[sdiy] Protective Earth on PC soundcard GND?

[Ingo Debus]

Am Donnerstag, 27.01.05 um 21:40 Uhr schrieb Magnus Danielson:

>>
>> (I still have this unexpensive M-Audio Delta 1010LT in mind, but I'm 
>> also
>> asking if there is a general convention of connecting, or not 
>> connecting GND
>> and PE in a PC ausio system.)
>
> Ground should be connected at all times, but with real balanced 
> systems you may
> cut it when that aids in lowering the hum.
>

Just checked it. Yes, the 1010LT's audio ground is connected to the 
ground of the computer, and thus to PE.
IMHO so so much the fault of that sound card. It just connects its 
audio ground to the power supply's ground. The main culprit is the 
computer and its connection from signal ground to PE. But pretty much 
all (desktop) computers do that.
Not much of a problem here, since the computer is my only piece of gear 
with a signal-ground-to-PE connection. The ground loop formed by the 
1010LT and the computers own audio output (Mac G4) is worse.

I really don't know why so many devices have signal ground and PE 
connected. It causes ground loop trouble all the time. (I take no 
responsibility if anyone modifies their gear because of the above 
sentence, blah, blah, blah :-) But seriously: don't disconnect PE from 
the chassis. Better try to disconnect signal ground from the chassis).

Years ago I had a quite heavy argument with someone who claimed that 
every touchable part of a device a mains cord with PE has to be 
connected to PE (and thus signal ground of course too). But what about 
a guitar amp with a cable plugged into its input? What about the tip of 
the plug at the other end of the cable? No doubt its touchable, so the 
input has to be grounded, eh??

Ingo