Protection Features; Thermal Protection; Short Circuit; Dc Voltage Protection - Crest Audio CPX Series Operating Manual

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Protection Features

The CPX 4 amplifier incorporates several circuits to protect both themselves and loudspeakers under virtually any

situation. Crest 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 Gain Comparator

Limiting

or GCL gain reduction mode, the speaker load remains connected, but clipping percentage is instantly

reduced. DC voltage on the output, excessive subsonic frequencies or thermal overload will cause the channel's

output to disconnect from the speaker load until the problem is corrected or the amplifier cools down.

Gain Comparator Limiting

Any time a channel is driven into hard, continuous clipping, the GCL 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 GCL circuit include uncontrolled feedback,

oscillation, an improper equipment setting or malfunction upstream from the amplifier. Normal program

transients will not trigger the GCL, only steady, excessive clipping will. The GCL LED will flash on peaks when GCL

is active, and will flash brightly with clipping when GCL is disabled.

Internal fans keep the amplifier operating well within its intended temperature range under all normal conditions.

If either channel's heat sink temperature reaches 90°C, both channels of the amplifier will shut down until it has

cooled. During this time, the THERMAL PROTECT LED will light up and the fans will continue to run at high speed.

If an output is shorted, the overcurrent protection circuit will engage and reduce the output of the amplifier to

protect the output devices. Solid red GCL LEDs and dim signal LEDS is an indication of a short circuit and should

be investigated immediately. To find the cause of the overload, start by disconnecting one output at a time, and

then one speaker at a time until the bad cable or damaged speaker is isolated.

If a DC or subsonic voltage is present at the outputs, a crowbar circuit engages to prevent loudspeaker damage.

At power-up, the amplifier stays in mute mode with outputs disconnected for several seconds while the power

supplies charge and stabilize. When power is removed, the mute mode engages so that no thumps or pops are

heard.

(GCL)

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Cpx 4