Lab.gruppen fP2600 - Manual (Page 16)

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Each Lab.gruppen amplifier has many advanced protection features. Should a fault condition arise they are
protecting both, the amplifier and the speakers connected to it. Under normal use these features are
inaudible. All protection circuits work independent from each other.
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The clip limiter is included to prevent from dangerous clipped signals reaching the speaker and damaging
it. If an amplifier is severely overdriven, its output waveform is clipped (its peaks are squared off) –
reducing the crest factor. In extreme cases the waveform can approach that of a square wave. An amplifier
is normally capable of producing far more power under these conditions than its normal undistorted rated
output power.
The limiter works by monitoring the output and comparing the distortion produced between the input and
output of the amplifier. If the distortion exceeds 1% THD for any reason (voltage or current clipping), the
limiter reduces the input signal proportionally. Note that, if the signal is distorted or clipped before it
reaches the amplifier, the clip limiter cannot detect it, and will not be activated.
During normal operation the clip limiting is inaudible. The limiter can be turned on or off by using the
relevant clip limit switch. Note that in Bridge mode the limiters of both channels should be in the same
position, either on or off.
Some manufacturers of loudspeaker controllers do not recommend the use of clip limiters in amplifiers, as
they tend to upset the tracking of the controller’s limiters.
Apart from this single exception, Lab.gruppen recommend to leave the clip limiters switched "on" (button
depressed). As a side-effect, once the amplifier comes out of a protect condition, the output level has a
slow rise time – the effect is like turning up the gain slowly.
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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 “Temp” temperature indicator(s) will illuminate indicating that the
amplifier is about to go into thermal shutdown.
After approximately five seconds the amplifier will go into thermal protection by muting the input signal.
After another 15-20 seconds the amplifier should 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 accordingly. Thermal protection starts, if the Intercooler
® heatsink reaches a temperature
above 90 ° 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 by the LED’s on the front panel
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 circuitry permits very
high peak currents, but still holds the output devices within the safe operation levels. If a short circuit
remains to be present, the channel effected will eventually go into thermal protect cycle until the short
circuit has been removed.
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If the AC mains voltage is lower or higher than the allowed operational voltage (over- or under-
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.
It takes a couple of seconds to self-check (this is known as the "soft start" or "slow start" sequence), the
gain will slowly and gradually be increased back to the previously set level, and the fans will first blow at
high speed before going into "idle". The two green ”ON” LED’s indicate that the power supply is
operating properly.
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