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Protection Circuitry
The DPA-Series power amplifiers are equipped with extensive protection circuitry:
• initial current inrush limiter
• power-on delay
• RF and DC protection
• Back-EMF protection
• limiters for the audio signals
• output peak-current-limiters
• thermal overload of the heat sink
• thermal overload of the mains transformer
• output voltage overload limiters
High-level signals in the low frequency range can drive the output transformers of power amplifiers that
do not provide audio signal limiters into saturation, resulting in nasty distortion and high thermal load of
the power amplification stage. The audio signal limiters of the DPA-Series power amplifiers are designed
to quickly identify the occurring saturation of the core of an output transformer. The level is dynamically
reduced to a value, that stays just below the point of where the saturation starts. The Limit-LEDs on the
front panel indicate that the limiters have been activated. Despite the protection that is provided through
the audio signal limiters, the Limit-LEDs should not light over a longer period of time. Please, locate the
cause of the faulty operation – e. g. lower the LF-EQ setting at the connected mixing console when at the
same time the input level at the power amplifier is approximately +10 dB above the nominal input level.
The DPA-Series power amplifiers employ integrated Lo-Cut filters at 45 Hz with 18 dB/oct. for each
channel. They protect the loudspeaker systems that are connected via output transformers against
low-frequency audio signals, which, depending on the quality and size of the involved transformers, could
lead to problems with core saturation. In addition to the 45 Hz Lo-Cut filters, the frequency response of
the DPA-Series power amplifiers top margin is set by 30 kHz Hi-Cut filters with 12 dB/oct., preventing
unwanted high-frequency audio signals from being present at the outputs.
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