Internal Configuration Switches; Temperature Control - MC2 Audio MC1250 Operating Instructions Manual

The release time can be set to infinity which changes the limiter to function as an AUTOMATIC GAIN
CONTROL. In this mode, if the signal goes above the threshold level, the gain of the amplifier will be
reduced. This reduction will remain until the level controls are manually turned back up, or until the
amplifier is switched off.
NOTE: All levels are referenced to the clipping point of the amplifier and not an actual output
voltage or power level. If the mains power drops or increases then the limit threshold will
also change, thus maintaining maximum output level.

Temperature Control

If the heat sinks get excessively hot, the controller will automatically reduce the supply voltages to the
power devices. This is totally inaudible, it does not effect the levels, but merely reduces the amplifier
headroom by about 1.5dBs. The heat generated by the heat sinks is reduced by 30%. If the amplifier is
still getting too hot there will be a further reduction. If the temperature still continues to rise the
controller will disconnect the outputs. Just before this "shutdown" point, the temperature LED will start
flashing, and it will stay on permanently whilst the amplifier is "shutdown".
The operation of the temperature LED can be changed (see Sw1, internal configuration switches below)
in the alternative position. The LED will come on as soon as the first headroom reduction point is
reached. In certain applications it is important for the user to know this. All other functions remain the
same.
Normal dynamic signals will not cause the amplifier to overheat unless the air filter is clogged or the
ventilation is inadequate. (See installation section.)
Fault Indicators
If the outputs are shorted or if DC is present, the control circuit will disengage the outputs and the fault
LED will illuminate. The controller will keep monitoring the amplifier and will reconnect the outputs and
fade up the signal when the fault is cleared.
The controller also monitors all supply voltages and the mains transformer temperature, any fault with
these will cause the amplifier to shut down and both fault LEDs will show.
2 ohm & Bridged LEDs
These indicate the position of the switches on the rear panel. The 2 ohm LED will also illuminate if the
controller senses a low impedance load (excessive temperature rise).

INTERNAL CONFIGURATION SWITCHES

As these can only be accessed by removing the top panel this should only be carried out by qualified
personnel.
The control PCB is located on the side of the unit behind the front panel. The switches are an 8 switch
DIL package at the rear of the PCB. For full description of the switches consult the Service manual.
The standard configuration is for all switches to be ON, except Sw2 and Sw6, which are normally OFF.
Sw 1 Temp LED operation. ON = Standard position, OFF = alternative position. (See
temperature control section above.)
Sw 2 (Normally OFF) This selects the auto reconnect mode. If switched OFF when a fault has
been detected, the amplifier will not reconnect the outputs even when the fault is cleared.
This is a safety requirement in certain applications.
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