On Thursday 08 December 2005 00:04, Brian Rudnicke wrote:
Hi all. I've just moved in to a new home. In my old home, I had a
computer in my entertainment center which had a cable that ran from
the soundcard to the TAPE input on my Harmon/Kardon amp. It used to
play MP3's through there just fine.
Now that I've moved, whenever I connect anything computer related to
any of the inputs, I get a humming sound comming from the speakers.
It goes away when I take away the device.
You either have a common-mode earthing problem or something isn't grounded
correctly.
Check out these :-
1. All equipment used concurrently is connected to the the same supply
subcircuit. i.e. it is all connected to the same outlet or if more than one,
they are all connected to the same incoming feed from the
utility/fuse/circuit breaker box. In the unlikely event that both supply
phases are used for different circuits, make quite sure that everything
intended to work together is on the same phase.
2. Verify that the polarity of the supply is correct (may be the hot and
neutral are swapped on one socket). If wrong, correct it. NOT by just
reversing the plug!!
3. Verify that earth (ground in the US!!) is connected to the outlets used
to power the equipment and is of low impedance (less than 1 ohm) to true
ground at the incoming supply to the house. If not, fix it immediately,
since this is a potentially dangerous condition.
4. Screens used on cables must be connected (to ground) at one end only.
Grounding both ends may cause hum.
5. Verify that, during the move, a cable screen or ground/earth connection
hasn't broken somewhere, leaving equipment "floating".
6. If different cables have been used, make sure that anything wanting a
grounded (3 pin/prong) supply connection is plugged into a 3-hole socket,
correctly grounded. Using equipment intended to be grounded by the makers on
an ungrounded supply is potentially dangerous, so fix anything found.
HTH James :-)
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