Speaker Protection

Thermal Protection

The internal fan(s) will keep the amplifier operating well within its intended temperature range under all normal conditions. If a chan- nel’s heat sink temperature reaches 75°C, (85°C for Models 7001 and 8001) which may indicate an obstructed air supply, clogged air filter, etc., that channel will independently protect itself by disconnecting its load and shutting down until it has cooled to 72°C ( 82°C for Models 7001 and 8001). During this time, the channel’s DC/Temp LED will light. If the power transformer gets too hot, its ther- mal sensing circuit will disconnect both channel outputs. Normal operation will resume automatically once the transformer cools to a safe level. During this time, the Active LED will extinguish, the Temp/DC and Clip/Limit LED’s will stay lit, and the cooling fan will stay running.

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 overcurrent 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 at its output terminals, its output relay will immediately open to prevent loudspeaker dam- age. The channel’s Temp/DC LED will light.

Subsonic Frequencies

The Professional Series amplifiers have built-in 12 dB per octave high-pass filtering, cornered at 8 Hz, to provide subsonic frequency protection for each channel. In addition, a channel’s output relay will open if excessive subsonic energy appears at the output.

Turn-On/Turn-Off Protection

At power-up, the amplifier stays in the protect mode, with outputs disconnected, for about 3 seconds while the power supplies charge and stabilize. While the output relays are open, the Temp/DC LED’s light. When power is removed, the speaker loads immediately dis- connect so that no thumps or pops are heard.

AutoRamp Signal Control

Whenever a Professional Series amplifier powers up or comes out of a protect mode, the AutoRamp circuit activates. While the speak- ers are disconnected, the AutoRamp circuit fully attenuates the signal. After the output relay closes, the signal slowly and gradually raises up to its set level. The AutoRamp Signal Control circuit has some important advantages over the conventional instant-on circuits:

1.If a signal is present during power-up (or when coming out of protect), the speakers are spared a sudden, potentially damaging burst of audio power.

2.Because the gain is reduced until after the output relay closes, no arcing occurs at the contacts, thereby extending their useful life.

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Crest Audio Pro Series Power Amplifiers