Panasonic Technics SA-800 User Manual

4. Trigger-pulse-generation
circuitry MAIN AMP
Let> RELAY B
oe, EN reea : 2. ~” OLEFT SPEAKER
This
is
circuitry
which
gene-
°
OOFF
PULSE
OUT
ere
rates a positive pulse when a $13 @1 (s13)
speaker switch is switched 1 OON C913 D909
from off to on while this unit ie tt + ®
is operating, and generates a Baie bss fra
negative pulse when the +Bo WWW 1 +¢ © 6)
switched from on to off (Fig. 4). ool freus
@ When the speaker switch
(S13) is on, positive vol- Fig. 4
tage (+B) is charged to C912 and C913.
(@)
When
the
speaker
switch
is
switched
from
on
to
off,
the
charge
applied
to
C912
is
suddenly
discharged,
D908
becomes
forward
biased,
and
a negative
pulse
can
be
obtained from
in
figure
4.
@
When
the
switch
is
switched
from
off
to
on,
a
positive
voltage
(+B)
is
suddenly
charged
to
C913.
D909
becomes
forward
biased,
and a positive
pulse
can be
obtained from
@
in
figure
4.
5, When a speaker switch is switched from off to +B
on.
D906
In this instance, as explained in item 4, a posi- re 7
tive pulse is generated from the trigger-pulse-
generation circuitry. This pulse is applied to O3sec
the mono-stable multivibrator shown in figure
5. TR905 of this circuitry is usually maintain- me to ON
ed in the “off’’ condition, and TR906 in the
“on” condition. When a positive pulse is
applied to the base of TR905, it becomes on,
and the collector becomes ground potential. Fig. 5
However, because this transistor becomes on only at the instant that the positive pulse is applied, the collector
also returns to positive potential about 0.3 second later. During this interval of about 0.3 second, the TR907
muting-relay-drive transistor becomes off, and RLY601 becomes in the condition shown in figure 1. Then speaker
impedance is detected as described in items 1, 2 and 3, and the tap-selection circuitry is activated.
RLY601 to OFF
. When a speaker switch is switched from on to off
In
this
instance,
as
explained
in
item
4,
a
negative
pulse
is
generated
from
the
trigger-pulse-generation
circuitry.
This pulse
is
applied
to
the
mono-stable
multivibrator
shown
in figure
6.
TR903
of this circuitry
is
usually main-
tained
in
the
“on”
condition,
and
TR904
in
the
“off”
condition.
TR903
becomes
off
only
at
the
instant
when
a
negative
pulse
is
applied
to
its
base,
and
positive voltage
appears
at
the
collector.
C909 is
charged
by this voltage,
and,
at
the
same
time,
TR904
becomes
on.
When
TR904
becomes
on,
the
collector
becomes
ground
potential,
and,
in
the
same
way
as
explained
in
item
5,
this
circuitry
also
returns
to
the
“off”
condition
after
about
0.15
second.
In
this
way,
the
TR904
collector
and
the
impedance
detection
circuitry
are
connected
by
way
of
D903.
During
the
time
that
the
TR904
collector
is
ground
potential,
D903
becomes
forward
biased,
and,
therefore,
the
comparator
function
is
simultaneously
reset
when
TR902
of
the
tap-selection
relay-drive
circuitry
becomes
off.
In
addition,
the
collector
potential
of
TR903
also
returns
to
ground
potential
after
about
0.3
second.
At
this
time,
the
charge
until
now
applied
to
C909
is discharged,
and the
negative
pulse
here generated
is
applied
to
the base of
TR906.
Then
TR906
becomes
off,
and,
as
explained
in
item
5,
the
collector
of
TR905
becomes
ground
potential,
and
the
negative
pulse
turns
off
the
TR407
muting-relay-drive
transistor
for
about
0.3
second.
During
this
interval,
the
Operation
of
the
speaker
DC
resistance-detection
circuitry
is
as
already
explained
in
items
1,
2
and
3.
Note
that,
as
shown
in figure
6,
time
delays
occur
in
each
of
the pulses.
oe FROM
4 aN ae = SPEAKER SWITCH
OV |
ay
015
oi
Ss
RESET
PULSE
2Sec ov-—-
\
he1015sec
+—~—
C909
RESET
PULSE
ov
CHARGE
PULSE
am D903
ov o—p
+
0.i5sec i TR9O6
eae INPUT PULSE
- RLY601
OV
OFF
PULSE
03sec
O3sec
[RELAY PULSE | PULSE
Fig. 6
@ POWER-INDICATION CIRCUITRY
fe) 0
POWER AMP Lr aaa Y ¥ Wr
The power amplifier output signal is attenuated
by the sensitivity selector, and is applied to the
logarithmic-compression circuitry. In this cir-
cuitry, as shown in figure 7, the output chara- forte Sencetn
cteristics change logarithmically in relation to CIRCUITRY
input, and the output is applied to the window Fig. 7
comparator IC. Here, the pulse waveform -—
becomes as shown in figure 8, and the indicator
illuminates according to the input of the IC INPUT
(the output of the power amplifier).
WINDOW
COMPARATOR;
LOGARITHM
COMPRESSOR
WINDOW
COMPARATOR IC
(paxtals e
LIGHT UP PULSE
Fig. 8
_ (Low) a . oes
1,2 SOM FICT m@ TONE-CONTROL CIRCUITRY
ee > ‘ on (TONE)
TREBLE i gee Configuration is as shown in figure 9. Bass and
(HIGH) Y] treble are the BAX type of control circuitry,
= a= im ~~] and a bandpass filter is used for control of
intermediate frequencies. If the middle control
(eabet is moved in direction A, a valley-like charac-
AAI S crenteioe teristic can be obtained. If it is moved in
TY] > direction B, a peak-like characteristic can be
obtained. Note that the input signal will bypass
the tone-control circuitry if the acoustic cont-
Fig. 9 rol (“TONE”) is set to the “OFF” position.
BAND PASS FILTER
B PROTECTION CIRCUITRY
When DC voltage appears at the speaker terminals of this unit, there is protection circuitry to shut off the speaker
relays and thus protect the speakers from damage, as well as protection circuitry which short-circuits the input and
prevents the signal from being applied to the main amplifier, thus protecting the power amplifier from damage caused
by overload or short-circuitry of the speaker terminals.
Sisinecitais sieinatsescias bt

Panasonic Technics SA-800 Specifications

General

Brand	Panasonic
Model	Technics SA-800
Category	Stereo Receiver
Language	English