PC (GPU or CPU) interference on audio interface

[AnalogSteph]

What I/O on the Minitaur were you using in that case, and what is that going to? I see it's got a MIDI input and USB MIDI, for example, either of which could be introducing a ground loop (not to mention the analog audio input). The 12 V power supply is of the 2-prong plug pack type, I assume.

It's silly that this unit only has an unbalanced output jack, making it impedance-balanced would have been trivially easy at the design stage (making the jack TRS + 1 resistor + maybe 1 electrolytic capacitor, typically). Oh wait, according to the teardown pics the output is unbalanced stereo... OK, then obviously that wouldn't have been an option. I've tried to enhance the picture but still can't quite make out the resistor labeling, unfortunately. If you want to make an adapter cable that balances the output, you may have to break out the multimeter or sharp-eyed camera (or magnifier / old manual wideangle lens in reverse) with light at the right angle first and hope for about 1 kOhm or less.

Looks like a 4-digit code.

I would arguably prefer the multimeter route as it would allow selecting resistors from a bunch of candidates that are matching well with what's on the board.

 

[Izaac]

What I/O on the Minitaur were you using in that case, and what is that going to? I see it's got a MIDI input and USB MIDI, for example, either of which could be introducing a ground loop (not to mention the analog audio input). The 12 V power supply is of the 2-prong plug pack type, I assume.

It's silly that this unit only has an unbalanced output jack, making it impedance-balanced would have been trivially easy at the design stage (making the jack TRS + 1 resistor + maybe 1 electrolytic capacitor, typically). Oh wait, according to the teardown pics the output is unbalanced stereo... OK, then obviously that wouldn't have been an option. I've tried to enhance the picture but still can't quite make out the resistor labeling, unfortunately. If you want to make an adapter cable that balances the output, you may have to break out the multimeter or sharp-eyed camera (or magnifier / old manual wideangle lens in reverse) with light at the right angle first and hope for about 1 kOhm or less.
View attachment 467754
Looks like a 4-digit code.

I would arguably prefer the multimeter route as it would allow selecting resistors from a bunch of candidates that are matching well with what's on the board.

I tried MIDI and i noticed that there was less nosie, but i am using USB midi.

 

[AnalogSteph]

Then your ground loop most likely stems from that. Since you have a USB isolator, you can try it there.

My hunch is that you may have a whole maze of ground connections among your stuff and galvanic isolation may be required in more than one spot in order to clean it all up.

 

[Izaac]

@AnalogSteph Yes, it looks like and thats why i ordered also 4xADUM3160 - USB filter, but when i connect 4 synths on one USB its not that efficient in removing noise as a single unit, which somehow makes sense as the noise is added up 4 times.

The internall soundcard is propertly isolated and has no noise. As this is my second mobo, I have a feeling that USB ports are should be better isolated.
I will experiment arround to find the sweetspot and may be buy a new PSU, to check if that helps.