Actually this text is written for
german visitors. Some references to the german power
and cable system are made. Perhaps it is not transferable
into your situation.
If one connects a stereo amplifier with the computer using an
audio cable sometimes a bothering, humming noise is coming
out of the loudspeakers. This is caused by a so called 'ground loop'
(Actually this is a translation of the german word 'Erdschleife'.
another common word for this is humming loop 'Brummschleife').).
There are several possible reasons for such a loop. Often
the "misfortune" starts after the PC is connected to the hifi
equipment or a new subwoofer gets connected to the stereo amplifier.
This article likes to explain the causes and offers a small, cheap
circuit that solves the problem easily.
Different causes for the ground loop
Actually the causes and reasons how a ground loop is
generated are quite complex. Sometimes it also depends on the cabeling in your
household and how the electrical devices are connected together. Devices
grounding over the electric power supply system are often the
source for "trouble". Additionally all devices with antenna connectors also are
often causing trouble because the coaxial outer conductor is connected to
antenna ground. In most cases devices like satellite receivers, tuners and VCRs
are connecting to antenna ground with the antenna cable.
What is the electrical background of a ground loop?
We are talking about a ground loop when there is a big, conducting loop.
It can look like the following example
Computer with audio card, audio cable,
HIFI amplifier, tuner, TV, VCR ... etc.,
antenna cable, house main equipotential bonding,
power supply ground wire, computer
In the "classical" case this big loop is behaving like a
"transformer with one coil". This "transformer" receives the magnetic
leakage field of the electrical power supply system. If you
are living near long-, medium or short wave transmitters sometimes
radio stations are also 'picked up'. Often this causes very annoying
This inducted tension is overlaid with the wanted audio signal
on the audio connection between computer and stereo amplifier (The outer conductor
of the audio connection is part of the big loop in the above example). This
causes the audible humming noise.
As a transformer needs a low-resistance conducting loop an
interruption of the loop is sufficient to end the humming. Please
see on the right side for a small filter for your antenna connection.
Variant 2: Old buildings and old installations
I removed this part in the 'international' (english) part of this document.
It is specific for germany (Electrical cabeling, security measurements,
labeling of cables, power plugs etc.).