Well, this is driving me absolutely crazy. I would try to explain in relatively concise manner.
I'm aware that sound card (PC) and power amp can share only one electrical ground (either via RCA connectors or power sockets). If you have two electrical grounds in parallel, ground noise from the PC can be picked up by the amp. I believe that's what happening in my case. Interestingly enough, it's happening even when external DAC is in place! It's at worst when doing some intensive GPU tasks or GPU stress test (I have Radeon 290X), so I believe that GPU card is the culprit actually as it's badly designed. Anyhow, I didn't experiment with ground loop or USB isolators. Simply put, not enough experience and there are rumors that isolators are damaging the sound path.
I know that when using optical connection to the external DAC you are effectively isolating DAC/AMP from the PC pollution noise, but in my case I want to use sound card explicitly. So, how can one have only one ground plane when using PC sound card? I know that you can disconnect the ground wire from the power amp plug, let's say, but that's safety concern.
Is there any other work around? I have very good internal sound card and simply put want to avoid external DAC route at the moment.
Edited by Incognito73 - 6/3/14 at 5:22am