Sunfire HRS-12 - Manual (Page 18)

User's Manual
18
Hum
Adding any component such as a sub-
woofer 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, pro-
vided that the total current draw does
not exceed the current safety rating of
the outlet or circuit.
• 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.
• Turn off all components in your system,
including the subwoofer, amplifiers and
the processor, 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 guide-
lines for the power connections and a
hum is still present, then there is one
very common problem to consider: a
“ground-loop” introduced by connecting
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
processor, 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 processor until you iden-
tify the problem.
• If you are using the subwoofer’s line-
level inputs and there is a excessive
amount of noise or hum present, try us-
ing the speaker-level inputs as they 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 be-
tween the component and the preamp.
No auto 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.
No auto turn on
• The subwoofer’s volume control may
be turned down or no signal is received
from your processor.
• Check the input connections.
• Check on surround systems to be cer-
tain that a bass signal is being sent to
the subwoofer.