Crest Audio Stereo Amplifier - Manual (Page 16)

Page 14 Crest Audio Pro Series Power Amplifiers
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.
Speaker Protection