Description Of Functions - Dual C 844 Serviceanleitung

C
Description of functions
Analog section
Playback
The
voltage induced
in the
playback
head
(approximately 300
l.tv
du-
ring playback
of the DIN
reference
level) is
first of
all amplified
by
O
501 and
Q
502 and correspondingly equalized
with the
negative
feedback
network
R
509,
R
508
and C 508. The
frequency response at
4 k1z
can
be slightly modified by closing
or
opening the strap
J
1-
The
high
frequency
range can be corrected
by
replacing
the
capacitor C 509
(plug-in type). ln
the case
of the
9.5 cm/s tape speed,
the
playback fre-
quency
response
is
corrected
within the 20 kHz
range
with VR 501
and
L 501.
VR
501
should not
be adjusted.
Adjustment
is
carried
out at the
factory, The
basic
position of
VR
50i
is
the middle position.
Changeover
of
the equalization
from
'120
Lts
to
70pts
is
realized by the
tape
type
selector
switch S
21
3 which
causes
O
505
to
become
for-
ward-biased.
At
the 9.5 cm/s
speed,
transistor
O 506
switches over
to
35
lÄ whilst
O 601 renders
transistor
O
505
reverse-bimed.
During
play-
back
o{
the Dolby
reference level
(2O0 nWb/m), the playback
level
at
LINE
OUT
is
set
to
550 mV
with the VR
502.
The blayback
signal
is routed through the
stopper
circuit T
501
,
O 504
and
VR 502
to
the input
of
the Dolby
circuit lC
103, Pin
5.
lf
the
Dolby
selector
switch
S
22
is
switched
off
(O
ll4forward-biased),the
signal
is amplified in a linear
manner
by approximately 26 dB
within
the
Dolby circuit whilst
amplif ication
is
frequency
and level-dependent
when the Dolby
circuit
is
switched on. The
output
signal is
routed from
pin
7
(lC
103)
to
the input pin
2
(lC
104)
of the Dolby circuit
via VR
104.
Also
in
this
case,
when
the Dolby circuit
is switched
off
(Q
116
forward-biased). the signal
is amplified by
approximately
26 dB in
a
linear manner (referred
to the
input level Pin
5, lC
103). The
output
signal
is
routed
from
Pin
7 (lC
104)
to
the relay
RY
1
which
realizes
the
source-tape
monitor function. During playback,
RY
1
and
the mo-
nitor switch
524
are
inoperative and, irrespective
of the position
of
the
monitor switch, the
tape signal
is routed through the
amplifier
IC 302
to
the outputs
DlN,
LINE
and MON. The playback signal
is also
routed
through R 531
f
rom
the
LIN
E
OUTPUT
to the
headphone amplif ier
lC 601 and
through
R
284 to the VU meter amplif ier Q 273.
ln
order
to prevent switching
noises
from
reaching
the output
sockets,
the
output
signal
is muted
with
O
271 (see
"muting")
when the
follo-
wing functions
are selected: stop, pause,
record, standby, fast forward
and rewind.
AFC
compensation
for lC
104
is
realized
with the
transistor O'120.
O
120
is
controlled
by lC
103.
Music
finder
The
music
f
inder scan
signal (active LOW, lC
409, Pin 31) is
routed
from the processor to
transistor Q
4
1
4,
this becomes
reverse-biased and
enables
the input
öf the
music
finder amplifier lC 403, Pin 2. The AF
signal is
picked up by the Dolby circuit IC 103. Pin
3 and is amplified
with
lC
403. From the
output
(Pin
1
),
the signal is routed through tran-
sistor
O 413, which
operates as
a
limiter,
to
Pin
6
of
lC
403.
lC
403
(Pins
5, 6, 7) operates
as
a
flipflop.
A
static
signal
is applied at
the output
Pin
7
and, as
the result
of
this,
PIECE
OF
MUSIC is active
HIGH.
lf
a
SPACE
is
recognized between
the pieces
of
music,
the output
changes
f
rom
H
lG H
to
LOW.
