[DasKobold]

The fact that a DAC is USB-powered won't help there. But the amp seems to be the issue in your case.

But there seems to be something wrong with my DAC too, because I tested my DAC solo first, amp only arrived today. Actually, let me explain it using pictures.

First I connected my DacMagic 100 to my g5 soundcard (this was last week, I had no amplifier at that point)

DacMagic was connected to my PC using usb, and the dac itself was connected to my computer using the cable in the picture. Dac's output to soundblasters input. Then I connected my headphones to the soundblaster. On my computer I could then choose the default play device. If I chose the DAC Magic the sound was louder, and different, but I also heard that weird peep constantly. If I chose the soundblaster as default in my computer settings the peep would go away, obviously because it now ignored the dac.

I thought maybe this DAC didn't like my soundcard, so I connected it to my other soundcard

Used a different cable this time wanted to know if there is maybe something wrong with the cable. Also, the previously used cable doesn't work on that soundcard. It was the same result, peeping was still there. I thought maybe the new amplifier would help.

So today my new amp arrived (Musical Fidelity V90-BHA)

And yeah, now I am hearing this ground loop thing. Well, let me first explain how I connected this. DacMagic 100 is connected to PC using USB and via that cable in the picture it's connected to my amplifier (Musical Fidelity V90-BHA). And this combo sounds horrible. I mean it probably would sound normal if it wasn't for that ground loop thing. So I chose the option to send the DAC back on amazon, thinking it was broken and ordered the MODI 2 instead.

Well anyway, I tried one more thing

Earlier today I connected my soundblaster g5 to my Musical Fidelity V90-BHA. The g5's output is connected to the amplifiers input, and my headphones are connected to the Musical Fidelity V90-BHA phone jack thing in the front. And this sounds just as bad as if it was connected to the DAC. I then tried one more thing, I disconnected the amp entirely from my soundcard. I went into a different room, plugged it into a new socket and only connected my headphones to it. The ground loop sound was not as load as before, but still there.

I hope the pictures make it more clear.