MACKIE MR5 - Manual (Page 8)

8
MR5
MR5
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
MR5.
• 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!
You can purchase quality cables from your Mackie
dealer.
• In certain home theater applications, it may be necessary
to connect the speaker outputs from a stereo receiver
to the inputs of the MR5, 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 MR5! Speaker levels are much
higher than line levels and can damage
the input circuitry in the MR5.
You can, however, insert a speaker-level to line-level
signal attenuator between the receiver’s speaker output
and the MR5’s input. Your Mackie dealer may be able to
help you find one, or you can build your own.
CARE AND CLEANING
Your Mackie Reference Studio Monitors will provide
many years of reliable service if you follow these guide-
lines.
• Avoid exposing the monitors to moisture.
• Avoid exposure to extreme cold (below freezing tem-
peratures).
• 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 MR5 to safeguard the loudspeakers and ampli-
fiers 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 MR5 by overdriving them. Such damage
is beyond the scope of the warranty.
Overexcursion Protection
A 12 dB/octave high-pass filter at 60 Hz just prior to
the low-frequency amplifier prevents very low frequen-
cies from being amplified. Excessive low-frequency
energy below 60 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 MR5 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 protec-
tion 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 re-
sumes.
• If the heatsink temperature again gets too hot, the shut-
down process repeats. Should this happen, make sure
that airflow to the rear of the cabinet is not restricted. If
the ambient air temperature is very warm, try pointing
a small fan toward the heatsink to increase the airflow
through the ventilation holes.
Integrated Magnetic Shielding
The MR5 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 particu-
larly sensitive computer monitor or TV screen, it may be
necessary to move the speakers a few inches away.