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PowerH SERIES
34 Owner’s Manual
reduced. As soon as the power amp’s temperature returns to a non-critical state, the ATP system
imperceptibly switches back to full supply voltage.
Thermal Limiter is the second measure that is only activated if, under extreme conditions, Voltage
Limitation is not sufficient. The thermal limiter circuit unobtrusively reduces the amplification of the power
amplifier. Only if even this measure does not re-establish thermal balance, the ATP system activates
Thermal Mute as the last step to completely switch off the signal path.
This step-by-step functioning of Advanced Thermal Protection enables PowerH SERIES amplifiers
to still be in operation under conditions where various other amps would have ceased operation.
The PROTECT-LED lights immediately to signal any direct intervention in the signal path by limiters and a
corresponding indicator in IRIS-Net™ allows the FOH-engineer to react instantly, even before interference
with the audio performance becomes noticeable.
Monitoring Ambient Temperature
PowerH SERIES amplifiers constantly monitor the temperature of several active electrical
components during operation. In addition, monitoring also includes the temperature of the inlet cooling air
and as a result also the temperature of the power amp’s ambience. If, for any reason the ventilation
louvers are totally blocked or the inlet outer air exceeds the upper temperature limit for effective cooling,
this would inevitably lead to overheating of the power amplifier. This condition can possibly occur even
when the power amplifier is in idling mode, for example when it is installed in a closed rack case.
However, during idling the preventive measures of the Advanced Thermal Protection (see previous
paragraph) show hardly any impact. For this reason the power amplifier enters standby mode once it is
operated under extreme thermal load, which is caused by inadequate cooling. In that case, PROTECT-
LED and STANDBY-LED blink alternately.
The power amplifier automatically re-starts after approximately 20 minutes. As an alternative, re-starting
the power amplifier manually using the mains switch or via IRIS-Net™ is also possible, if the device has
cooled down sufficiently.
HF-Limiter
If the power amplifier processes high-frequency signals at high levels, amplification is automatically
reduced after a while to protect the output stages against damage. Most of the time such conditions result
from a malfunction in one of the devices that are connected upstream in the signal chain. The situation
becomes particularly critical for power amplifier and connected tweeter cabinets when the signal is still in
the audible range or just above the auditory threshold. Conventional HF-Protection circuits are not
sensitive enough to react within this particular range, since they are primarily targeted at detecting fault
conditions of the power amplifier itself.
Next to conventional HF-Protection, PowerH SERIES amplifiers have also a HF-Limiter, which is
frequency-dependent and permanently monitors the output signal. The HF-Limiter possesses the ability to
reliably differentiate between normal reproduction of music and speech and critical operating conditions.
The power amp’s signal amplification is automatically reduced whenever such a critical operating condition
occurs.