MACKIE MR8MK2 - Manual (Page 8)

8
MR8mk2
MR8mk2
Protection Circuits
Input Signal Wiring
You should use high-quality, shielded cable to connect
the signal source to the signal input jack [1] on the
MR8mk2.
• For balanced signals, foil shielded cables, such as
Belden 8451, 8761, or 9501 are commonly used for
studio wiring.
• Microphone cables work well for the XLR input.
• The better the shield, the better the immunity from
externally induced noise (like EMI and RFI). Route the
cable away from AC power cords and outlets. These are
common sources for hum in an audio signal. Wall warts
and line lumps are especially insidious hum inducers!
Quality cables may be purchased from Mackie dealers.
• In certain home theater applications, it may be necessary
to connect the speaker outputs from a stereo receiver to
the inputs of the MR8mk2, if the receiver doesn’t have
preamp outputs or other line-level output connections.
CAUTION: Do not attempt to connect a
speaker output directly to the input of the
MR8mk2! Speaker levels are much higher
than line levels and can damage the input circuitry in
the MR8mk2.
However, it is possible to insert a speaker-level to
line-level signal attenuator between the receiver’s
speaker output and the MR8mk2’s input. The local
Mackie dealer should be able to assist, or you can build
your own.
Care and Cleaning
Mackie Reference Studio Monitors will provide many
years of reliable service if you follow these guidelines.
• Avoid exposing the monitors to moisture.
• Avoid exposure to extreme cold (below freezing
temperatures).
• Use a dry cloth to clean the cabinets. Only do this when
the power is turned off.
There are several protection mechanisms designed
into the MR8mk2 to safeguard the loudspeakers and
amplifiers from inadvertent damage.
CAUTION: The protection circuits are
designed to prevent damage to the
loudspeakers under reasonable and sensible
conditions. Should you choose to ignore the warning
signs (i.e., excessive distortion), you can still damage
the speakers in the MR8mk2 by overdriving them. Such
damage is beyond the scope of the warranty.
Overexcursion Protection
A 12 dB/octave high-pass filter at 40 Hz just prior to
the low-frequency amplifier prevents very low
frequencies from being amplified. Excessive
low-frequency energy below 40 Hz can damage the
woofer by causing it to “bottom out,” also known as
overexcursion, which is equivalent to a mechanical form
of clipping.
Thermal Protection
All amplifiers produce heat. The MR8mk2 is designed
to be efficient both electrically and thermally.
• If for some reason the heatsink gets too hot, a thermal
switch activates and turns off the amplifier. This
protection operates independently for the
low-frequency and high-frequency amplifiers. Therefore,
it is possible for only the low frequency or high
frequency amplifier to shut down while the other
remains on.
• When the heatsink cools down to a safe temperature,
the thermal switch resets and normal operation
resumes.
• If the heatsink temperature again gets too hot, the
shutdown process repeats. Should this happen, make
sure that airflow to the rear of the cabinet is not
restricted.
Integrated Magnetic Shielding
The MR8mk2 contains drivers with large magnetic
structures. The drivers’ magnets are shielded to help
prevent the magnetic field from radiating out into the
environment and playing havoc with computer monitors
or TV screens. Unshielded speakers can cause
distortion in both the shape and color of the picture
if placed too close to a CRT (cathode ray tube). If you
have a particularly sensitive computer monitor or TV
screen, it may be necessary to move the speakers a few
inches away.