sudden feedback like noise from overdrive pedal.

[nguitar12]

OK so I built a YATS overdrive pedal according to the following diagram



Everything work perfectly but after a while of play I find that it suddenly produce  feedback like high frequency noise when the gain knob turned all the way up. It produce a (sustained V...V.....) sound when the guitar is not been playing. I am pretty sure it is not a feedback since the noise still there when I am using a headphone.

Can someone please tell me what is going on? Thanks.

[WhiskeyMadeMeDoIt]

High gain amplifiers are just a small step from an oscillator. What you are hearing is self oscillation.

[nguitar12]

High gain amplifiers are just a small step from an oscillator. What you are hearing is self oscillation.

I find that the problem happen only when I install everything into the 1590a box, with 3pdt switch. What is causing that?

[WhiskeyMadeMeDoIt]

Wire routing is usually the culprit. Move stuff around and see if it dies down.

[nguitar12]

High gain amplifiers are just a small step from an oscillator. What you are hearing is self oscillation.

So how to resolve this problem?

[WhiskeyMadeMeDoIt]

Keep your input as far away as possible from your output. keep your wiring short as possible.

[GibsonGM]

If you can get the circuit into the box, you may be able to move some wires around with a pencil until the oscillation stops.   Like Whiskey said - keep them short, and you may also want to shield your input wire (use shielded wire, grounded at ONE end only).

This oscillation occurs when you box the circuit because of something called STRAY CAPACITANCES, or "Inter-element capacitances".  Also, "Self-induction", sometimes  (just things for you to look up and read about).   

This causes signals to "couple" into places that they should not.    You may have the output of the chip coupling into the input wire, for example.  This will create a path for feedback like you describe.    Our job is to limit the amount of coupling that is possible.   The coupling occurs, simply, because you have a fluctuating AC signal that has been amplified, which induces a current in nearby wiring which then re-amplifies the signal in a feedback loop.   Just like bringing your guitar near the amplifier when it is turned up loud and you're not playing.

Routing wires properly, good layout, using shielded wire, and a good ground plan ("star grounding") all can help. There are also methods to de-couple troublesome circuits, but most you'll find on here are already 'good to go'.    Sometimes, though, your circuit is so high-gain that you just have to play over the noise     You turn it on as you start playing...

If you experience oscillation in a pedal at LOW volumes, though, you should be able to do some of the above to limit the oscillation.

[nguitar12]

If you can get the circuit into the box, you may be able to move some wires around with a pencil until the oscillation stops.   Like Whiskey said - keep them short, and you may also want to shield your input wire (use shielded wire, grounded at ONE end only).

This oscillation occurs when you box the circuit because of something called STRAY CAPACITANCES, or "Inter-element capacitances".  Also, "Self-induction", sometimes  (just things for you to look up and read about).   

This causes signals to "couple" into places that they should not.    You may have the output of the chip coupling into the input wire, for example.  This will create a path for feedback like you describe.    Our job is to limit the amount of coupling that is possible.   The coupling occurs, simply, because you have a fluctuating AC signal that has been amplified, which induces a current in nearby wiring which then re-amplifies the signal in a feedback loop.   Just like bringing your guitar near the amplifier when it is turned up loud and you're not playing.

Routing wires properly, good layout, using shielded wire, and a good ground plan ("star grounding") all can help. There are also methods to de-couple troublesome circuits, but most you'll find on here are already 'good to go'.    Sometimes, though, your circuit is so high-gain that you just have to play over the noise     You turn it on as you start playing...

If you experience oscillation in a pedal at LOW volumes, though, you should be able to do some of the above to limit the oscillation.

Wow thanks for your detail explanation. I will try again and hopefully it can be solved.