MK Sound MX-150THX, V-125THX, Operation Manual

THX  subwoofers

                                                    page 15

2.

If the midbass range (the area of transition between Subwoofer and Satellite or L/C/R
speakers) sounds weak:

See Section 7, PHASING TEST, on page 11.  Reverse the position of the "SUBWOOFER PHASE"

switch on the back panel of the subwoofer.  The switch position that gives the most bass is correct.

3.

If  you hear a thump through the subwoofer every time you turn the rest of your audio
system on (and your subwoofer is plugged in all the time):

Either the preamp, amp, receiver, or surround sound processor is generating the thump, and the

subwoofer is reproducing it.  Contact your dealer or the manufacturer of the other component.

4.

If you hear a persistent hum or buzz through the subwoofer:

Because the subwoofer easily reproduces 60 Hz signals (the frequency of hum), it is often blamed

for causing hum that originates elsewhere in the system.  Always avoid running all speaker wires and
RCA interconnect cables near to AC cords and component power supplies.  Placing wires and cables
close to AC lines often results in hum.  If necessary, reroute your cables.

To identify the source of hum, remove all input cables to the subwoofer, but leave it plugged into

the AC outlet.  Set the "BASS LEVEL" switch to the "VARIABLE" position.  Carefully turn the "BASS
LEVEL" control up towards the "MAX" position.  If you hear hum from the subwoofer, it is the source
of the hum.  If you hear no hum or much less hum, the problem is in another component or a ground
loop.

For ground loop problems,  when the subwoofer is plugged into a separate AC outlet, try plugging

it into the same outlet as your amplifier or receiver.  If that doesn't work, reverse the polarity of its AC
plug.  If you cannot solve the problem, call M&K or your dealer.

5.

If you hear an unusual sound from the subwoofer when no signal or music is playing:

Try removing the input cables as described in Step 4 above.  If the noise disappears, it is coming

from another component.  If it does not go away, contact your M&K dealer or the factory.

6.

If  the subwoofer will not play loud enough, AND it is connected to the SUBWOOFER
OUTPUT jack on a non-THX surround sound processor:

Make sure that the "BASS LEVEL" toggle switch is set to "VARIABLE."  Set the "BASS LEVEL"

control to the "MAX" position.  If you get bass output, but it is not enough, then the processor's output
level is too low.

Some surround processors/receivers/amps have very low output levels from their SUBWOOFER

OUTPUT jacks.  If you do not have enough gain when using the SUBWOOFER OUTPUT jacks on a
non-THX processor, use the processor's PREAMP OUTPUT jacks.  See Figures 5 and 6 (page 9).

IF YOU NEED TO REPLACE THE EXTERNAL FUSE:

First, unplug the subwoofer from the wall AC socket.  Remove the fuse cap.  Look carefully at

the fuse's wire filament inside the glass.  If it  is broken, replace the fuse ONLY with one identical in
size and value.  Using a larger fuse will void your warranty AND MAY CREATE A FIRE HAZARD.  Plug
the subwoofer back in.  If it does not work, unplug it immediately, and contact M&K or your dealer for
service.