Amplifier Technologies, Inc. AT1800 Series Manuel du propriétaire - Page 10

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A Few Words About Hum and Noise

Audible hum, or a discernable low frequency noise, is one of

the most common problems in audio/video systems. This

hum, which may be present even when the volume is at a low

level, is usually caused by a problem known as "ground

loops". A ground loop occurs when there is a difference in

ground voltages between two or more components that are

connected electrically. This, in turn, creates multiple current

paths and causes the low-level noise, or hum.

The growing sophistication and complexity of home

audio/video systems, and the increased number of compo-

nents used to create these systems has dramatically increased

the potential for the possibility of ground loops. While it is

natural to suspect that the components in your system are the

cause of the hum, in many cases the cause may be due to

other conditions. In particular, cable TV connections from

outside the house have become a major source of hum.

In most cases, one of the following suggestions should help

you to solve a hum problem in your system. Please try these

steps in the sequence shown, proceeding from one step to the

next if the prior suggestion does not eliminate the problem.

Potential Ground Loops

in a Complex A/V System

Suggestion #1:

To determine if a cable TV connection is responsible for the

hum, first turn all components off. Disconnect the cable TV

feed to your system at the first place where it connects to

your components. Alternatively, disconnect the cable TV wire

where it is connected at the wall outlet. Turn your system

back on, and listen if the hum has disappeared. If removing

the cable TV feed has eliminated the hum, you will need to

insert a Ground Loop Isolator before reconnecting the cable

TV feed, or contact your cable TV operator to see if they can

better isolate your cable feed.

Suggestion #2:

Turn off all components in your system, and then disconnect

the input cables at the amplifier. Turn the amplifier back on,

and see if the hum is still present. If the hum disappears, the

fault may be in the input cables used. Try replacing them with

cables that have better shielding, and make certain that the

input cables are not running on top of any AC power cords.

Change the cables one at a time to determine if one, or all

cables is responsive. If the hum disappears when the input

cables are disconnected, but returns after the cables are

changed and the system re-connected, the problem may be

caused by your source device.

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Suggestion #3:

Ground loop problems may also be caused by poor grounding of

the electrical system in your home, particularly when there are

multiple components with three prong, grounded, power cords.

Try unplugging these components one at a time, and see if one or

all of them is causing the problem. The ultimate solution to this

type of problem is to re-wire your house with an isolated, star

type-grounding configuration. We recognize, however, that this

may be impractical and expensive. In some cases, the use of an

approved AC Power Isolation Transformer of sufficient capacity

may solve this problem.

WARNING: If you suspect that the grounding system in your home's

electrical wiring is causing the hum problem, it is important that you do

not make any changes to the wiring yourself. Only a licensed electrician

should make any changes to household wiring, and they must be made in

full compliance with all local building, safety and electrical codes.

Suggestion #4:

Hum may also be caused by faulty earth grounds in your home's

electrical system. In the past, cold water pipes were often used for

the earth ground, so it is important 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 in some locations

due to requirements that the water meter be isolated from the water

mains with a length of PVC pipe, thus interrupting the ground

circuit. The safest, and most reliable, approach may be to provide

your own ground. This can be accomplished by having a licensed

electrician drive at least five feet of copper-jacketed steel grounding

rod into the earth, and using that for your grounding connection.

If the hum persists after all of the above suggestions have been

tried, contact the ATI customer service department for assistance.

For Future Reference

Model Number______________________________

Serial Number ______________________________

Date of Purchase ____________________________

Where Purchased ___________________________

Notes _____________________________________

___________________________________________