Dual C 822 Serviceanleitung Seite 6

Circuit description C 822
Analog
Seaion
Playback
The
AF
voltage
of
approx. 300
pV (DlN
reference
level) produced
by
the playback
head,
is
amplified by
transistors
O
1
02 and O
1
03.
lt
then
passes
a
negative
feedback
network,
consisting
of
R
153,
R
156
and
C
137
for
equalization. Capacitors C 131, C 132 and C 133 can
be
con-
nected in
such
a
manner
as
to provide
correction
of treble
response
during
playback
by
changing the tape head resonant
frequency.
whereas swit-
chover
f
rom
120 lsec
to 70l.bec equalization
time constant
is
accompli-
shed
by
O
103.
While applyingthe Dolby
reference
level
of 200
nWb/m,
the playback
level
attheCinch outputjacks issetto 580
mV
with VR
103.
This adjustment
is
very important
to
assure adequate
operation
of
the
Dolby
system.
The
playback signal is connected
to
the
Dolby input
(pin
1
of
lC
102)
through
the
REC/PLAY switch
(AAV)
S'1
02.
ln
OFF position of
the
Dolby switch
S
301 ,
the
signal is
amplified
by
26
dB
within the Dolby
circuit,
whereas amplif ication
will
be
level-
and frequency-controlled
when
the Dolby
system is activted. The
Dolby output
signal
at pin
7
oI
lC
1O2 is
routed to the
headphoneamplifier lpin2 of
lC 103) through
R
EC/PLAY
switch S 103 and
to
the
D
lN output
jack
th
rough
R
EC/PLAY
switch S
105.
To
prevent switching
noise
leakage
into
the
output circuit, the
output
signal is shorted
by transistor
O
105, whereas
the
recording
amplifier
input
will
simultaneously be set
to
OV by
O1O6.
A
high signal
tocontrol
the muting
circuit
is
supplied
by the
tape transport
control
circuit
board
during fast
forward, rewind
and stop
functions.
Recording
This cassette
deck features three
different
recording inputs:
MlC. DIN and LINE. When
a
source
is
connected
to
the
DIN
input, the
LINE input
will be grounded.
After
connecting a monaural
or
stereo
microphone
to the MIC input,
source signals
atthe
DIN and
LINE
inputs
are
cut
off. The MIC
signal is
amplified
by
low-noise
lC
101 ,
the DIN
input signal by O 601, whereas the Ll
N
E
inpul
signal
is
routed directly to
level
control
VR
101
and from
there
to
pin
5
of
Dolby
lC
102 through
the
REC/PLAY switch S 102.
S
201
inserts
a
multiplex filter
to
suppress
pilot
signal
leakage
when
re-
cording FM stereo broadcasts.
The signal
is
subdivided
within the Dolby processor
and routed
to dif-
ferent
outputs: pin 3
and
pin 7 of
lC
'102.
The non-dolbyized
signal
at
pin
3
is
passed
to the monitor output
(LINE OUT), VU
meterand head-
phone
amplifier through REC/PLAY switch
S
103, whereas
the Dolby
siqnal
at pin 7
is routed
to
the
recording
amplifier (O
'l
07 and
O
108)
through REC/PLAY switch
S
'1
O4.
Recording
current
is
adjusted
by
con
tol
VR
i02,
level and equalization
(in
accordance
with
the
tape
used)
by
O
109
through O
1
12.
The recording signal
is
rolrted
to
the recording
head
after passing
a serles
rejector
with VR 105 providing the correct
bias
voltage.
By connecting R
307
through
F
315 by
means
of
tape
se-
lector switches S
401
(Fe),
S
402 (Cr),
S
403 FeCr) and
S
404
(Metal),
the RF
bias
oscillator
is
set
to optimum
operating characteristics
for
either
one
of
the
tape types
to
be
used.
ln
recording mode the monitor
signal
will
be
cut
off
by
R
EC/PLAY switch
S 105.
Level lndicator
ln
recording
as
well
as
in playback mode, the outputsignal
is
passed
to
the
headphone
amplifier
lC
1
03. C
1
46 couples the
output
signal
at
pin
1
of lC
103
to
the meter
amplifier (O
104).
VR
104
is used
for
0
dB
dlal
calibratlon
of
the
VU
meters.
To
compensate
for
the reduced recor-
ding characteristics
at
higher frequencies,
R
1-l2and
C 147 provide
ne
cessary
frequency r€sponse
correction.
Response
at
1O
kHz is
10
dB
higher
than at 400 Hz. An analog meter
with
needle
is used
for
level in-
dication.
lts
dlal scale
is
subdivided into individual
scales
for either one
of
the
tape types
which can be used.
LEDs which
are
connected to the
tape selector switches indicate
tli€ corresponding
sub
dial
scale.
Tape
Transport
Functions
selected
by
operation
of
the
selector pushbutton
switches
such
as
forward, rewind, pause, fast
forward,
fast rewind etc.
are
transfer-
red
as
active low
control
signals to the tape
transport control
I
C
403,
pro-
ducing logic decisions
in form of
static high
signals
at
its
output. These
selected
control
signals
are routed
to
the appropriate transistor
stages
by
means of decoupling diodes
after
passing the time
delay
circuit
com-
posed of
R
430 through
R
433,
C
416 through C42Oand the
AND
logic
interlacing lC 404 which
supplies
a high signal
lDLL AUS). For
better
u
nderstanding
of the switch ing process,
F
F
(f
ast f
orward
)
mode
is
quoted
as an
example: a
high signal is routed
through
diodes D 41'1 and D 416
to
a differentiating (time)
circuir
(C
435lR
438l, ,
turning on
transistor
O 407. This transistor
supplies
an
overvoltage
to solenoid FF for
a pre-
determined
period of time,
whereasO
404appliesthe
0
V livel. This
over-
excitation
assures instantaneous
and reliable activation
of
the solenoid
switch.