Th is signal
is
routed
to
Pin 38
of the processor lC 409
via R
432.
Recording
Three
different sources are available
for
recording.
The LINE input
is
switched
off
when
the DIN socket is
used.
The signal at
the Mic input
is
amplifieqby
the low-noise lC
301
,
whilst the
signal f
rom the
DIN input
is
amplifi-ed
bV
A272.
The
Mic
signal is
routed
to
the recording
level
control
VR
101 and
the DIN
or LINE
signal is
routed
to the
recording
level
control
VR
102,
both of which act on the mixing amplif iers
O
101
and
O
102. From
her.e,
the
signal
is routed
to the input Pin 5
of
the
Dolby
circuit lC
101.
With the
MPX
switch
S 23,
the MPX
filter
is
con-
nected viaJransistor
O
105 and
Q
106
(both
forward-biased) in order
to
suppress
any
existing
pilot tone
residues
when recording radio
broad-
casts.
The Dolby
circuit is switched
on
by
rendering
O
107
reverse-
biased
(S 22selIo position
B).
AFC compensation
is
carried
out
for lC
101
with
transistor
O
111.
O
111
is
controlled
by lC
102.
ln
order
to
prevent interference
of
the Dolby
circuit
when recording,
the high frequency components
m from
10
kHz
(-
3
dB)
to
20
kqz
(-
12
dB)
are attenuated
by
the skewing
filter
(C '153
and
L
101).
When
the Dolby
selector
switch S 22-2 is
set
to
position
C, the
filter
is
connected
with
the transistor
O
104
(forward-biased). A
H
IGH
active
control
signal is
applied
to the
base
of
O
104.
ln
the playback branch,
treble
attenuation is corrected
with
the
de-
skewing
circuit
C
252
and
L
1O2
aI the output amplifier
lC 302.
This
circuit
is
activated
with O 121 (forward-biased) in Dolby
C
mode.
Within
the
Dolby processor,
the
signal
is
branched
to
two different
outputs, Pin 3 and Pin
7
of lC
101
. The signal
from
Pin
3
which
is
not
influenced
by the
Dolby process is routed
to
the monitor relay R
41
when the
source
setting
is
sellected and used
as
the
source signal. The
signal
from
Pin
7
is routed
through
VR
103
to
the input Pin 2
of
the
Dolby
circuit lC
1O2.
During Dolby B mode, C mode
is
switched
off
by
O
1'13
(forward-biased).
The
output
signal
of Pin
7 (lC
102) is routed
through
VR 504 directly
to
the recording
amplif
ier
lC 602. The
recor-
ding current
is set
with
VR 504.
Depending on
the
tape
type, the
level
{sensitivity) is set
wlth
the tape
type
selector
switch S 21-2
and
the
equalization is set
with
S
2'l-1.
Additionally,
and due
to
the tape
speed
of
9.5 cm/s, the equalization
time constant
is
switched over
with O 509
and
O
511
(both
forward-biased). When
the tape
speed
of 4.75
cm/s
is
selected,
O 510
is
forward-biased and O 509 and O 511 are
reverse-bia-
sed.
The recording signal is routed
to
the recording
head
through
the
stopper
circuit
T 502. The
bias is
mixed
to
it
with
vR
505.
By connection of the
resistors R 618
to
R 623
with thetype
typeselec-
tor
switch
S
21-6, O 605
controls transistor
O 604
which
inf luences the
oscillator OSC
1
in
such a
way that
an
optimum operating
point
is
achieved
for
the
various tape types. The erasure
current
can be changed
with the
strap over diode D 609.
With transistor
Q
6O3
(record = HIGH
signal
at
the
base),
O 604 becomes forward-biased and
a
voltage
of
ap-
proximately
2-7
Y
is applied
to
the transistor O 610. The record HIGH
signal is also
routed through R 606 and D 618
to
O 612 which
renders
O 6i
1
forward-biased. Via diode D 617, transistorO
6'1
0 becomes
for-
ward-biased due
to
the
switching
of O
61
1 and
the former transistor
activates
the oscillator
OSC
1.
