Amplifier Tech AT1800 Series Stereo Amplifier User Manual

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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.
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.
For Future Reference
Model Number______________________________
Serial Number ______________________________
Date of Purchase____________________________
Where Purchased ___________________________
Notes _____________________________________