Marantz PROFESSIONAL Series - Circuit Description

CIRCUIT DESCRIPTION
GENERAL
The 510 Series consist of the Models 510 and
510M. Both amplifiers use identical output
amplifier stages and have the same output capa-
bilities. The 510 is different only in that the VU
meter and its circuitry have been eliminated.
AC power is applied through a line fuse and
power switch to the soft start circuit which limits
the peak AC line inrush current to 12 Amps peak
(120 Volt version). A relay K1 is activated and
switches out a limiting resistor R3 when the filter
capacitors C3 and C4 approach full charge. The
power transformer utilized has a highly efficient
thermal conduction to remove heat from the
transformer core. A full wave high current bridge
rectifier CR1, supplies the DC potentials to two
10,000 microfarad storage capacitors C3 and C4
having a total stored charge energy of 74 joules,
providing the high reserve necessary for high level
program demands.
The input signal is applied to the variable gain
control, which is buffered from the differential
input amplifier by a unity gain dual feedback pair
complementary amplifier, Q301 and Q302. The
differential input amplifier, Q304 and Q306,
receives both negative AC and DC feedback from
the output of the power amplifier. The 100 per
cent DC feedback, through differential compar-
ison, provides precise control of the zero DC off-
set voltage at the speaker terminals. The TIME
DELAY CIRCUIT at 0303 delays turn-on of the
differential current source, Q305, for a period of
three to five seconds.
Q307 and Q308 serve as unity gain differential
buffer amplifiers, to prevent loading of the input
differential amplifier Q304 and Q306 and to
provide a low impedance voltage drive to the
complementary current source drive transistors,
Q309 and 0310. Note that a symmetrical drive
signal is produced by an active bi-directional
complementary symmetry circuit technique. This
results in a completely symmetrical positive and
negative drive swing with equal low and high
frequency characteristics.
The bias network at Q401 establishes an accurately
regulated and temperature controlled bias source
for the output devices via the pre-driver transistors
0313 and Q314.
The drive signal from Q309 and 0310 is passed to
the complementary pre-drivers Q313 and 0314.
These devices, connected as emitter followers,
provide a medium impedance drive source for the
master drivers, O403 and 0404, in the Marantz
“Power Stack’’ configuration.
The “Power Stack” is a series parallel connection
of eight power output devices in each channel,
operating in push pull. The output devices
consist of positive NPN paralleled pairs 0406,
Q410, and 0407, 0411 and negative PNP parallel-
ed pairs, Q408, 0412, and 0409, 0413. The
lower positive and negative paralleled pairs, 0407,
Q411 and 0408, 0412 are driven in a Darlington
connection from master drivers Q403 and 0404
respectively. The upper paralleled pairs, Q406,
Q410 and 0409, 0413 are driven by the positive
and negative slave drivers, Q402 and Q405,
respectively, 0402 and 0405 are biased and driven
by precision metal film resistors in a less than
unity gain positive feedback connection from the
amplifier center point.
The current sensing resistors R361 and R362 and
the protection logic system provide the 5 milli-
second delayed load line limiting protection sig-
nals that drive the protection transistors Q311
and Q312. The protection transistors, in turn,
clamp the drive to the bases of 0313 and 0314
pre-driver transistors whenever long term overload
signals are encountered that would exceed the safe
operating area of the output transistors.
The output signal is monitored by both the
output meters M1 and M2 and the peak overload
flasher while simultaneously being applied tnrough
the thermostatically activated cut-off switch to
the speaker terminals.
The METERS are driven via a precision attenuator
and full bridge rectifier system.
The PEAK OVERLOAD FLASHER circuit re-
ceives sensing signals from the amplifier Output
and the protection circuits. The amplifier peak
output voltage is compared with the power supply
voltage at Q205. The voltage and current signal
from the protection circuit is amplified by Q201
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