Amplifier Tech manual From the Plug Used with the AT6012-SEVERE Shock MAY Result

Notes On “Hum”

With the growing sophistication of home theater systems, the potential for ground loops is enormous. Do not automatically assume that one or more of your components are at fault, or even defective. Lately, one of the biggest culprits is the Cable-TV incoming signal line.

Almost 100% of the cases where hum has been a problem have been due to one or more of the below conditions. The following notes will help you to determine its cause:

Note 1:

Cable TV systems can sometimes contribute to ground loop problems which cause hum. To determine if your cable system is the contributing factor, disconnect the Cable TV incoming signal line (round 75 Ohm) at the wall, or the first component the cable is connected to (i.e. the cable box, or VCR). If the hum is no longer present, you must insert a 75 Ohm Ground Loop Isolator before reconnecting the line. You should check with your ATI dealer to obtain one. If the 75 Ohm Ground Loop Isolator works only partially, or not at all, then please read Note 2, Note 3 and Note 4.

Note 2:

Turn the system off and disconnect all inputs from the amplifier. If the hum persists, consult with your dealer or ATI directly. If the hum disappears, try another set of input cables. Connect one cable at a time to see if one specific cable is responsible. If any or all cables cause the hum to appear, then your preamp or processor should be evaluated for proper operation.

Note 3:

When there is an audible “hum” through your loudspeakers, even with the volume control low or off, you have a common problem known as a “ground loop”. A “ground loop” is basically a difference in ground voltages between two or more components which are connected electrically and which creates multiple current paths where there should be only one. This difference in potential causes a low-level noise we call “hum”. AC ground-prong loop produces a fairly loud hum. When installing a system that uses three-wire AC cords with grounding-type plugs, note the units that have them. An installation that has two or more components that use a 3-prong plug may result in a ground-loop situation. If it is impractical to rewire your house with an isolated star ground configuration, you may want to try a power isolation transformer.

WARNING: DO NOT, UNDER ANY CIRCUMSTANCES LIFT THE GROUND (eliminate the round, 3rd prong)

FROM THE PLUG USED WITH THE AT6012–SEVERE SHOCK MAY RESULT!

Note 4:

Hum may also be caused by faulty earth-grounds from your house. In the past, cold water pipes often were relied upon for earth ground. Check to make sure that your ground connection is still valid and has not become loose or corroded. The cold water pipe method may no longer be valid because some municipalities require that the water meter be isolated from the water mains with a length of PVC pipe, thus interrupting the ground. The safest and most 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 problem, we suggest you call an electrician or your local electric company to inspect/repair the problem.

If the hum still persists after you have tried ALL of the above, please contact your dealer or ATI’s Service Department.

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