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If the amplifier is driven very hard into a low impedance load, the cooling fans will run at high speed. If
the causing conditions continue, the Temperature indicator(s) will illuminate indicating that the amplifier
is about to go into thermal shutdown.
After five seconds the amplifier will go into thermal protection by muting the input signal. After 15-20
seconds the amplifier will have cooled down enough for the amplifier to come out of shutdown and
operate as normal. If the load conditions remain unchanged the thermal protection will be reinitiated.
Thermal protection starts when the I
ntercooler
®
heatsink reaches a temperature above 90
0
C.
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If a signal above 12kHz is detected at the amplifier outputs for more than five seconds at full output
power, the VHF protection mutes the input signal. (This is indicated on the front panel (
2
) labeled
Protect). After five seconds the outputs will un-mute and return to normal operation, unless the output
signal has remained unchanged, in which case the VHF protection will re-initiate.
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All Lab.gruppen amplifiers are completely short circuit protected. The protection circuit permits very
high peak currents, but still holds the output devices within the safe operation area. If a short circuit is
maintained, the channel affected will eventually go into thermal protect cycle until the short circuit has
been removed.
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If the AC mains voltage is over the allowed operational voltage, the power supply will automatically
shut down. Once the mains voltage is above the minimum start voltage and below its maximum
operating voltage the amplifier will restart.
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There are two types of DC protection:
•
Fuses on the supply branches of each channel.
•
A DC crowbar protection that shorts the output if more than 10 volts DC are being detected on the
outputs.
Either of these protections comes into effect once DC voltage is being detected, independently for both
channels.
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