Sunfire Home Theater System - Manual (Page 18)

18
5SERgS
Hum
Adding any component such as a sub-
woof er to an existing system will often
give rise to a hum which wasn’t there
before. Your fi rst thought may be that
the sub woof er 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 equip ment on
the same electrical outlet or circuit, see
page 9 for more details.
• If your sub woof er is a fair dis tance
away from your other equip ment, you
may use a 15 amp extension cord as
long as it has a ground con nec tion.
NOTE: Never remove the ground
pin from any power cords. This is
very dan ger ous.
• Turn off all components in your system,
including the sub woof er, amplifi ers and
the preamplifi er, before dis con nect ing
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 com mon problem to consider: a
“ground-loop” in tro duced by con nect ing
a cable TV line to a VCR or TV, which is
then con nect ed to the preamp. This can
be addressed as follows:
• Dis con nect all cables which come from
outside the room, such as cable TV,
satellite TV, or roof top an ten nas. Make
sure that they are dis con nect ed where
they fi rst enter the room, so they are
making no con nec tion to your pream pli -
fi er, TV, or any other component. If the
hum is caused by the cable TV line, then
you will need a “ground-loop iso la tor.”
This is an in ex pen sive device fi tted 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 preamplifi er 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
identifi ed which components are causing
a problem, you can fi t the isolators be-
tween the component and the preampli-
fi er.
The subwoofer won’t turn off
• The subwoofer should turn itself off after
ap prox i mate ly fi fteen min utes with no
audio signal present. If not, check there
is no back ground hum. The sub woof er
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 preamplifi er.
• Check the input connections.
• Check the mode switch or menu on sur-
round systems to be certain that a bass
signal is being sent to the subwoofer.
Audible snap from outlet
• When the sub woof er 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 sub woof er into a switched
outlet or switched power strip (rated at
15 Amps or more).