Big Muff Problem

[Diodo]

Hello, i built a Big Muff Pi months with the GGG PCB ago, and it had a problem, when i turn the TONE pot to a High treble, the BMP had a trebly beep when i wasn´t playing the guitar (when i was playing it, the sound was under).
I thought it was a problem of poor wiring or the cheap pots.

Well, two days ago, I rewired all, with new wire (the other was from a broken video), new Alpha pots, a Duty DPDT, millenium bypass 2, new jacks...
When I plugged it, it sounded like a high gain TS, very well, but with a few gain. I try to find the problem, it was a stupidity   , i have the 2N5089 in wrong side   , i putted them in the correct side and.. the Big Muff returned!!!
But it was back with a little, rare and disgusting problem, when i turned the GAIN pot, up to 75%, the BMP emited a treble, hight and disgusting beep, and this wasn´t overshadowed with the guitar sond.

And well, i have the BMP with the millenium and all, ready for putting it in a hard box, but first i need to resolve that problem, i was searching the problem with the probe, but i cannot exactly find it, i figured it was from the lug 3 of the GAIN pot, but is hard to find were the beep begins, is a low beep that is amplified with the BMP.

Any of you have had a similar problem?

Thanks, and excuse my bad english.

[lightningfingers]

The sound you're describing sounds like a similar problem that I had, it turned out I had put a wrong resistor on the emitter of Q4, so you might want to check that.

Also, well this is a super high gain pedal, the sound might just be microphonic feedback, which would occur if you turned the gain up high (I know mine does :wink: ) just a thought.......
what guitar do you use?

[Diodo]

Thanks for answering!
I use an Schecter C1+, is not microphony, is a more artificial Beep.

The only mod that it haves, is a higher resistor in the Base of the Q4 (like J.D. Sleep said, to increase gain) before, i only have nasty sounds when I put the Tone to high treble, or to extreme bass (it was a sporadic problem, as i said, i thought that was a problem of wiring)

This nasty sound comes when i put the Volume and the Sustain to very high values, and it dissapears when i reduce one of them. It's like... a pressure cooker.

It's crazy...

[vdm]

This sounds similar to a problem i had with the ROG 3 legged dog.
Try touching some metal parts in the circuit like the switch and the pots, and if this stops the piercing noise at all, it's probably a grounding problem. The solution was to use grounded input switch wiring from GGG.
Hope this helps,
Trent

[Eric H]

This nasty sound comes when i put the Volume and the Sustain to very high values, and it dissapears when i reduce one of them. It's like... a pressure cooker.

It's crazy...

Your circuit is oscillating. There are several suggestions for this in the effects FAQ. Keep input and output wires short, and separated from each other. Using shielded wire on the input frequently works (ground one end of the shield to the circuit-board --leave the other end ungrounded.
Finally, a tpdt switch can give you more space between the input/output wires at the switch.
" The solution was to use grounded input switch wiring from GGG. " VDM's suggestion will cure the problem if it oscillates in bypass --but you need a tpdt for this --doesn't work for millenium/dpdt circuits.Try the shielded input.

-Eric

[Diodo]

Thanks, I will try to find shielded wire in the electronic shop.

Well, the big muff doesn´t oscillate when is bypassed, it only does it when is ON.

Thanks!

[RDV]

The only mod that it haves, is a higher resistor in the Base of the Q4 (like J.D. Sleep said, to increase gain) before, i only have nasty sounds when I put the Tone to high treble, or to extreme bass (it was a sporadic problem, as i said, i thought that was a problem of wiring)

You might want to undo that mod as an easy fix along with the other suggestions.

RDV