Dual C 844 - Page 5

Description of functions
Analog section
Playback
The voltage
induced in the
playback head
(approximately 300 IN
du -
ring playback of the
DIN reference
level) is first of all
amplified by
501 and Q 502
and
correspondingly equalized
with the
negative
feedback
network R 509,
R 508 and C
508. The frequency
response at
4
kHz 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). In 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 501 is the middle
position.
Changeover of the equalization
from 120 s to 701./s is
realized
by the
tape type selector switch S 21 - 3 which causes 0
505 to
become for-
ward-biased. At
the 9.5 cm/s speed,
transistor Q 506 switches over to
35
1.4s whilst 0601 renders
transistor 0 505
reverse-biased. During play-
back of the Dolby reference level (200 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,Q 504
and VR 502 to the input of the Dolby
circuit IC
103, Pin
5. If the
Dolby selector
switch S 22 is switched off (0
114 forward-biased), the
signal is amplified
in a linear manner by
approximately 26 dB within
the Dolby circuit whilst
amplification is frequency and
level-dependent
when the Dolby circuit is
switched on. The output
signal is routed from
pin 7 (IC
103) to the input
pin 2 (IC 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, IC 103).
The output
signal is
routed from Pin 7 (IC
104) to
the relay
RY 1 which realizes
the
source-tape monitor
function. During
playback, RY 1 and
the mo-
nitor switch S 24
are inoperative
and, irrespective
of the position of
the
monitor switch, the
tape signal is
routed through the
amplifier IC 302
to the outputs DIN,
LINE and MON. The
playback signal is
also routed
through R
531 from the LINE
OUTPUT to
the headphone
amplifier
IC
601 and through R
284 to the VU meter
amplifier
0273.
In
order to prevent switching
noises from reaching the
output sockets,
the output signal is muted with Q 271 (see
"muting")
when the follo-
wing functions
are selected: stop,
pause,
record, standby, fast
forward
and rewind.
AFC compensation
for IC 104 is realized with the transistor 0 120.
120 is control led by IC
103.
Music finder
The
music finder scan
signal
(active
LOW, IC 409, Pin 31)
is
routed
from the
processor to
transistor 0414,
this becomes
reverse-biased and
enables
the input of
the music
finder amplifier
IC 403, Pin
2. The AF
signal is picked up
by the Dolby
circuit IC
103, Pin 3 and is
amplified
with IC 403. From the output (Pin 1),
the
signal is
routed
through tran-
sistor
Q 413, which
operates as a
limiter, to Pin
6 of IC 403.
IC 403
(Pins
5,6,
7)
operates as a flipflop.
A
static signal
is applied at
the output Pin
7 and, os the
result of
this,
PIECE
OF MUSIC is
active HIGH. If a
SPACE is
recognized between
the
pieces of
music, the output
changes from
HIGH to
LOW. This signal
is
routed to Pin 38 of
the processor IC 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
amplified by the
low-noise
IC 301,
whilst the
signal from
the DIN
input
is
amplified
by Q 272.
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
amplifiers Q
101
and
0 102.
From here,
the signal is
routed to
the input
Pin 5 of the
Dolby circuit IC 101. With
the
MPX switch S 23,
the
MPX filter is
con-
nected via transistor Q
105 and
0
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
Q 107
reverse-
biased (S 22
set to position (3).
AFC compensation is carried
out
for IC
101 with
transistor Q 111.
0111 is control led by IC
102.
In
order to
prevent
interference of
the Dolby
circuit when
recording,
the high
frequency components
os from
10
kHz (- 3 dB)
to 20
kHz
(- 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
0 104
(forward-biased). A HIGH
active
control
signal is applied to the
base of Q 104.
In
the
playback branch,
treble
attenuation is
corrected with
the de-
skewing
circuit C 252
and L 102 at
the output
amplifier IC
302. This
circuit is activated with 0 121
(forward-biased) in
Dolby
C mode.
