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Protection Circuitry
• The DPA-Series power ampliers 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 ampliers
that do not provide audio signal limiters into saturation, resulting in nasty distortion and high thermal
load of the power amplication stage. The audio signal limiters of the DPA-Series power ampliers
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 connec-
ted mixing console when at the same time the input level at the power amplier is approximately
+10 dB above the nominal input level.
The DPA-Series power ampliers employ integrated Lo-Cut lters 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 lters, the frequency re-
sponse of the DPA-Series power ampliers top margin is set by 30 kHz Hi-Cut lters with 12 dB/oct.,
preventing unwanted high-frequency audio signals from being present at the outputs.