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!

 

[xconverge]

Excellent update! There is a lot there but I will state a few things that come to mind

1. Continuity mode on a meter/beeping is great, but looking at the number or setting the meter to ohms/resistance is even "better". Continuity on most meters is a glorified "resistance is <= X, beep" I think. So components can come into play and some meters can beep/flickerbeep at certain points. For some tricky areas, using resistance and looking for 0 ohms or a short is even better for "is this literally a wire connection at a node" or just something that is a bit more intermittent.

2. MAYBE the audio signal (AC) was going through R11 to the VREF line as the path of least resistance (due to the infinite resistance/no connection at C8) and then back into the audio pipeline via VREF at R27, just spit balling here though...someone else feel free to tell me why this isn't possible. It is weird to think about, but AC and DC can and does exist on the same wire at the same time.

3. Assuming your jumper is on the right legs and not 10 feet long, it should not change anything about noise/squeal. If it were on the wrong leg of C8, then C8 wouldn't be doing it's job in the circuit and that wouldn't be good.

4. The real treasure was the friends we made along the way with this pedal it seems based on the above posts/resulting sounds you get out of it, congratulations on learning a lot and thanks for sticking with it, I enjoyed helping out thoroughly.

 

[greypilgrim76]

Excellent update! There is a lot there but I will state a few things that come to mind

1. Continuity mode on a meter/beeping is great, but looking at the number or setting the meter to ohms/resistance is even "better". Continuity on most meters is a glorified "resistance is <= X, beep" I think. So components can come into play and some meters can beep/flickerbeep at certain points. For some tricky areas, using resistance and looking for 0 ohms or a short is even better for "is this literally a wire connection at a node" or just something that is a bit more intermittent.

This is helpful. I haven't had much reason to sort through the nuance of continuity checking beyond "beep" or "no beep."

2. MAYBE the audio signal (AC) was going through R11 to the VREF line as the path of least resistance (due to the infinite resistance/no connection at C8) and then back into the audio pipeline via VREF at R27, just spit balling here though...someone else feel free to tell me why this isn't possible. It is weird to think about, but AC and DC can and does exist on the same wire at the same time.

Yeah, I honestly have no idea what the underlying issue was or why the jumper wire fixed it. Given my reflowing and swapping of a few components, I'd like to think it wasn't operator error, but who knows? My best guess is maybe the connection in the PCB itself either was faulty or became faulty through something I did. I soldered the jumper wire to the backside of the PCB (the side without components), so the signal was at least getting through to that surface. To quote Yul Brynner, "Is a puzzlement!"

3. Assuming your jumper is on the right legs and not 10 feet long, it should not change anything about noise/squeal. If it were on the wrong leg of C8, then C8 wouldn't be doing it's job in the circuit and that wouldn't be good.

Also good to have this confirmation!

4. The real treasure was the friends we made along the way with this pedal it seems based on the above posts/resulting sounds you get out of it, congratulations on learning a lot and thanks for sticking with it, I enjoyed helping out thoroughly.

Yep, this was way more fun than I expected it to be, even if it was also frustrating, time consuming, and a little maddening! Glad I didn't chuck the whole thing in the bin a month ago!

 

[Feral Feline]

Awesome! Way to persevere!
I will take a page from your notebook, and get back to tackling some of my trouble-shooting backlog.


I'm thinking maybe the PCB you got was one of those 1-in-a-million with a fault — maybe no trace or damaged trace during manufacturing at the R10–C8 node.

Great colour, love the purple lettering. Maybe order some purple knobs with your next round of parts?


WHAT'S NEXT!?


[I wrote the above yesterday, didn't hit "Post reply" — and yet I still wonder how mistakes creep into my builds ]

 

[greypilgrim76]

WHAT'S NEXT!?

I actually just placed my next PCB order:


I decided to knock out the remaining JHS clones I didn't have and then start down a few new and interesting paths. I'm particularly excited about the Cepheid Chorus and the Parentheses Fuzz! (I also can never get enough of the Big Muff variants.)