Crest Audio CC 5500, Owner'S Manual

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p.
10
CC
TM
owner’s manual
protection features 5
CC Series amplifiers incorporate several circuits to protect both themselves and loudspeakers
under virtually any situation. Crest Audio has attempted to make the amplifiers as foolproof as
possible by making them immune to short and open circuits, mismatched loads, DC voltage, and
overheating. If a channel goes into the Automatic Clip Limiting or ACL
™
gain reduction mode, the
speaker load remains connected, but clipping percentage or output power are instantly reduced.
When a problem occurs that causes a channel to go into a protection mode, the Temp LED for
that channel will glow. DC voltage on the output, excessive subsonic frequencies, or thermal
overload will cause the channel’s output relay to disconnect the speaker load until the problem is
corrected or the amplifier cools down.
automatic clip limiting (ACL)
Any time a channel is driven into hard, continuous clipping, the clip limiter circuit will
automatically reduce the channel gain to a level just slightly into clipping, guarding the speakers
against the damaging high power continuous square waves that may be produced. Situations
that may activate the clip limiter include uncontrolled feedback, oscillation, or an improper
equipment setting or malfunction upstream from the amplifier. Normal program transients will
not trigger the clip limiter; only steady, excessive clipping will. The ACL LED will glow brightly
and continuously when limiting occurs.
IGM
™
impedance sensing
CC Series amplifiers feature innovative circuitry that allows safe operation into any load.
When an amplifier sees a load that overstresses the output stage, the Instantaneous Gain
Modulation (IGM) circuit adjusts the channel gain to a safe level. This method of output stage
protection is far superior to conventional, brute force type limiting found on other amplifiers.
The IGM circuit is sonically transparent in normal use and unobtrusive when activated.
thermal protection
The internal fans will keep the amplifier operating well within its intended temperature range
under all normal conditions. If a channel’s heat sink temperature reaches 75°C, which may
indicate an obstructed air supply, that channel will protect itself independently by disconnect-
ing its load and shutting down until it has cooled. During this time, the channel’s Temp LED
will glow, the Active LED will go out, the ACL LEDs will stay lit and the cooling fans will run
at high speed. The CC 1800 utilizes one common heat sink and single fan, but retains the
separate circuitry.
short circuit
If an output is shorted, the IGM and thermal circuits will automatically protect the amplifier. The
IGM circuit senses the short circuit as an extremely stressful load condition and attenuates the
signal, protecting the channel’s output transistors from over current stress. If the short circuit
remains, the channel will eventually thermally protect itself by disconnecting the load.
DC voltage protection
If an amplifier channel detects DC voltage or subsonic frequencies at its output terminals, its
output relay will immediately open to prevent loudspeaker damage.