How to prevent amplifier from picking up interference from computer? - Page 4

Use external USB soundcard like EMU 0404 USB to solve the issue. 

Also use optical connection and not coax  from computer audio to EMU if you want to isolate from computer EMI even further. Probably not necessary though.

Since the problem is a ground loop, and not EMI, USB will only fix it with an isolator, and optical S/PDIF is definitely preferred over coaxial. As already mentioned, there must be at most one ground connection between the PC and the amplifier, either through the AC power cords (and using optical S/PDIF or USB with galvanic isolation, or an audio transformer), or through the audio interconnects (with a non-grounded amplifier, or other means of breaking the AC ground connection), but not both.

I've run into this problem quite a bit. First on my home PC when I went to hook up my PC to my home stereo. Horrible noise from EMI, impedance mismatch, and ground loops. I saw this item http://www.dak.com/Reviews/2045Story.cfm and was skeptical. Upon getting it (was like $15 back then I think), and upon receiving it I thought it looked like absolute trash and thought this piece of junk could not work. I was SOOOO wrong. All that noise, GONE, instantly. Worked like a dream. Have been running on one of these for like 5 years now. At my church we have a number of PC's hooked up to a rather nice sound system. The house audio amplifiers put out something like 12,500 watts total output, and the system sounds quite good. The same basic problem occurred, horrible sounding audio, and constant hum/buzz/pops. Just miserable sounding. I mentioned these things, we ordered them, now for like double the price, and voila. Totally worth the $30. Our one PC used for sermon audio recording actually has a nice stand alone sound card in it. It did not matter (though I guess that was for audio input). Anyway if you are not looking for idealistic audiophile solution to make your sound perfect, I betcha the above device would work. Now with my stereo system on at about 50% volume and hooked up to my PC's motherboard audio output, there is no detectable "noise" difference than when I have the Stereo in CD mode and the volume at the level with the CD stopped. So all the noise that is noticeable now is inherent to my stereo.