Marantz 3800 - Page 12

jacks.
The
power
amplifier
signal
is
also
applied
to
the
MAIN
and/or
REMOTE
SPEAKER
Terminals
by
the
corresponding
SPEAKERS
Switch.
D.PHONO/MIC
AMPLIFIER
The
low-level
Phono/Mic
Amplifier
consists
primarily
of
a
differential-input
transistor
pair
(0201
and
Q203),
an
emitter-follower
buffer
stage
(0205),
a
high-gain
stage
(Q207),
and
an
emitter-follower
output
stage
(0209).
A
neg-
ative-feedback
network
sets
the
closed-loop
gain
of
this
operational
amplifier
at
40dB
and
establishes
the
proper
high-frequency
roll-off
points.
Other
components
in
the
feedback
network
provide
precise
Mic
and
Phono
(RIAA)
equalization.
<A
one-millivolt
input
signal
is
nominally
increased
to
100
millivolts
through
the
Phono/Mic
Amplifier.
E.
DOLBY
ENCODE/DECODE
PROCESSORS
With
the
DOLBY
Switch
set
to
REC
I,
the
DOLBY
Encoder/Decoder
(U501)
functions
as
an
encoder
and
increases
the
amplitude
of
low-level,
high-frequency
signals
10
dB.
Spec-
cifically,
portions
of
the
incoming
signal
are
applied
to
a
level-
and
frequency-sensitive
"“sidechain”
circuit
(C523,
C529,
C553, R523,
and
R527).
The
sidechain
signal
is
then
summed
with
the
main
signal
in
the
encoder/
decoder
resulting
in
the
10
dB
boost.
With
the
DOLBY
Switch
set
to
REC
II,
the
encoder/
decoder
functions
as
a
decoder
similar
to
that
described
in
the
following
paragraph.
With
the
DOLBY
Switch
set
to
either
DOLBY
FM,
PLAY,
or
REC
I,
the
Dolby
Decoder
(U503)
decreases
the
amplitude
of
low-level,
high-frequency
signals
10
dB
complementary
to
encoder
signal
processing.
Again,
portions
of
the
incoming
signal
are
applied
to
a
sidechain
circuit
(C555,
C557,
C561,
R543,
and
R545).
The
sidechain
signal
is
then
subtracted
from
the
main
signal
within
the
decoder
and,
since
the
decoder
processing
is
complementary
to
the
encoder
processing,
high-frequency
noise
am-
plitude
is
reduced
10
dB.
F.
TIMES-TEN
AMPLIFIER
The
Times-Ten
(X10)
Amplifier
is
a
non-invert-
ing
operational
amplifier
consisting
of
a
dual
linear
integrated
circuit
(U201)
and
a
constant-
current
source
(Q211)
in
the
output.
Like
the
Phono/Mic
Amplifier,
negative
feedback
sets
the
gain
of
this
amplifier
and
establishes
the
frequency
roll-off
points.
A
100-millivolt
input
signal
is
nominally
increased
to
one
voit
through
the
X10
Amplifier
(20dB
gain).
G.
ACTIVE
FILTER
NETWORK
The
Active
Filter
Network
consists
of
cascaded
filter
components
at
the
input
of
a
non-invert-
ing,
unity
gain
Filter
Amplifier
(Q213
and
Q215)
with
a
constant-current
source
(Q217)
in
the
output.
Associated
switches
connect
appropriate
filter
components
in
the
amplifier
feedback
circuit
for
a
12-dB-per-octave
rol!
off
at
either
30Hz,
5KHz,
or
9KHz.
Frequency
response
is
flat
through
the
network
when
the
filters
are
not
activated.
Characteristic
curves
for
the
Active
Filter
Network
are
shown
in
Section
2.
H.
TONE
CONTROL/TURNOVER
NETWORK
The
Tone
Control/Turnover
Network
consists
of
the
BASS,
MID
and
TREBLE
Tone
Controls
and
the
250Hz
and
4KHz
TURNOVER
circuit
connected
across
the
input
and
feedback
loop
of
the
inverting,
unity
gain
Tone
Amplifier
(U203).
Feedback
control
is
used
to
shape
the
frequency
response
at
the
Tone
Amplifier
out-
put.
With
the
TONE
Controls
raised
toyvard
“boost’’
position,
the
forward
signal
is
strongest
and
the
feedback
weakest.
When
lowered
toward
“cut’’
position,
the
TONE
Controls
attenuate
the
forward
signal
and
the
feedback
signal
is
dominant.
The
TONE
Controls
are
variable
over
a
range
of
approximately
+
1OdB.
Activating
the
250Hz
and/or
4KHz
TURN-
OVER
circuit
shifts
the
frequency
locus
(tturn-
over)
points
for
the
BASS
and/or
TRE
BLE
TONE
Controls
respectively,
as
shown
in
Sec-
tion
2.
1-7