Section 1
DESCRIPTION
1
.1
GENERAL
DC-300A PICTORIAL
The DC-300A is a dual-channel high-power amplifier for
precision amplification of frequencies from DC to
20KHz.
The unit features extremely low harmonic and
intermod-
ulation distortion, very low noise, highest “damping
factor,”
and quality parts and workmanship. Because of
the large output power,
It
is possible to obtain a monaural
70-volt balanced line without using an output transformer.
The DC-300A contains a new CROWN developed Signal
Programmed Automatic Current Executor (SPACE
control) electronic amplifier protection circuit which
manifests no
flyback
pulses, thumps, or shut-down. At
audio frequencies any impedance load including totally
reactive loads may be driven with no adverse effects.
Only maximum output power will be affected by varia-
tions in load impedance. At sub-sonic to DC frequencies
the limiter acts as a VI limiter to provide optimum pro-
tection for the extremely rugged silicon hometaxial
output devices (total of 16 for a total of 2400W dissipation).
A pair of thermal switches remove power from the unit
if overheating occurs due to insufficient ventilation, The
AC line is fused to protect the power supply.
See Section 3.2 for a description of the protective systems.
The power supply features a 1 KW transformer and large
computer-grade filter capacitors giving over 48 joules
of energy storage.
A total of 44 discrete transistors, 1 linear IC (dual op amp),
26 diodes, 1 bridge rectifier, and 3 zener diodes are used in
the
DC-3OOA
circuitry. With the integrated circuit, the
effective number of semiconductors is 60 transistors, 30
diodes, and 3 zener diodes.
The output devices, 8/channel, are conservatively em-
ployed, having a total peak current rating/channel of 120
amps in a circuit that is limited to a maximum of 28
amps. Among its unique features, the circuitry includes
the CROWN-pioneered and patented
AB+B
output con-
figuration.
The input operational amplifiers are powered by two
voltage-regulated supplies. This results in complete
channel-to-channel isolation and independence from line
voltage variations.
Total direct coupling results in perfect, instantaneous,
thump-free overload recovery even on non-symmetrical
waveforms. This cannot be said for any AC-coupled
amplifier presently in existence. Turn-on is instantaneous
with no program delays.
Front-panel controls include two independent heavy-duty
level controls and a power switch with an associated pilot
light. DC balance controls, which never need adjustment
in normal operation, are located behind the front-panel.