Noise, oscillation? In bog standard volume control.

[marcelomd]

Hi,
I've built a version of my MOSFET preamp with a slightly different output stage. The volume control works as it should but at minimum it gets very noisy. Like oscillation, but in the lower mids, not high pitched. Both channels, high and low gain have the same issue, with exact same noise.

Why would it do it?

This is inside the box, with proper grounding and all. Only other thing connected is a headphone amp/digital IR loader.

Thanks!

[GibsonGM]

Are the leads separated enough from each other?  I've had these issues with high gain mosfet stuff, to the point that I don't make them anymore - they seem susceptible to oscillation.  Maybe needs a snubber cap or 2?

[marcelomd]

How far is far enough?

The one on top, clean channel, is currently mounted with 2 stages only, so not that high gain.

Maybe I should split the ground plane in 2?

[GibsonGM]

Insufficient experience in making PCBs, Marcelo - following! I usually do point to point on perfboard.  Did you breadboard it first?

By separating leads, I mainly meant offboard, from in jack to switch, switch to output jack etc., and shielded wire on input.  Maybe you can isolate where it starts with an audio probe?

[marcelomd]

I'm at a point in my life that ordering assembled boards from JLC is cheaper than doing it at home.

This is the 3rd or 4th version. First with this output stage design and this problem.

The offboard wiring is the same as the others. Like exactly the same as I soldered pin connectors to the board and left the jacks fixed in the box.

[GibsonGM]

I'm sure you've swapped out the FET...