L-ACOUSTICS LA15a 115V Manual V1.0 27/01/2003
19
The
“CLIP”
LED indicates when the amplifier output is clipping or limiting. It has two different indication
statuses:
•
If the clip limiter is engaged the CLIP LED has a short time constant and illuminates briefly.
•
If the clip limiter is not engaged the CLIP LED has an increased time constant and illuminates for a
longer period.
The remaining PROTECT LEDs indicate if any protection circuits are activated. Protection features are
described in the following section.
8. PROTECTION FEATURES
Each L-ACOUSTICS amplifier has many advanced protection features, protecting both the amplifier and
the loudspeakers connected to it should a fault condition arise. Under normal use these features are
inaudible. All protection circuits are independent.
8.1 CLIP LIMITER
The clip limiter prevents dangerous clipped signals from reaching the loudspeaker and causing damaging.
When an amplifier is severely overdriven, the output waveform is clipped (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 clip 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. Once the amplifier comes out of a protect
condition, the output level has a slow rise time - the effect is like turning the gain up slowly. Note: if the
signal is distorted or clipped before it reaches the amplifier, the clip limiter cannot detect it and will not
be activated.
Under normal operation, clip limiting is inaudible. The limiter can be turned On or Off by depressing or
pressing the relevant rear panel clip limit switch. L-ACOUSTICS
recommends leaving the clip limiters
switched ON at all times (Channel A, B rear panel clip limiter buttons depressed in the “IN” position).
8.2 THERMAL PROTECTION
If the amplifier is driven hard into a low impedance load, the cooling fans will run at high speed. If this
condition persists, 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
®
heat sink reaches a temperature above 90
0
C.
8.3 VHF PROTECTION
If a signal above 12 kHz is detected at the amplifier outputs for more than five seconds at full output
power, VHF protection mutes the input signal. This is indicated on the front panel LED 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.
8.4 SHORT CIRCUIT PROTECTION
All L-ACOUSTICS amplifiers are completely short circuit-protected. Short circuit protection circuitry
permits very high peak currents, but still holds the output devices within the safe operation area. If a
short circuit condition is maintained, the affected channel will eventually go into thermal protect cycle
until the short circuit has been removed.
