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7.5.5 High impedance warning (open load)
A high-impedance (open load) condition is indicated
when an input signal above approximately -29dB is
detected and no functioning loudspeakers are
connected to the amplifier. The fault in indicated by
a red Sig/Hi-imp LED. The indicator is green when a
valid load is present under the same input signal
conditions.
- Since the Hi - impedance detection initially triggers
only when the input signal rises above -29dB, it
might cause the indicator to first turn green, and
then red, even in situations where no speaker is
connected.
7.5.6 Low impedance protection warning
A low impedance or short circuit fault is detected
when current draw is high (Current Peak Limiter
active) and when, simultaneously, output signal is
low (-4dB LED does not illuminate). When this
occurs, the amplifier protects the output stage from
damage by muting the output signal and bypassing
the circuits. Indication of this fault is a constant red
illumination of the Current Peak Limiter (CPL) LED on
the front panel. The protection will sequence at 6
second intervals to re-measure conditions. If the low-
impedance fault is no longer detected, the amplifier
will un-mute.
- If the CPL turns constant orange, the output is
muted, and the -4dB signal LED is ON, then the
amplifier has gone into maximum current protection.
This situation is caused by an excessive input signal
and is not due to a short circuit. Turn down the input
signal to avoid or remedy this situation.
7.5.7 Temperature protection
If the temperature becomes too high to continue
safe operation, the overheated output channel(s) will
be muted until the temperature returns to an
acceptable level.
Fully active temperature protection (with muting) is
indicated by a constantly illuminated TEM LED.
Temperature measurements will continue at 6
second intervals. The output will un-mute when the
channel or power supply returns to a safe operating
temperature.
7.5.8 Power Average Limiter (PAL)
The Power Average Limiter (PAL) controls the
current-drawing relationship between the power
supply and the mains inlet. PAL limits the maximum
average power consumption according to the power
supply capabilities, ensuring that the PSU will not
overload. In addition, in the larger models that
potentially could pull more current from the mains
than the mains fuses are specified to handle (more
than 16 A), PAL limits the amplifier's maximum
current draw to prevent blowing the mains fuse.
7.5.9 Soft Start
High-powered amplifiers with inadequate inrush
limiting can pull considerable current from the mains
at turn-on. This can result in tripping of fast- acting
mains breakers. Such is not the case with 10K4
amplifiers. The 10K4 amplifiers have very low inrush
power as the capacitors are charged slowly and in a
controlled manner ensuring that breakers will not
trip.
Zenith 10K4 Amplifier Manual
22
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