but honestly, one of the reasons I ordered the Butt Head was because I'd read so many articles and watched so many videos about what a bizarre pedal the original Grunge was. I gotta say, having finally gotten it working, all of my suspicions have been confirmed.

I feel like there might be a very narrow but definitely achievable window of not-terrible sound in there, although I'm honestly kind of flabbergasted by just how much actual auditory pain can be achieved by cranking the HIGH and turning the LOW all the way down. Total icepicks into my ears. (To be fair, I was using my Tele.) Overall, so far it's like watching Plan Nine from Outer Space or The Room--painful, but also kind of astonishing in its own right and worth witnessing. Once, at least.

 

[jimilee]

Ha! Yeah, it probably would've been slightly more rewarding to finally get my first Klon clone or something like that working, but honestly, one of the reasons I ordered the Butt Head was because I'd read so many articles and watched so many videos about what a bizarre pedal the original Grunge was. I gotta say, having finally gotten it working, all of my suspicions have been confirmed.

I feel like there might be a very narrow but definitely achievable window of not-terrible sound in there, although I'm honestly kind of flabbergasted by just how much actual auditory pain can be achieved by cranking the HIGH and turning the LOW all the way down. Total icepicks into my ears. (To be fair, I was using my Tele.) Overall, so far it's like watching Plan Nine from Outer Space or The Room--painful, but also kind of astonishing in its own right and worth witnessing. Once, at least.

Bwahahahahahaahahaha