"Bill D." said:
Thanks for the in depth response Paul, you may have hit the nail on the
head. I do indeed have a plug converter on the wall outlet (live in an old
apartment with only a couple of 3 prong plugs, none remotely close to the
computer) and have plugged in a power bar that has 3 prong plugs in it.
I'll have the landlord get his electrician to install a properly grounded 3
prong plug for the computer and see if that makes a difference. If it
doesn't, then perhaps Markus' post will be correct at which point I'll be
looking into buying a sound card.
My parents live in an old house like your apartment. The wall
sockets are all the two prong variety. When I installed a
computer there, what I did, was buy an expensive power
strip that happened to have a green safety ground screw on
the side of the power strip. Got some heavy wire (maybe 14ga?)
from the hardware store, plus a clamp. Placed clamp on the cold
water pipe, under the sink. Ran a long wire from the sink, to the
fixed location of the computer. The power strip plugs into the
wall with the 3-to-2 adapter, and the piece of wire that runs
to the cold water pipe, provides the ground. Uses a crimp
connector, to provide a nice circular contact plate to meet
the head of the screw.
I doubt this meets electrical code, but it was the best I could
do, to prevent a shock hazard. Obviously, if there is a power
supply failure, where the hot wire gets shorted to safety
ground, that path to the cold water pipe had better be low
impedance, so the breaker trips before something burns. In
a house, it is relatively easy, to go to the basement, and see
whether the proper jumper wire, is used to jumper the cold water
distribution on one side of the water meter, to the copper
pipe coming in from the street. Having the electrician look
into this, in an old apartment, would be a good thing to do,
as who knows whether there is any adequate ground structure
in the apartment to wire to.
At least temporarily connecting this ground wire, from a
cold water pipe, to safety ground, would indicate whether
this is where the hum problem comes from. (I.e. When there
is no ATX power supply failure, the current flowing in the
wire will be tiny. Connecting a wire to the cold water,
then running it over to the computer, to ground some of the
case metal momentarily, may indicate whether a more permanent
connection via the electrician will improve things or not.
When handling the wire and the computer, don't make yourself
part of the circuit. Handle the wire by the insulation while
touching it to the case of the computer, just in case. I've received
a respectable shock in an industrial situation, from
improperly implemented safety grounds, so don't join the
club.)
In theory, another solution would be if ATX power supplies
did not have a common mode filter on their input side. That
filter is what leaks current into safety ground. But, if
that filter was removed, the electrical interference would
make it impossible to watch TV in your apartment. So, it is
a necessary function, and in some cases, an expensive
power strip that contains its own version of the filter,
can even improve the often inadequate size of the filter
used in the ATX supply. As long as one or more of those
filters is involved, the 60Hz current that leaks through the
filter has to go somewhere, and that is the convenient
path provided by the safety ground.
[ Don't accept electrical wiring advice off the Internet
Just like you wouldn't accept medical advice off the net.
You've been warned... The electrician is your friend. ]
HTH,
Paul