Within the
Dolby
processor,
the
signal is
branched to
two
different
outputs,
Pin 3
and Pin 7
of IC
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 IC
102. During Dolby B mode, C mode is switched off by
Q 113 (forward-biased). The
output signal of Pin 7 (IC 102) is routed
through VR 504 directly to the recording amplifier IC 602. The recor-
ding current is set with VR 504. Depending on
the tape type, the level
(sensitivity)
is set with the tape type selector switch S 21-2 and the
equalization is set with S 21-1. Additionally, and due to the tape speed
of 9.5 cm/s, the equalization time constant is switched over with Q 509
and Q 511 (both forward-biased). When the tape speed of 4.75 cm/s is
selected, Q 510 is forward-biased and 0509 and 0511 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 the type type selec-
tor switch S 21-6, 0 605 controls transistor 0 604 which influences 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 603
(record = HIGH
signal of the base), Q 604 becomes forward-biased and a voltage of ap-
proximately 27 V is applied to the transistor 0610. The record HIGH
signal is also routed through R 606 and D 618 to 0612 which renders
Q 611 forward-biased. Via diode D 617, transistor Q 610
becomes for-
ward-biased due to the switching of Q 611 and the former transistor
activates the oscillator OSC 1. The DIN output is
switched off with
relay RY 301 during
recording mode.
Fade edit
With
the pushbutton S
27 ON, the
supply voltage is
applied to IC 604
and, via C
603, the
flipflop IC 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, a
HIGH
level is
applied to Pin
6 of IC 604.
The output Pin 3
changes to
HIGH
and thus
0 608 becomes
forward-biased, 0
609 becomes
reverse-biased
and a positive
voltage builds
up at the base of
0 610. The
time-deter-
mini ng
factor is C 604. Depending
on the base voltage,
0610 becomes
forward-biased and thus
determines the amplitude of
the erasure cur-
rent. With the
HIGH level from S 28 III..
via D 612 at Pin 13 of IC
604,
the output Pin 10 changes from LOW
to HIGH, 0 607 is switched on
with
HIGH via IC 603 and the red LED
RECORD lights up. The
HIGH
signal from
Pin 10 is also routed through D
606 to Q 603 which swit-
ches on the oscillator.
Fade in: When the pushbutton 29
(IN) is operated, a HIGH level is
applied to
Pin 1 of IC 604, the output
Pin 3 changes to LOW, thus
Q 608 becomes reverse-biased
and 0 609 connects C 604 via R 639
to
0 V. Via the diode D 620, the
HIGH level is routed from the output Pin
4 (IC 604) via the differentiator C 606 to Q
612 which briefly causes
611 to become forward-biased and thus charges up C
605. Q 611 be-
comes reverse-biased and C
605 is discharged via R 641. Thus, a positive
voltage
with a decreasing level is applied
to the base of 0 610 which be-
comes reverse-biased depending on the
base voltage and thus causes the
erasure current to decrease.
When
the pushbutton ON (5 27)
is released, 0607
(LED
RECORD is
extinguished) and Q 603 becomes
reverse-biased and the oscillator is
switched off. In order to
prevent the inadvertent erasure of music cas-
settes (erasure tab
removed) with the fade edit facility,
transistor Q 606
is forward-biased (HIGH signal at the base = record
safety contact open)
and thus the
flipflop IC 604 is prevented from functioning.
Monitor
During playback
(0 306
reverse-biased), the relay RY
1 is idle and the
off tape signal
from IC 104 Pin 7 is
directly switched to the output
amplifier IC 302. In
recording mode, the signal from IC
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 Q
306, this becomes
forward-biased, relay RY
1 is energized
and switches over to
the source. In this
way, the monitor
switch S 24
begins to function. If the deck is
switched over to "tape", S 24
applies
a LOW
signal to the base of 0 306
and this becomes
reverse-biased.
Relay RY 1 is
de-energized and
switches to "tape". In 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
filter T 501.
Muting, A ut o -S
pace
The recording
amplifier and
the LED
peak display are
muted during
all
functions except
RECORD.
This control signal
MUTING RA
(record
5