"Power Pig", my Sabbath Distortion (Catlinbread Sabbra Cadabra)

[tablebeast]

Build Rating

5.00 star(s)

Build #3 of something like 12. Power Pig here is my clone of the Catlinbread Sabbra Cadabra, using the Sabbath Distortion PCB. SO, this thing sounds pretty awesome. I've only used it with at 9 volts and with a synth so far, so I don't know how it sounds with an SG+Humbuckers. Regardless, I'm really digging the tone. The build was easy and the documentation was complete. I got no complaints about the build.

I do have one problem that I need to troubleshoot. Turns out this is a little TOO much like an old Rangemaster + Supergroup Amp. Thats because I'm getting a constant self-oscillation tone with no signal applied. It reminds me of what high gain tube amps that need service do! My jacks are securely mounted with star washers to the case and I only have the ground wire for the input connected to the input jack, so I don't think its a grounding issue. This oscillation happens at all volumes, but it changes significantly depending on settings, cranking them up seems it make it go away.

 

[tablebeast]

Anyone else have problems with self oscillation? Its like this thing has tinnitus of it's own.

 

[jwin615]

Try moving the input wire further from the PCB.

 

[MattG]

My jacks are securely mounted with star washers to the case and I only have the ground wire for the input connected to the input jack, so I don't think its a grounding issue.

In the gutshot, it looks like the input output jack's sleeve (ground) isn't connected at all?

Does the problem go away if you put another known-good pedal between this pedal and your guitar?

Edit: fix typo.

 

[tablebeast]

In the gutshot, it looks like the input jack's sleeve (ground) isn't connected at all?

Does the problem go away if you put another known-good pedal between this pedal and your guitar?

The ring for the input on the left is unconnected. The ground on the output jack on the right is not connected to the ground point on the board, but thats because its connected to the metal chassis via a star washer on the jack. I originally did have that ground wire connected, but it made a ground loop, so I disconnected it. Both points still show a ground connection. I didn't hear a difference either way. I have not tried to put another pedal in front of it, but it makes the same oscillation with nothing plugged in at all, just a cable plugged in, a synth plugged in, or a guitar plugged in. The oscillation happens when there is nothing being played through it and as soon as I make some sound it overwhelms the oscillation and seems to go away, but I'm pretty sure its still there, quietly, under the loud sounds.

 

[tablebeast]

I'll record some samples and post a video soon.

 

[MattG]

The ring for the input on the left is unconnected. The ground on the output jack on the right is not connected to the ground point on the board, but thats because its connected to the metal chassis via a star washer on the jack. I originally did have that ground wire connected, but it made a ground loop, so I disconnected it. Both points still show a ground connection. I didn't hear a difference either way. I have not tried to put another pedal in front of it, but it makes the same oscillation with nothing plugged in at all, just a cable plugged in, a synth plugged in, or a guitar plugged in. The oscillation happens when there is nothing being played through it and as soon as I make some sound it overwhelms the oscillation and seems to go away, but I'm pretty sure its still there, quietly, under the loud sounds.

Ahh yes, output jack, I corrected my previous post. But your point remains, either way.

I agree with @jwin615, try moving that input wire away from the PCB. That goes for the long wire that runs from the jack down to the switch. But also: try to put some space between the wires that connect the PCB to the switch. Those are longer than they need to be, and any of those signal-carrying wires could be coupling to the input. I would just fire up your amp and pedal, get it oscillating, then move the wires around and see if that changes the oscillations at all. If so - it's a clue.

Shielded wire - particularly the long runs from the jacks to the switch - might help too.

 

[tablebeast]

Ahh yes, output jack, I corrected my previous post. But your point remains, either way.

I agree with @jwin615, try moving that input wire away from the PCB. That goes for the long wire that runs from the jack down to the switch. But also: try to put some space between the wires that connect the PCB to the switch. Those are longer than they need to be, and any of those signal-carrying wires could be coupling to the input. I would just fire up your amp and pedal, get it oscillating, then move the wires around and see if that changes the oscillations at all. If so - it's a clue.

Shielded wire - particularly the long runs from the jacks to the switch - might help too.

Aha, thats what I'll try the next time I troubleshoot it. I also just wondered if perhaps I had anything else around it like a cell phone or other electrically noisy bit of electronics. I figured I'd hit you guys up first and see if I had made any obvious or common mistakes and I think you just nailed the first place to check! Thanks.