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Thump18S Powered Subwoofer
Appendix A: Service Information
Poor bass performance
• Check the polarity of the connections between the
mixer and the subwoofers. You may have your
positive and negative connections reversed at one
end of one cable, causing one subwoofer to be
out-of-phase with the other.
• Poor bass performance may be the result of bad
AC power. See the section titled ‘AC Power’ on
the previous page for further details.
Poor sound
• Is it loud and distorted? Make sure that you’re not
overdriving a stage in the signal chain. Verify that
all level controls are set properly.
• Is the input connector plugged completely into
the jack? Be sure all connections are secure.
Noise
• Make sure all connections to the active
subwoofers are good and sound.
• Make sure none of the signal cables are routed
near AC cables, power transformers, or other
EMI-inducing devices.
• Is there a light dimmer or other SCR-based device
on the same AC circuit as the Thump18S? Use an
AC line filter or plug the subwoofer into a
different AC circuit.
Hum
• Try disconnecting the cable connected to the
input jack. If the noise disappears, it could be
a “ground loop,” rather than a problem with the
Thump18S subwoofer. Try some of the following
troubleshooting ideas:
• Use balanced connections throughout your system
for the best noise rejection.
• Whenever possible, plug all the audio equipment’s
line cords into outlets which share a common
ground. The distance between the outlets and the
common ground should be as short as possible.
If you think your Thump18S has a problem, please
check out the following troubleshooting tips and do
your best to confirm the problem. Visit the Support
section of our website (www.720trees.com) where you
will find lots of useful information such as FAQs and
other documentation. You may find the answer to the
problem without having to part with your subwoofer.
Troubleshooting
No power
• Our favorite question: Is it plugged in? Make sure
the AC outlet is live [check with a tester or lamp].
• Our next favorite question: Is the power switch
on? If not, try turning it on.
• Make sure the line cord is securely seated in the
line cord socket and plugged all the way into the
AC outlet.
• Is the power LED on the front and rear panel
illuminated? If not, make sure the AC outlet
is live. If so, refer to “No sound” below.
• The internal AC line fuse may be blown. This is
not a user serviceable part. If you suspect the
AC line fuse is blown, please see the "Repair"
section next.
No sound
• Is the level knob for the input source turned all
the way down? Verify that all the volume controls
in the system are properly adjusted. Look at the
level meter to ensure that the mixer is receiving
a signal.
• Is the signal source working? Make sure the
connecting cables are in good repair and securely
connected at both ends. Make sure the output
level control on the mixing console is turned up
sufficiently to drive the inputs of the speaker.
• Make sure the mixer does not have a mute on or a
processor loop engaged. If you find something like
this, make sure the level is turned down before
disengaging the offending switch.
• Has it shut down? Make sure there is at least
six inches of free space behind each Thump18S
subwoofer.
