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User's Manual
18
Hum
Adding any component such as a
subwoofer to an existing system will
often give rise to a hum which wasn’t
there before. Your first thought may be
that the subwoofer has a problem, but
this is more than likely caused by a
“ground-loop” in your system.
Follow these steps to isolate the main
cause of the ground-loop hum (there
may even be more than one cause).
• Try to have all of your equipment on
the same electrical outlet or circuit, see
page 9 for more details.
• If your subwoofer is a fair distance
away from your other equipment, you
may use a 15 amp extension cord as
long as it has a ground connection.
NOTE: Never remove the ground
pin from any power cords. This is
very dangerous.
• Turn off all components in your
system, including the subwoofer,
amplifiers and the preamplifier, before
disconnecting or connecting cables.
• First remove every connection from the
subwoofer to the rest of your system.
Plug the subwoofer power cord back in
and check for the hum. If it is still there,
try plugging it into a different outlet in
case it is picking up interference on the
AC line.
• If you have followed the above
guidelines for the power connections
and a hum is still present, then there is
one very common problem to consider:
a “ground-loop” introduced by connect-
ing a cable TV line to a VCR or TV,
which is then connected to the preamp.
This can be addressed as follows:
• Disconnect all cables which come from
outside the room, such as cable TV,
satellite TV, or roof top antennas. Make
sure that they are disconnected where
they first enter the room, so they are
making no connection to your preampli-
fier, TV, or any other component. If the
hum is caused by the cable TV line,
then you will need a “ground-loop
isolator.” This is an inexpensive device
fitted in line with the coaxial cable feed.
• If the hum persists, disconnect all the
source components one at a time from
the back of the preamplifier until you
identify the problem.
• If you are using the subwoofer’s Line
Level inputs and there is a excessive
amount of noise or hum present, using
the Speaker Level inputs may yield a
lower background noise level.
• Ground-loop isolators are available for
audio lines and video. Once you have
identified which components are
causing a problem, you can fit the
isolators between the component and
the preamplifier.
The subwoofer won’t turn off
• The subwoofer should turn itself off
after approximately fifteen minutes with
no audio signal present. If not, check
there is no background hum. The
subwoofer may sense hum as a small
signal and stay on. See the above hints
to eliminate the hum.
The subwoofer won’t turn on
• The subwoofer’s volume control may be
turned down or no signal is received
from your preamplifier.
• Check the input connections.
• Check the mode switch on surround
systems to be certain that a bass signal
is being sent to the subwoofer.
Audible snap from outlet
• When the subwoofer is initially plugged
into the wall, there is an in-rush current
surge as the power supply capacitors
charge up. This may give rise to an
audible snap from the outlet as the plug
is inserted. This can be avoided by
plugging the subwoofer into a switched
outlet or switched power strip (rated at
15 amps or more).