Front Panel - Mackie HR824 Service Manual

FRONT PANEL DESCRIPTION
ON/OFF SWITCH
• Use this switch to turn on or off the HR824
from the front. It works with the POWER
MODE switch on the rear panel in the
following way:
• If the rear POWER MODE switch is OFF, the
front panel ON/OFF switch has no effect.
The PWR LED remains off, so there.
• If the rear POWER MODE switch is ON, the
front panel ON/OFF switch turns the HR824
on and off, as indicated by the PWR LED.
• If the rear POWER MODE switch in the AUTO
ON position, the front panel ON/OFF
switch turns the HR824 on and off as long
as there is a signal present.
OL (overload) LED
• This LED blinks when the amplifiers begin to
clip, and lights steadily if the overload
protection circuit has been triggered.
• Occasional blinking of the OL LED
indicates that the loudest transients are
reaching the maximum output capability
of the amplifiers.
• Frequent or continuous blinking of the OL
LED indicates that you have exceeded the
maximum output capability of the
amplifiers and that the amplifiers are
clipping. If you persist, the overload
protection circuit takes over, reducing the
input level. You should reduce the level
from your signal source until the OL LED
blinks occasionally or not at all.
OVERLOAD PROTECTION
• The high and low frequency power
amplifiers have clipping detectors that
light the OL LED when either power
amplifier output clips.
• If frequent clipping occurs, the driver
thermal overload protection activates a
compressor that reduces the input level to
the amplifiers. During this time the OL LED
lights continuously.
• The compressor was designed to protect
the speakers and its action is highly
audible.
• When listening at a very high volume, you
may find that the OL LED lights frequently.
Since the majority of the power
requirements in any monitor are the low
frequencies, selectively reducing the low
end can provide a little more headroom
and volume for the monitors. Change the
LOW FREQ switch to 47Hz or 80Hz, if
necessary, to reduce the bass response. This
may allow the HR824s to play louder and
eliminate most amplifier clipping.
THERMAL PROTECTION
• The HR824 is designed to be efficient both
electrically and thermally.
• If the heatsinks get too hot, a thermal
switch activates, placing the HR824 into
Standby mode (indicated when the red
PWR LED turns off).
• Should this happen, make sure that airflow
to the rear of the cabinet is not restricted.
• When the heatsinks cool down to a safe
temperature, the switch resets and normal
operation resumes.
• If your service customer complains that
their HR824s keep thermalling out, make
sure they keep them in the vertical position
for improved ventilation. Also make sure
the bias has been set correctly.
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