BrianGT chipamp loud buzzing when connected to PC

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I put together a BrianGT LM3886 chipamp a few months back, it's regulated and snubberized, but now I have a big problem. When I connect it to my PC I get this very loud buzzing sound on both channels, and I mean VERY loud. There is no buzzing when the amp is connected to a portable mp3 player or a portable radio (for testing, don't crucify me again :)
Logic tells me that there is a problem with ground, because the mp3 player runs on batteries and the radio is not connected to mains ground at all (no 3rd pin), while the PC is.

I did hear some very slight buzzing in the last month or so, but I thought it had to do with the toroid buzzing, and that recasing the PS would do, but this is obviously something else.

Any thoughts on what I should check?
 
I normally use DIY 1/4inch to RCA from my EMU 1212 soundcard to amp, but I tested with commercial cables too, and tried using the onboard soundcard - it's always the same.

Now, I tested a few setups, and it turns out that when the amp is plugged to a normal wall socket the loud buzzing is there, but when I plug it to an unearthed one (no 3rd pin), I only hear some slight buzzing. And that is ONLY when it is connected to the PC.

Could this be a problem if my apartment's mains is "nulled" (is that the word?) - when the neutral wire is connected with the earth wire?

And bcmbob - are you saying that you had a short on the plug? Did it fry the amp or what?
 
No, I did'n have any damage, The noise I had was due to one of the two wires not being connected - opposite of short. Have you tried the amp far away from the computer. My GTs are unusable within 1 - 2 feet of my desktop. They are under a thin aluminum cover but the interference still gets through.

The only other thing I can think of is try a ground wire from the case of the computer to the case/base of the Amp.

A few pictures of your setup would be very helpful.
 
Check if your computer is properly earthed. Measuring AC across the power socket earth and the computer chassis/black 0V wire you shouldn't be seeing more than a few mV. (Measure both chassis and black wire - although they are usually connected, sometimes they aren't.)

Could this be a problem if my apartment's mains is "nulled" (is that the word?) - when the neutral wire is connected with the earth wire?

Nope, neutral may be connected to earth outside your house to keep the neutral @ earth potential and hence keep it safe. And neutral will never be connected to earth inside your house as that will render ineffective the ELCB/RCD breaker.
 
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