Notes On “Hum”
With the growing sophistication of ho e theater syste s, the potential for ground loops is enor ous. Do not
auto atically assu e that one or ore of your co ponents are at fault, or even defective. Lately, one of the biggest
culprits is the Cable-TV inco ing signal line.
Al ost 100% of the cases where hu has been a proble have been due to one or ore of the below conditions.
The following notes will help you to deter ine its cause:
Note 1:
Cable TV syste s can so eti es contribute to ground loop proble s which cause hu . To deter ine if your cable
syste is the contributing factor, disconnect the Cable TV inco ing signal line (round 75 Oh ) at the wall, or the
first co ponent the cable is connected to (i.e. the cable box, or VCR). If the hu is no longer present, you ust insert
a 75 Oh Ground Loop Isolator before reconnecting the line. You should check with your ATI dealer to obtain one.
If the 75 Oh Ground Loop Isolator works only partially, or not at all, then please read
Note 2, Note 3
and
Note 4
.
Note 2:
Turn the syste off and disconnect all inputs fro the a plifier. If the hu persists, consult with your dealer or ATI directly.
If the hu disappears, try another set of input cables. Connect one cable at a ti e to see if one specific cable is responsible.
If any or all cables cause the hu to appear, then your prea p or processor should be evaluated for proper operation.
Note 3:
When there is an audible “hu ” through your loudspeakers, even with the volu e control low or off, you have a
co on proble known as a “ground loop”. A “ground loop” is basically a difference in ground voltages between two
or ore co ponents which are connected electrically and which creates ultiple current paths where there should
be only one. This difference in potential causes a low-level noise we call “hu ”. AC ground-prong loop produces a fairly
loud hu . When installing a syste that uses three-wire AC cords with grounding-type plugs, note the units that have
the . An installation that has two or ore co ponents that use a 3-prong plug ay result in a ground-loop situation.
If it is i practical to rewire your house with an isolated star ground configuration, you ay want to try a power
isolation transfor er.
WARNING: DO NOT, UNDER ANY CIRCUMSTANCES LIFT THE GROUND (e iminate the round, 3rd prong)
FROM THE PLUG USED WITH THE AT6012–SEVERE SHOCK MAY RESULT!
Note 4:
Hu ay also be caused by faulty earth-grounds fro your house. In the past, cold water pipes often were relied upon
for earth ground. Check to ake sure that your ground connection is still valid and has not beco e loose or corroded.
The cold water pipe ethod ay no longer be valid because so e unicipalities require that the water eter be
isolated fro the water ains with a length of PVC pipe, thus interrupting the ground. The safest and ost reliable
approach is to provide your own ground. Drive at least five feet of copper-jacketed steel grounding rod into the earth
and use that for the ground. If you suspect a grounding proble , we suggest you call an electrician or your local
electric co pany to inspect/repair the proble .
If the hu still persists after you have tried ALL of the above, please contact your dealer or ATI’s Service Depart ent.
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