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28B-SST Amplifier
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FRONT PANEL (refer to illustration above)
13. ‘28B-SST’ power switch
The front panel label ‘28B-sst’, is a push on push off switch used to apply or remove AC line power to the soft start
circuitry. ( Note: the rear circuit breaker must be on for the amplifier to power-up)
14. LED Indicators
The 28B-SST has an LED indicator to monitor the following conditions:
Unlit - indicates the amplifier is turned off.
Red - indicates the amplifier is muted (as in a power-up sequence)
GReen - indicates the amplifier operation is normal.
FlashinG Red - indicates the amplifier clipping.
ORanGe - indicates thermal shutdown.
Power up sequence
After pushing the '28B-SST POWER' switch, the LED will turn from unlit to red (mute). When the power supply has sta-
bilized the amplifier will come out of mute and the LED will change to green (normal operation).
Unlit LED ( power off )
The 28B-SST LED when unlit indicates no A/C mains power is present and the amplifier probably needs only to be
powered on or the rear panel circuit breaker is switched off. Should the amplifier not power on when the power switch is
pushed see the installation instructions.
Clipping ( flashing red )
Clipping occurs when the channel output level no longer can follow the level increase at the input (Over driven input
condition). When the 28B-SST is driven into clipping the LED will change from green to red then back to green when
the level is reduced ( Flashing Red ). Momentary clipping can be tolerated, however it indicates that maximum undis-
torted power has been surpassed and potential speaker damage may result if overload conditions persist. Any amplifier
that is constantly operated into clipping indicates a more powerful amplifier is needed for that application.
Thermal Shutdown ( orange )
The 28B-SST has thermal shutdown circuitry to prevent damage due to overheating. Should thermal shutdown occur,
the amplifier will mute, and the LED will turn orange indicating this condition. When the amplifier has cooled to a safe
operating condition the 28B-SST will return to normal operation. Persistent Thermal shutdown indicates steps need to
be taken to increase airflow across the heat sink. ( Also see installation section on ventilation ).
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