17
If the loudspeaker cable is inadvertently
shorted out, these sorts of currents are quite
capable of causing some cables to catch fire.
We know of one such instance with an
amplifier rated according to the table!
As we do not wish to set your house on fire
we have limited the peak output current to
15 A.
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
•
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 that
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 heat-sink
temperature and calculated average
dissipated power in the transistors. The higher
the heat-sink temperature, and the higher the
mean power dissipated in the output
transistors, the greater this reduction. This will
only occur at very high heat sink temperatures
and very high mean output powers.