User Guide
8
A-2000 7 Channel Amplier
Instruction Manual
9
Potential Ground Loops in a Complex A/V System
Suggestion 1 To determine if a cable TV connection is responsible for the
hum, rst turn all components off. Disconnect the cable TV feed to your
system at the rst place where it connects to your components. Alternatively,
disconnect the cable TV wire (not the AC wire to the cable box, but the cable
antenna 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. Ground Loop Isolators should be
available from your local Audio Video dealer.
Suggestion 2 Turn off all components in your system, and then disconnect
the input cables at the amplier. Turn the amplier 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 or directly adjacent
to and parallel with any AC power cords. Change the cables one at a time to
determine if one, or all cables is responsible. 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 processor,
receiver or preamplier.
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 conguration. We recognize, however, that this
may be impractical and expensive. In some cases, the use of an approved AC
Power Isolation Transformer of sufcient 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 connec-
tion 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 ve feet of copper-jacketed steel grounding
rod into the earth, and using that for your grounding connection.
Suggestion 5 If you have hum in your video display device (bars that roll up
through image at 12-14 second intervals), this may be related to hum you also
experience in your audio system. The previous suggestion tips may help with
this also. If not, try isolating the ground in the projectors video signal cable
with a base-band video isolation transformer, such as the Jensen VB-1BB.
If the hum persists after all of the above suggestions have been tried, contact
our customer service department for assistance.
A Few Words About Hum and Noise
60Hz AC
Ground
60Hz AC
Ground
AC Ground
AC Line
A/V Cables
Main House
Grounding
Cable Feed
Coax Cable
Ground Loop Diagram
AC Line