Crest Audio PRO 200 SERIES, Руководство пользователя

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Safety
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Protection Features
Pro 200 Series amplifiers incorporate several circuits to protect both themselves and
loudspeakers. 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 ACL gain reduction mode, the speaker load will remain
connected but clipping percentage or output power will be instantly reduced. When a
problem occurs that causes a channel to go into a protection mode, the Temp LED or
DC LED for that channel will glow. DC voltage on the output, excessive subsonic fre-
quencies or thermal overload will cause the channel’s output relay to open, disconnect-
ing the speaker load until the condition is corrected.
Automatic Clip Limiting (ACL)
Any time a channel is driven into hard,continuous clipping,the clip limiter circuit will auto-
matically reduce the channel gain to a level just slightly into clipping, which protects the
speakers against the damaging, high power, continuous square waves. Situations that may
activate the clip limiter include uncontrolled feedback, oscillations, and improper equip-
ment setting or a 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
Pro 200 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 out-
put stage protection is far superior to the 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 normal conditions. If a channel’s heat sink temperature reaches 75°C (which
may indicate an obstructed air supply),that channel will independently protect itself by dis-
connecting its load and shutting down until it has cooled. During this time, the channel’s
Temp LED will light, the Active LED will extinguish and the cooling fans will run at their
highest speed.
Short Circuit
If an output is shorted, the IGM and thermal circuits will automatically protect the ampli-
fier. 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 discon-
necting the load.
DC Voltage Protection
If an amplifier channel detects DC voltage or subsonic frequencies at a channel output,
the respective output relay will immediately open to prevent loudspeaker damage.The
channel’s DC LED will light.