As Mark says, we need to see they power layout. What parts have power and what parts have a power ground?
Power ground means Earth? I don't have Earth ground in my house. So I should cut off the signal ground between DAC and amp, connect only one wire for each channel?
You don't have power earth at all in the house? So your plugs look like the one above on the left?
Well I don't think you have a ground loop problem, as nothing is grounded!
It could be that your neutral is connected to earth, and that might be causing trouble like a ground loop.
It could be that your neutral is connected to earth, and that might be causing trouble like a ground loop.
You can always give the ground lift a try. If it is RCA (cinch) connector try just connecting the tip of the RCA to your DAC or amplifier. If there is no ground between the two, you will get a loud buzz. If there is a ground between the two, you should hear music without a very loud buzz.
yes, I think so, because the PSU of my computer have two capacitors connected between live, neutral and earth, maybe that's the problem(because no Earth wire in my building), and most of the PSU have these capacitors too. Maybe I will try the USB isolator ic or remove those capacitors, and will update the post if the problem is fixed. Thanks for your replies.
Yes, I know it must be common grounded between dac and amp, so I ask if the audio transformer can solve the problem or not, and after the discussion with you, I think usb isolator would be a better solution, since the problem may cause by the computer and the fridge, so isolate the usb port maybe more suitable in my case.