Quantum Mystic low gain issues

[Domin]

Hi, i just made BAT Quantum Mystic as a preamp for my amp project and i want to ask. It has 2 switchable gain pots, one 500K like original and one 1M to get lower gain sounds, like "2 channel" and even when i turn 1M pot down do minimum, i can hear realy quiet distortion behind clean signal, like 2 separate tones...how can i get rid of it? Any ideas? Its really quiet but its still there

[Elijah-Baley]

Can you show us how you modified the schematic with this second pot?

[Domin]

This was first wiring (different values)


Later i tried this




Both have same issues...but when i turn input volume of poweramp down, it wasnt that loud, could it be that poweramp is clipping? PAM8403

[Elijah-Baley]

I figured the first method worked, but even the second one does.

Do you have this issue just when you add the second pot? When you totally take it off do you hear anything wrong? (In theory, the switch should already disconnect totally the pot from the signal, keeping it to the ground shouldn't do anything).
I'm wondering if there's any other mistake.

[Elektrojänis]

Does the quiet background distortion change when you switch between different diodes with SW1?

It also might be usefull to try this preamp part with a known good amp or the poweramp of this build with a known good clean preamp.

[Domin]

I didnt use diode switch. I just wanted high gain like original and less gain to make like clean signal, even when its set to clean, i hear distortion, could it be that like first part of signal is clean and distortion happens in tonecontrol? When i turn all tone knobs at noon its less noticable than when i max bass, mids or trebles...I didnt try just one pot, but i can try it.

[Domin]

Here is audio, even on it i can hear it...when i turned volume almost completely down, it was gone https://youtu.be/bdUv1nL3o3s

[Domin]

This is when i tried to run signal just thru tonecontrol stage https://youtube.com/shorts/SztZDEOQdNo?feature=share