Superfuzz issue - sharp volume swell after muting a note (now w/ voltages!)

[Nitefly182]

Im working on a superfuzz-based circuit (Prescription Depth Charge) and any time I have the gain above about half way the pedal with squeal for a second or two after I stop playing but then the squeal will stop. So it will sound great when I am playing, then Ill mute the string, and after a fraction of a second there will be a loud squeal. If I turn down my guitar volume after I mute the strings there is no squeal so it seems to be a short sharp rise in gain level after you mute the strings and this is very perplexing to me. Has anyone ever come across this kind of issue? Changing the wiring layout doesn't have any effect on the problem. Its also not a standard gain/feedback issue because the squeal stops after a moment and doesn't just continue.

[Kipper4]

Please share the diagram of what you are working too.

Then go to the debugging page and report back.
https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Help us to help you.

[Nitefly182]

This is the layout although it has some errors around the tone control that I corrected before building. I also removed the 47uf electro in parallel with the emitter resistor of Q3 (recovery stage at the end of the circuit) because it is not in the original depth charge circuit.


This is the schematic:


The circuit works in every way. The controls all work properly and it sounds great. It just has this issue where, if the gain is above about halfway, after you stop playing and mute the strings with your hands there is a sharp rise in gain/volume of the circuit that causes a blast of feedback. Its almost like there is a compressor working that is trying to raise the reduced input voltage up to the level if the distorted sound. I can see that being an issue with a fuzz circuit but other pedals that use a similar architecture don't have this problem. Here is a pile of voltages. These are listed according to the numbers in the schematic since its easier to see the architecture that way.

Supply voltage: 9.77 V

Q1
B .695 V
C 3.86 V
E 125.7 mV

Q2
B 3.84 V
C 9.77 V
E 3.24 V

Q3
B 3.02 V
C 7.29 V
E 2.46 V

Q4
B 1.74 V
C 2.25 V
E 1.14 V

Q5
B 1.72 V
C 2.25 V
E 1.14V

Q6
B 1.25 V
C 3.32 V
E .645 V

[PRR]

> Q4   C 1.28 V
> Q5   C 2.33 V

Q4 Q5 Collectors are tied together. How can they be different voltage?

[Nitefly182]

> Q4   C 1.28 V
> Q5   C 2.33 V

Q4 Q5 Collectors are tied together. How can they be different voltage?

Transcription error with these ECB pinouts. The correct voltages are in the post now. Sorry!

[aelling]

I have an original grey box/black paddle Univox Superfuzz that does a similar thing, for me it's more like an ocean of hiss and a gate effect clamping it down like a split second after muting the strings. I've build clones as well and seem to remember the same thing happening with those, so I think it's just the nature of this thing.

[Nitefly182]

I have an original grey box/black paddle Univox Superfuzz that does a similar thing, for me it's more like an ocean of hiss and a gate effect clamping it down like a split second after muting the strings. I've build clones as well and seem to remember the same thing happening with those, so I think it's just the nature of this thing.

It may also be my bass that is susceptible to this issue. Ill have to test with a guitar and see if it happens there.