Protection Systems - QSC PLX 1804 User Manual

Protection Systems

Both amplifier platforms are fully protected against adverse conditions, but their behavior and user adjustments are different.
PLX 1802/2502/3102/3602 models:
•Clip Limiting may be switched on the rear panel to prevent severe overdrive. This protects speakers and somewhat reduces
the load on the amplifier.
•Internal current limits protect the output transistors against overloading. Peak limiting may occur at full output if using more
than four 8-ohm speakers per channel, or if the speaker wiring is shorted. The red Clip LED will flash brightly, and the ampli-
fier may sound distorted. If the amplifier is driven hard under these conditions, the current limit will be further reduced,
causing an increase in distortion. If the amplifier appears to be losing power during peaks, check the speaker wiring and
number of speakers. Using Clip Limiting will reduce this distortion, but for best results do not exceed the rated loading.
•If the amplifier stops completely for several seconds after a very loud signal, it may be overloading the AC service. This only
occurs if the AC voltage sags more than 30%, and will be more likely if driving many speakers at once. Use short, heavy-
gauge AC cables and do not plug too many amplifiers into a single outlet.
•In Bridge Mono, the amplifier may shut down for several seconds if driven too hard into loads less than the rated 4-ohm
minimum.
•If the amplifier overheats due to prolonged overload or high external temperature, it will mute for about 30 seconds with the
fan running at full speed for maximum cooling. Make sure the rear intake is getting a free flow of cool air.
PLX 1104/1804 models:
•These models have completely automatic internal protection that maintains operation even under extreme conditions.
•Overdrive distortion will cause the red Clip LED to flash. If driven constantly into clipping, internal circuitry smoothly reduces
the volume to minimize distortion and stress.
•These models are rated for 4-ohm loads. Do not use more than two 8-ohm speakers per channel. Using too many speakers
may trigger limiting and cause a loss of volume.
•Internal current limits protect the output transistors against overloading. Moderate overloading will trigger clip limiting, and
smoothly reduce output level to prevent distortion. Severe overloading, such as driving the amplifier hard into a shorted
speaker wire, may cause short, rapid muting. Check the speaker wiring for shorts if the amplifier "chatters".
•Overheating may occur due to prolonged overdrive or high external temperature. This will first trigger thermal limiting,
reducing volume so that the amplifier remains below its thermal limit and keeps running. If input signals are still too high,
the amplifier may eventually mute for about 30 seconds with the fan at full speed for maximum cooling. Make sure the rear
intake is getting a free flow of cool air.
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