Halcro DM38 Owner's Manual page 11

dm38
One also has to question the belief that an amplifier should be capable of such
unreasonably high output currents. Consider the following facts:
Most loudspeakers have impedances of 4 ohms (not 1 or 2 ohms).
All valve amplifiers are output current limited, and yet the industry does not
consider this a problem, which is inconsistent with the belief that maximum
available current limiting is a problem.
All well designed loudspeakers have impedances that do not deviate excessively
from their nominal impedances and hence no excessively high currents are
required anyway.
If indeed a 4 or 8 ohm loudspeaker does have an impedance of 1 ohm at a
particular frequency, one must wonder where the heat generated is dissipated if
this load is predominantly resistive or why the coupling is so poor if this load is
predominantly reactive.
Hence we believe that these excessively high output currents are,
not required for well designed loudspeakers, and
highly dangerous.
Many people have listened to maximum available current limited amplifiers played
through different loudspeakers without encountering any current limiting problems
that is, obvious "cracking" sounds at very loud listening levels, except for loudspeaker
or voltage overloads which are independent of current limiting.
Output transistor protection
Halcro uniquely incorporates circuitry which accurately calculates the mean power
dissipated in the power output transistors (power FETs). Another calculating circuit
then may reduce the maximum available output current according to the heatsink
temperature and calculated average dissipated power in the transistors. The higher the
heatsink temperature, and the higher the mean power dissipated in the output
transistors, the greater this reduction. This will only occur at very high heatsink
temperatures and very high mean output powers.
TM
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