The dreaded Boneyard howl :(

[midwayfair]

I've gots it.

Here's the thing, though: It's in a two-in-one with a Fatpants, and even with the fatpants in line first, the howl is just as bad -- making me speculate that an input buffer isn't going to help.

I'm seeing lots of suggested fixes for it, but almost nothing that actually pinpoints the CAUSE of the problem And all the suggestions to add a buffer to the circuit ... Why? The first op amp stage IS a buffer and nothing else. Is the oscillation somehow inherent in using the same IC for the input section as for the gain section? Is it a power filtering issue (it looks like there might not be enough in this circuit)? Is it maybe the ceramic caps being piezo microphonic?

[alanp]

If you're running it with a Fatpants, which also uses a charge pump, then what happens if you strip the Boneyard chargepump, and just run the board off the Fatpants (so it does both boards.)

[midwayfair]

If you're running it with a Fatpants, which also uses a charge pump, then what happens if you strip the Boneyard chargepump, and just run the board off the Fatpants (so it does both boards.)

The fatpants is actually piggybacking off the charge pump from the Boneyard in this. It let me make my layout smaller. I just made a tiny daughter board for the two diodes and 47uF and stuck them right under the charge pump, then ran the 18V out along the bottom of the enclosure over to the Fatpants.

[pryde]

I have built a few boneyards for self and others in both single and dual-channel versions. I always run an in-line klon buffer before it with great results.

I never had a problem with the squeal using a buffer (even high gain cranked full) until recently doing a build which surprised me. It was caused by the input wire (jack to 3PDT) placement. I moved the wire 1/2" over and all was quiet as a mouse  With this circuit, wire routing (or pcb trace) is a critical component as I learned.

Maybe try different wire routing, If no luck, then try a grounded input wire and see if that cures it.   

[midwayfair]

The things I've done to this ...

I tried shielded wire and repositioning. It doesn't make a difference until even unshielded input or output wire gets within maybe a millimeter of the output or input, respectively. Everything on the switches is as separate as possible.

I put a JFET buffer in front. This doesn't seem to help (also tried a couple other devices). Which is really what I expected ... the input of the circuit is a buffer. I don't see what a buffer can be doing in this circuit.

I added an extra low pass to the front of the circuit (1nF). Not much difference. The oscillation is way too low in the audio spectrum for filtering to kill it completely.

I've filtered the crap out of the power section, adding another 100uF, a 220nF film cap, and a 100R and schottky in series. This DID make a small difference, but not much.

I tried a few different FET-input chips. No difference.

One thing that did help a little is that I moved the volume pot to the end of the circuit (jumpering the original pads 2 and 3), and limiting its range with a 4k7 in place of the 100R (and removing the 1K). However, this really just means that "7" on the volume pot is like "4," so the howling still occurs at the same spot. It's still clearly positive feedback, and it's way down in the audio range, I'd say somewhere around 2KHz, so filtering it completely is out of the question.

I've never encountered anything like this. The Britannia oscillated, and I've had a fuzz or two that oscillated a little, but those were REALLY high frequencies that were pretty easily filtered out where they occurred. I can't even figure out what's causing the feedback in this pedal. It's positive feedback, but it has to be sneaking in on the PCB itself, because there's nothing left to do on the inputs and outputs. It doesn't even seem tied to the gain exactly, because the crunch pot oscillates just as quickly as the high gain pot.

Before I give up on this, does anyone have any ideas that I HAVEN'T tried? Or at least a good explanation for what the heck is causing this?

[jalmonsalmon]

Man yeah, I would love to know as well...
I made one of these and it does the howl, only way I got rid of it was to run an overdrive pedal in front with a buffer...
I tried putting a buffer inside on a daughter board but the howl came back   I have not tried to make a klon buffer but, would rather just solve the issue without a buffer as well...

[Willybomb]

I'm about to start on my own boneyard adventure.  I've got a klon buffer built up to put in, but I'm wondering if the howl isn't related to the TC1044/Max1044.  I've gotten mine from Tayda, but I'm building an OD820 as well which needs the same sort of thing, but I'd already placed the Tayda order and they're pretty rare locally.  I can get one from diyguitarpedals.com.au but I don't need anything else in the meantime to make up the order, lol.

I've read that you need the TC1044 with the -s appendage as they have some sort of clock noise moved up into the higher spectrum. .. could this be the issue people are having?