SOLVED Squeeeeeal like a rat!

[SYLV9ST9R]

I’m finally getting to fixing this one.
Muroidea with bass « contour » pot added.
I got squealing when I put the Dirt knob over 1 o’clock. I can attenuate it with the Bass knob (or the Pro-filter it’s paired with), but it’s still annoying
From what I’ve read, I’ll start by re-routing the power wires going to the relay bypass, but I’ll take any pointers as I’ll unbox it and work on it tonight.

 

[fig]

I'll be lurking while you track down the dreaded swine wave. Hope it's an easy fix!

 

[mdc]

If you run a buffered pedal in front of it does the squealing disappear?
On some LM308N builds, increasing the 30p cap (C6 on the muroidea schematic) to 100p can fix that issue but I'm not sure if that would help with a different opamp.

 

[SYLV9ST9R]

If you run a buffered pedal in front of it does the squealing disappear?
On some LM308N builds, increasing the 30p cap (C6 on the muroidea schematic) to 100p can fix that issue but I'm not sure if that would help with a different opamp.

Thanks, will try it with a buffer in front. I’m using either a CA3130EZ or a TL071 (still undecided between the 2) so I’ll try other fixes but keep this one in mind

 

[SYLV9ST9R]

If you run a buffered pedal in front of it does the squealing disappear?

Buffer before does it. I’ll have to rework my signal chain but that would do it. I’ll still try to reroute the power cable that are parallel to the audio lines. Thanks again

 

[mdc]

I've got a few vintage rats where this has been an issue and a buffer almost always solves the problem. Unfortunately, I haven't been able to chase it down at the PCB level. My chunderheaded understanding (please someone with more technical understanding jump in here and save me from myself) is that it most likely has something to do with phase shifting in the higher frequencies as the gain increases combining with some capacitive coupling between the input and output creating a feedback loop.

How you would go chasing this down at the component level is far beyond my pay grade. I've replaced almost every capacitor in an old rat pedal and increased the 30pf to 100pf and still had the oscillation problem persist. And as your experience seems to show, swapping out the opamp isn't a surefire fix either.

 

[SYLV9ST9R]

I've got a few vintage rats where this has been an issue and a buffer almost always solves the problem. Unfortunately, I haven't been able to chase it down at the PCB level. My chunderheaded understanding (please someone with more technical understanding jump in here and save me from myself) is that it most likely has something to do with phase shifting in the higher frequencies as the gain increases combining with some capacitive coupling between the input and output creating a feedback loop.

How you would go chasing this down at the component level is far beyond my pay grade. I've replaced almost every capacitor in an old rat pedal and increased the 30pf to 100pf and still had the oscillation problem persist. And as your experience seems to show, swapping out the opamp isn't a surefire fix either.

This is also way beyond my comprehension. But you provided a fix, and it’s good enough for me! Thanks again, again!!

 

[SYLV9ST9R]

I had tried a buffered pedal before, but it only worked a couple of times and then the squealing was back.
Finally, a friend suggested that I put a Klon buffer in before the circuit, and that's what I did and that did the trick.
Not as satisfying as completing a new pedal, but I've been trying to fix all the "needing troubleshooting" pedals on my shelf, and so far, that's 2 in 2 weeks, so yeah!

 

[music6000]

I’m finally getting to fixing this one.
Muroidea with bass « contour » pot added.
I got squealing when I put the Dirt knob over 1 o’clock. I can attenuate it with the Bass knob (or the Pro-filter it’s paired with), but it’s still annoying
From what I’ve read, I’ll start by re-routing the power wires going to the relay bypass, but I’ll take any pointers as I’ll unbox it and work on it tonight.

View attachment 11610

Use Shielded INPUT Jack & OUTPUT Jack to PCB Wires!
Ground shielded wire to Jacks on One end only!
Run them on each side of enclosure, not overPCB & FOOTSWITCHES!

 

[SYLV9ST9R]

Use Shielded INPUT Jack & OUTPUT Jack to PCB Wires!
Ground shielded wire to Jacks on One end only!
Run them on each side of enclosure, not overPCB & FOOTSWITCHES!

I did exactly that (even ordered some RG174 wire just for this use), but the squeal was still there...
The buffer fixed it though.