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Marantz SM-8 - Page 5

Marantz SM-8
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@
Class
A
—
Class
AB
automatic
switching
circuit
3.
P.W
BOARDS
Quarter
A
allows
the
main
amplifier
to
operate
as
a
pure
class
A
amplifier
for
outputs
of
up
to
30W,
which
is
a
quarter
of
the
rated
output
120W
at
8Q,
at
the
switch
to
class
AB
for
outputs
larger
than
30W.
The
transition
from
class
A
to
class
AB
or
vice
versa
is
carried
out
by
switching
the
bias
current
and
the
power
supply
voltage.
As
can
be
seen
from
the
circuit
diagram
the
chassis
of
Mode
Sm-8
consists
of
the
following
units.
Each
unit
mounted
or
a
printed
circuit
board
is
descrided
within
the
square
enclosed
by
a
bold
dotted
line
on
the
circuit
diagram.
The
automatic
switching
circuit
monitors
the
input
volt-
1.
PowerAmp.
.......
mounted
on
P.W.
Board
P60C
age
of
the
main
amplifier
and
the
output
current
of
the
2.
Voltage
Amp.
.....-
mounted
on
P.W.
Board
P70C
speaker
in
order
to
detect
output
transitions.
Note
that
3.
Test
Point.........
mounted
on
P.W.
Board
PJOC
the
use
of
a
phase
correction
circuit
inside
the
detector
4.
A-B
Power
Switch.
..
.
mounted
on
P.W.
Board
PKOC
prevents
waveforms
including
those
with
a
steep
rising
5.
A-B
Detector.......
mounted
on
P.W.
Board
PLOC
edge
from
being
distorted.
The
automatic
switching
6.
ASO
Protector
......
mounted
on
P.W.
Board
PNOC
circuit
can
be
easily
used
for
amplifier
configurations
7.
Connection
........
mounted
on
P.W.
Board
PPOC
uniquely
designed
by
Marantz
by
merely
connecting
the
8.
Speaker
&
input
of
the
detector
to
the
signal
system.
Meter
Switch
.......
mounted
on
P.W.
Board
PSOC
9.
Output
Network.....
mounted
on
P.W.
Board
PWOC
10.
Meter
&
Supply
.....
mounted
on
P.W.
Board
PXOC
@
Large-sized
peak
power
meter
of
the
logarithmic
com-
pressed
type
Large-sized
power
meters
that
are
suitable
for
high
quality
power
amplifiers
are
available.
This
power
meter
can
be
used
to
check
the
output
level
and
the
balance
between
the
right
and
left
channels.
It
operates
by
detecting
signal
peaks,
but
it
displays
rms
values
which
directly
represent
the
outputs
of
the
amplifier
to
an
8Q
load.
In
addition,
since
a
circuit
generating
logarithmic
com-
pressed
displayes
is
used,
outputs
of
small
to
large
quantities
can
be
monitored
without
changing
the
range.
This
power
meter
can
also
be
used
as a
peak
holder
by
setting
appropriate
switches
on
the
panel.
@
Protective
circuit
which
does
not
degrade
tone
quality
The
overload
protective
circuit
detects
both
overvoltage
and
overcurrent
conditions,
while
in
the
area
of
safe
operation
(A.S.O.)
does
not
degrade
the
operation
of
the
drive
transistors.
The
protective
circuit
has
adaptable
characteristics
so
that
its
operation
does
not
interfere
with
the
program
and
its
operation
is
always
constant.
e
Plus
The
power
output
circuit
is
equipped
with
high
efficiency
heat
sinks
to
cool
the
power
transistors,
thus
providing
continuous
high
output
power.

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