After
expiration
of
the preset time
period,
O
406
is
switched
off and D 419
maintains latching
of
the
solenoid
switch
until
Q 404
cuts
off
the supply
voltage
when a low
signal is
applied
to
its
base
by
lC
403
or
DLL ElN,
thus
releasing solenoid
switch
FF.
The
same
principle
applies
to all
other solenoid-activated magnetic
switches.
ln playback mode, FF
and
RW are
excited,whereas the recording
mag-
net
-
normally connected
to
the
0 V supply
-
will
be
excited
in
re-
cording mode by an
overvoltage
from O 410 with
Q
413 and D
418
supplying
the latching
voltage.
The motor
of
the
tape
transport
mechanism is
turned on
by switching
transistor O
4i9
when
a
high signal
is
applied
to
its base
by diodes
D
424
through
D 42-7.
ln DLL EIN status, a low signal
is
applied
to
the
base
of
O
419 through D
414
rc switch the motor
off
.
DLL
The
DLL
system
uses an
opto-electronic infrared light conductor
device
which operates
without
mechanical
contact points.
The lR transmitter
LED 505
is
controlled
by the
free-running oscillator lC
4O2 and
transistor
O 40'1
(period:
1 ms,
frequency:
1
kHz). These pulses warrant
adequate
operation which cannot be influenced
by
equrvalent
light
and
reflection
interference. Photo transistor O 501 converts the light pulses into electri-
cal pulses, which
are
then processed by the comparator lC 402.
When
the
light
path is interrupted
(DLL
EIN),
a
high
signal
will
be
present at
the
output
(pin 7) of
lC 402 during the period of
light interruption
(dark
period).
C
407
is a
blocking
capacitor.
At
the
same
time,
a
high
signal is
present at pin 4.
lt
will
remain
at
high level even
after switch S'l 08
is
closed
(cassette
removed), whereas
a low signal is available
at pin 2 of
lC
401 to control the
DLL
EIN
status.
ln
case
of
Pause or.-Record
func-
tion
or
Pause
only,
O
4i 7
is
turned on by
diodes D
422
and D
423. ln
addition, the
DLL
EIN
status
becomes
active,
turning
on Q 416
and
effecting the stop
function by
applying a
low
signal
to
pin 2
of lC 403.
At
the
same
time,the
Record and
Pause
pushbuttons
are locked
to prevent
erroneous
operation
by a
high signal
(DLL
EIN) at
pin
4
of
lC
401
,
whereas
the
lamp
driver lC
4O1 is
activated
by
a signal
through
D
402
which
is applied
to pin
14, causing
the
STOP
LED
indicator
to
light
up.
Another
tow signal
from
lC 401
pin
2 (DLL
EIN) isappliedtoQ4l9
through
D
41
4, causing
this transistor to cut off the tape transport motor.
Record
Blocking Circuit
Open
contact S 507
activates
the Record
Blocking circuit. When O 418
becomes
conductive,
a
low signal
is
applied to the input
(pin 9)
of lC
4G-
This
will
deactivate
the
recording
circuit
and
prevent the record pushbut-
ton
from
being erroneously operated.
Tape End
Switching Circuit
A
multi slot
magnetic disc
which
is attached
to
the tape
counter
drive
pul ley,
senses
tape
motion
and
transmits
a
"tape running"
signal
to
lC
5O1
.
incorporating
a Hall
sensor
which
responds
to
changes
of the
magnetic
flux
density. Pulses
supplied
by lC
501
are
routed
to
pin
2
of
1C405,
effecting automatic stop
of
the
tape advance
at
tape end. Transistor
O 420 supplies a low signal
through
di-ode
D 430 to cut
off
O
421
.
ln this
condition, the
tape
transport
mechanism is operating.
A
high signal at
pin
1
of
lC 405 activates this integrated
circuit.
lf
no pulses are applied
to pin
2,
lC 405
will
transmit a
low
signal
from its
pin
6
to p;n 2 of
lC
4O3,
which
is
equivalent
to
a STOP signal.
lf
a
high signal
is
applied
to
O
421 either
from diode D 429 {DLL
EIN) or D 428 (Pause),
this
transistor becomes
conductive, connecting
the
low
signal
to pin
1 of
lC 405, thus dlsabling the tape end switching
circuit.
Muting
circuit
The mutinq siqnal
is
supplied
by
transistor O
41i. lf
this transistoriscut
off,
a high
signal
will
be present at
its collector and the muting circuit
is
operative
(see circuit description
of analogsection).A lowsignal
(play,
pause)
at D 431 cuts
ofi A
422, whereas Q 41 1
becomes conductive
after
a
short
time
delay
lC
42Bl and a low
signal
will
be present at the
collector oI C 411to
disable
the muting
circuit. lswillbeactivatedagain
bv hiqh
active
signals
from
diodes
D 432
(rewind/fast forward),
D 431
(STOP) and
D
433
(DLL
EIN)
---