Protections | 13
∞
12 : 2.4. Total power limiter
When the module detects a long term output current of
>11 A, and an output power grater than 700 W, it will limit the
output power accordingly.
12 : 3.Amplifier protections
Amplifier protections are triggered by the audio signals,
output currents and voltages, and by the temperature of
the output stage’s devices. Temperature is read by NTC
(Negative Temperature Coefficient) thermistors. NTCs
provide a voltage proportional to temperature read, which
decreases with an increasing temperature.
The average of the temperatures read by all NTCs
triggers a secondary thermal limiter which acts as follow:
0dB @ 70°C, and -20dB @ 85°C. When temperature exceeds
the safety threshold of 85°C the system switches off.
displays the relationship between temperature
and voltage drop across NTC thermistors. NTC’s voltage
drop for each channel are routed to the respective
TEMPMON contacts (pin #12 and #23) on PL1001.
The limiting factor is 0dB @ 85° C, and -20dB @ 95° C.
Since the temperature is detected on the PCB surface
it does not represent the actual temperature of the plate:
be aware that some parts of the amplifier may be at higher
temperature, but not at risk of failure.
12 : 3.1. Harmful signal protections
Bad signals can cause amplifier and loudspeakers
damages. In order to limit such failures, harmful signal
triggers specific protections.
12 : 3.1.1. Output short circuit
If the load impedance is too low or the loudspeaker
cable is short circuited (because of voice coil damages,
wires short circuit, improper wiring, etc), the amplifier output
current could rise to harmful values.
When the output current reaches 31 A
peak
the amplifier
section switches off (in less than 5us), while the power
supply is still working.
The module will then start a series of checks at different
intervals, in which it will try to switch itself on again, as
described in the table below, and will then cycle the entire
process indefinitely.
Time
Cycle #
2 s
30 times
10 s
90 times
5 min
6 times
30 min
1 time
12 : 3.1.2. RMS output current protection
Two RMS output current protections are available:
short-term current limiter and long-term current limiter with
dedicated thresholds and attack times.
12 : 3.1.3. High frequency stationary loud signals
High frequency stationary signals, such as sine waves
with high amplitude, tend to stress the amplifier section of
the module as well as the loudspeakers voice coils.
If the output signal is above 20 kHz the protection will
activate in 0.5 s when the output amplitude exceeds 20 V
RMS
.
f
High Freq. limiter
THR= 20Vrms @20kHz, ATK= 0.5s
12 : 3.1.4. Soft Clip Limiter
Clipping signals will be smoothed out with an attack
time of 2 ms and a release time of 20ms.
12 : 3.1.5. Output Current Mismatch Protection
When using the module in PTL mode, there is a risk of
encoutering current mismatch between the paralleled chan-
nels. A protection will intervene and mute the outputs for
60 seconds. The module then restarts normally unless the
protection intervenes again.
In order to avoid this protection verify that the PTL out-
put cable is made of short cables that are also the same
lenght between each other.
0
-10
-20
0
65
85
95
-30
o
C
dB
-∞
Gain Reduction
Safety
Shutdown
Output stage
temperature limiter
NO
YES