The DIN output
is
switched
off
with
relay RY
3O1
during recording mode.
Fade
edit
With the
pushbutton
S
27 ON, the supply
voltage
is
applied
to lC
604
and,
via
C
603, the flipf
lop lC
604 is set
to
its
defined initial
position.
(Pin
3
LOW, Pin
4
HIGH, Pin 10
LOW).
The pushbutton ON
must
remain
depressed
for
all
following
FADE
EDIT functions'
Fade
out:
When
the
pushbutton
S
28
(OUT)
\
is
operated, aHIGH
level is
applied
to Pin 6
of
lC 604. The
output Pin 3
changes
to
HIGH
and
thus O 608
becomes
forward-biased, O 609 becomes
reverse-biased
and a positive
voltage
builds up at the
bae of O
610. The timedeter-
mining
factor
is C 604. Depending on the
base
voltage. O 610
becomes
forward-biaed and thus determines
the
amplitude
of
the
erasure cur-
rent. With the HIGH level
from
S 28
\-
via
D
612
at Pin
13
of
lC 604,
the
output Pin
10 changes
from
LOW
to
HIGH, O 607
is
sw;tched on
with
HIGH via
lC 603
and
the
red
LED
RECORD lights up. The HIGH
signal
from Pin 10
is also
routed through D 606
to
O 603 which swit-
ches
on the oscillator.
Fade
in:
When
the
pushbutton 29 (lN)
-J is
operated, a
HIGH
level
is
applied
to
Pin
1
of
lC 604, the output Pin 3
changes
to
LOW, thus
Q
608 becomes
reverse-biased
and
O
609
connects
C
604via
R
639to
0 V. Via
the
diode
D 620,
the HIGH level is routed
from the output
Pin
4
(lC
604) via the differentiator C
606
to O
612
which briefly
causes
O
6l
1
to
become
forward-biased
and thus charges
up
C 605. O 611 be-
comes reverse-biased
and
C
605
is
discharged
via
R 641. Thus,
a
pos;tive
voltage
with
adecreasing level
is
applied
to
the
base
of O 610
which
be-
comes reverse-biased
depending
on the
base
voltage and
thus
causes
the
erasure
current to
decrease.
When
the pushbutton
ON
(S 27)
is releaed.
O607 (LED
RECORD
is
extinguished) and
O
603
becomes reverse-biased
and
the
oscillator
is
switched
off.
ln
order
to
prevent the
inadvertent erasure
of
music
cas-
settes
(erasure
tab removed)
with
the fade
edit facility,
transistor O 606
is
forward-biased (H
lG H signal at
the
base
= record safety contact
open
)
and
thus the
flipflop
lC 604
is prevented
from
functioning.
Monitor
During playback (O 306
reverse-biased),
the relay
FY
1
is idle and the
off
tape signal
from lC
104 Pin
7
is
directly
switched
to
the
output
amplifier
lC
3O2.
ln
recording mode, the signal
from lC
101 Pin
3,
which is uninfluenced
by the Dolby process, is routed
as
the
source
signal
to
relay
RY
1. Due
to
the signal RECORD (HIGH
active) at the
base
of
O
306, this becomes
forward-biased, relay
RY
I
is energized
and switches over
to
the source.
ln this
way,
the monitor switch
S
24
begins
to function.
lf
the deck
is
switched
over
to
"tape",
S
24
applies
a
LOW signal
to
the
base
of O
306 and
this
becomes reverse-biased.
Relay
RY
'l
is
de-energized and switches
to "tape".
ln this way, the in-
formation
already recorded
on the
tape can
be
monitored.
As
crosstalk
of
the bias
within the record/playback head is unavoidable in
this
ope-
rating mode,
the
bias must be suppressed
by the
f
ilter
T 501.
Muting, Auto-Space
The
recording
amplifier and
the
LED peak display
are
muted
during
all
functions except
RECORD.
This
control
signal
MUTING RA (record