Butt Head Pedal Not Working Correctly

greypilgrim76

greypilgrim76

Member
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:

IMG_8465.jpeg IMG_8466.jpeg
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!
 
Last edited:
Sort by date Sort by votes
mybud said:
The audio probe connects to your amplifier. Try a site search here to find examples. It’s very simple to build.

With any audible signal as input, you use it to track back to where the audio stops. In that vicinity lies the problem. Then inspect the board to find the exact problem, whether a cold solder joint, too much or not enough solder and so on.
Click to expand...
Thanks for the info! So, just to double-check, I can feed a random tone generator signal from my phone into the pedal for testing with the audio probe?
 
Upvote 0 Downvote
greypilgrim76 said:
Thanks for the info! So, just to double-check, I can feed a random tone generator signal from my phone into the pedal for testing with the audio probe?
Click to expand...
Depending what I’m trying to troubleshoot, I’ve often just played music from my phone. Works fine for finding where the signal dies and a lot less annoying to listen to than a beeeeeeeeeeeep from a tone generator.

If it’s something where you really need to hear what the pedal is doing to a guitar signal, a looper is handy if you’ve got one.
 
Upvote 0 Downvote
Erik S said:
Depending what I’m trying to troubleshoot, I’ve often just played music from my phone. Works fine for finding where the signal dies and a lot less annoying to listen to than a beeeeeeeeeeeep from a tone generator.
Click to expand...

Plug for the MasFX DIY tower thingie (https://mas-effects.com/tower/), if you're building a lot of pedals this thing is awesome.
It has an add-on for a signal generator which has a dozen or so short guitar and bass loops in different styles, plus the plain beeeeeeep
tones, and an add-on for a speaker to keep things really self-contained on your bench. And it has a built-in audio probe pin.
 
Upvote 0 Downvote
To fully spell it out as well, here is how I would approach it...

I would plug my guitar into my cheap looper, record a basic loop, then move the looper pedal to IN FRONT of this pedal, then I would start the looper. I would then enable the effect and probe starting from the left and work to the right, using these points to check due to ease of finding them. Once you find where something weird is happening you can then start to poke around that specific area. Starting at the IN is a good way to prove the probe is working and I am happy with the volume level of my amp the probe is plugged into (should just sound like clean guitar or whatever sound with the effect "bypassed")

1771380831363.png
 
Upvote 0 Downvote
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.

BUTT HEAD schematic & main audio path.png

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.
 
Upvote 0 Downvote
greypilgrim76 said:
Both posts are helpful! Honestly, I have no idea how people figured this stuff out before internet forums existed. At least not in any timely fashion!
Click to expand...



For more than a thousand generations of DIY-Padawans,
the JEDIY-Mentors gave guidance, of circuit-knowledge and electronics-wisdom,
within the Old Mentorships.

OBI & LUKE solder-tuter.jpeg

Before the Dark Times, before the Internet-Experts.
 
Upvote 0 Downvote
How people figured it out pre-Web? Trial and (in my case, mainly) error.

The breadboard is your friend here, especially with finicky frustrating Fuzz Faces (just for you, Feral 😎) and other so-called beginner circuits which tripped me up big-time in my early days. Nowadays I breadboard stuff more often than not beforehand to test tweaks and so forth.

What’s my point, you ask?

Big fun when a) things work but bigger when you b) more or less understand why and how they do the marvellous things they do.
 
Upvote 0 Downvote
You must log in or register to reply here.
Back
Top