22 hours ago, kevin gilmore said:

the resistors are just there to make sure its stable with nothing plugged into it.

change the input resistors to as low as possible compatible with what is going to drive it.

10k is probably what i would do.

Thanks, Kevin.

At the moment I only had 50kΩ resistors on hand. After replacing the input resistors with 50kΩ, the background noise is almost completely gone. There's still a very slight hiss/current noise, so I may also try adding a small pF-range capacitor to ground for some additional RF filtering.

I also noticed something a bit strange with my layout. On my board, installing the 470pF capacitor causes the output voltage to rise very close to the raw DC rail, whereas using a 5pF capacitor doesn't cause that behavior. I'm not sure if it's layout-related or if I've made a mistake somewhere.

Has anyone else run into this issue with their build?

the 470pf cap is on the power supply right?

the reason for the 1 meg input caps is to give a minimum stable bias for the input stage. its expecting you to put in front of it a pot, or other much lower impedance resistor.

at 50k the remaining noise is far below any possible music at that level that does not significantly lower the input impedance.

Edited 44 minutes ago44 min by kevin gilmore