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advanced Technology Design Series 1V from
AB International is a modular system of high
performance power ampliﬁers and electronic sig-
nal processing that may be precisely tailored to
the speciﬁc requirements of professional loud-
speaker components. The experience gained from
building three generations of signal-processing
power ampliﬁers brings new features and new
standards of performance to ATD IV.
The AB International ATD Series 644A is a four
channel power ampliﬁer. This compact (three
rack unit) instrument features individual channel
Dip switch level controls and signal/clip indica-
tors, XLR inputs (balanced), and a ground lift
switch, The 644A delivers 270 Watts per channel
8 Ohm, 425 Watts per channel into 4 Ohm, and
290 Watts into 2 Ohm.
The 644A employs only ZOdB of negative feed-
back to reduce forward tran sfer distortion compo
nents to minimum levels. Vl energy limiters are
incorporated for short- circuit protection and a
thermal sensor prevents an over-temperature conr
Other features include convection cooling with):
massive heatsink array and a temperature activatec
DC fan for extreme load conditions, " Soft Clip'
speaker protection circuitry, selectable input sensi
tivity, ground lift switch and a fully modular con
struction for service accessibility.
The AB International Model 644A features de
layed-ON , instant-OFF muting control circuit al
lows supply voltages to stabilize before loudspeak
ers are connected. Speaker connections are in
stantl y removed , should there be an interruption 0
For users desiring speciﬁc non-smndard feature
and/or signal processing , a wide variety of option
are available, including high pass frequencies ,cross
over frequencies and ﬁlter topology and HF powe
response equalization , contact AB Internationa
The 644A operates from 10()»240V 50-60Hz AC
mains and measures 5 1/4 " high (three rack unit)
19" wide and 12.0" deep.