6.5.5 High-impedance warning (open load)
A high-impedance (open load) condition is indicated
when an input signal above approximately -29 dB
is detected and no functioning loudspeakers are
connected to the amplifier. The fault in indicated
by a orange 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 -29 dB, it might cause the
indicator to first turn green, and then red,
even in situations where no speaker is connected.
6
.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 (-4 dB 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 orange 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 -4 dB 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.
6
.5.7 Temperature protection
Thermal measurement points are provided on each
output channel as well as on the power supply. These
indicators will, if the pre-specified temperature level
is exceeded, give a high temperature warning. This
warning condition is indicated by a flashing TEM LED
on the front panel.
As the amplifier approaches a thermal protection
threshold, the warning LED sequence will start with
short on-time bursts. If the amplifier continues
to overheat and approaches the temperature limit,
the flashing sequence will be defined by longer and
“
”
longer on-time bursts until the protection mode is
activated.
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.
6
.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
.
6
.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
MM Series amplifiers. The MM Series amplifiers
have very low inrush power as the capacitors are
charged slowly and in a controlled manner ensuring
that breakers will not trip.
Several amplifiers will, under normal conditions, be
able to be powered up simultaneously.
NOTE
NOTE
20
MM Series Operation Manual
