4.
Circuit
Descri
ption
4.1
L
and
R
Channels
See
circuit
diagram
230.8518
8,
sheet
1.
The
signals
on
the
left
and
right
channels
are
taken
to
two
identical
signal
paths
either
via
BulO
and
Bull
or
via
St101.0abc
and
.9abc.
Switch
8101
per-
mits
the
inputs
to
be
switched
off
or
the
internal
sinewave
generator
to
be
cut
into
circuit.
tors
switchable
in
steps
of
3
dB
and
0.5
dB
and
decoupled
by
buffer
stages.
The
preemphasis
sections
R122/C101
(R162/C115)
are
followed
by
further
buffers
B101
(B105)
whose
feedback
paths
include
attenuator
sections
switchable
in
0.1-dB
steps.
The
Cauer-type
lOWpass
filter
L101
to
L104
(L105
to
L108)
suppresses
frequen—
cies
in
the
range
above
15
kHz;
it
has
notches
at
38.8,
19.2,
18.1
and
25.1
kHz.
After
inversion
in
B102
(B104),
the
signals
are
passed
on
to
the
resistor
chain
of
the
coder
(lines
D
and
G
in
circuit
diagram).
Correction
signals
for
improving
the
crosstalk
are
also
required
(lines
A,
B,
E,
F).
Link
ERlO}
selects
the
channel
associated
with
mono
operation.
The
amplifier
T111
to
T116,
which
has
a
two-stage
feedback
circuit,
feeds
the
L
;
Rm;
31.150
and
St101.8abc
by
means
of
transformer
TrlO}.
The
deemphasis
section
R206/C141
in
the
feedback
path.is
switched
with
8105
sum
outputs
M
(=
and
cancels
the
preemphasis
in
the
left
and
right
channels.
4.2
Coder
See
circuit
diagram
230.8518
8,
sheet
2,
and
oscillograms
Fig.
6a.
The
coder
operates
on
a
principle
which
is
based
on
the
switching
technique.
The
"hard—switching"
procedure
at
38
kHz
is
replaced
by
graded
switching
in
14
steps.
In
this
way
unwanted
sidebands
only
occur
at
the
13th
harmonic
and
can
be
filtered
out
by
a
simple
lOWpaSS
filter.
”Soft-switching"
is
performed
by
the
resistor
chain
R231
to
R262
between
the
signal
lines
”-L"
(line
D
in
circuit
diagram)
an
”-R”
(line
G)
and
by
the
field-
effect
transistors
T121
to
T128
that
are
switched
in
one
after
another.
The
cor—
rection
signals
”—L'"
and
”-R'”
(lines
E
and
F)
improve
the
coding
at
the
moment
of
subcarrier
zero
crossing.
The
switching
pulses
for
the
field—effect
transis—
tors
are
generated
in
the
shift
register
BlO8/B109
and
delivered
in
the
correct
R
38122
-
l7
