More often than not humming and buzzing through your speakers is caused
by a grounding problem. There are three main ground problems that cause
problems in an audio /
video system.
These are ground loops, improper grounding and lack of a ground
altogether. The other possible culprits that can cause noise are bad
cables, a faulty piece of equipment or electrical noise from a lighting
dimmer or electric motor. There are steps you can take to troubleshoot
the noise and eliminate it from your theater or entertainment system.
The first step to is to find out where it is coming from. Disconnect
your source and display equipment from your receiver or surround sound
processor. If the noise stops, connect them back to the receiver or
processor on at a time until the noise returns. When the hum comes
back, you found where the noise is entering your system. Note that if
you are connecting remote equipment, such as running the signal from
your theater room DVD player to the TV in the bedroom, your chances to
pick up noise increase dramatically. With such long runs, noise can be
induced into the long cable runs from adjacent electrical wiring. It is
also easy to create a ground loop, because the equipment is plugged
into two different, widely separated outlets, on different electrical
circuits.
If the noise is caused by a cable box, the noise is likely caused by
the cable TV ground. To test this theory, disconnect the incoming cable
TV feed to the rear of the cable box or TV while they are still
connected to the rest of the system. If the noise is eliminated by
disconnecting the
TV cable
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,
the problem is the cable TV ground. You can electrically decouple the
cable TV feed from your system with a ground breaking transformer.
These are available from many sources. Be advised that many newer,
digital cable TV
systems require any device in the signal chain to pass a full 1,000
Mhz. Some of the older ground break transformers will not do this. Be
sure to check the specifications of whatever device you are purchasing
to verify it will pass the digital cable
TV signal.
If the noise is from your projector, TV, or monitor, it is most likely
caused because the video display device is plugged into a different
outlet than the other a/v equipment. It could be on a different circuit
as well. These circuits may have two different ground potentials. That
is, the resistance to ground is different on each circuit. A difference
in resistance to ground from one ground point to another can cause the
dreaded ground loop. If you get a ground loop, current flows between
the two components. If the current flows through the components
internal audio signal ground, you will get a hum.
You can use an isolation transformer, similar to the type used for
cable TV ground problems, to eliminate the electrical connection from
one component to the other. These transformers are inserted in line
with the audio signal connection between the two components. If there
is no audio connection between the components, the problem may be
current flowing through the video portion. In this case, a video
isolation transformer should be used to eliminate the ground loop.
Sometimes power conditioners will stop noise problems by placing
equipment on different, electrically isolated outlets. This is done
using isolation transformers. This can be ineffective however, due to
the differences in internal construction of different power
conditioning equipment. Some safety regulations, such as UL 1950,
specify that an isolation transformer is only allowed to isolate the
hot and neutral wires; the grounding wire must be passed straight
through. If this is the case, the ground loop problem may still exist
because many communication circuits are connected to the grounding
conductor and not the neutral. In this case, the isolation transformer,
or any power conditioner or UPS with an isolation transformer will have
absolutely no affect on the grounding problem.
The noise may be generated externally, from a dimmer or refrigerator
compressor for example, and coming in through the main power input on
the
audio video equipment
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.
In this case, a high quality power conditioner may be effective in
reducing or eliminating the noise problem. You may also find that one
of the signal interconnecting cables in your system is faulty. This can
also cause noise problems. Check for this by swapping the cables with
one that you know to be good.
You can solve most noise problems in your home theater or multi room
audio/video system by taking the systematic, step-by-step approach.
Work your way up the signal chain, eliminating each piece of equipment
as you go. If you have nothing connected to your speakers except the
speaker wiring, and they still hum, the problem is noise induced into
the speaker wiring from adjacent power cables. Other than that case,
most problems are caused by ground problems, which you can find, and
solve, if you take it one step at a time. Hope this helps. Let me know if I can help you with anything else.
JimmyC
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