Panasonic Technics SA-800 User Manual

SA-800 SA-800
POWER AMP DRIVE/PROTECTION CIRCUIT POWER TRANSISTORS
TRANSFORMER TAP SELECTION CIRCUIT
&
FUSES
FM RF CIRCUIT
VARIABLE CAPACITOR
FM IF AMP/AM CONV.
RELAY
(PROTECTION/
FM IF AMP
FM MPX
LOGARITHM
MPX
FILTER
COMPRESSOR
CIRCUIT
TECHNICAL GUIDE
™@
AUTOMATIC
SELECTION
CIRCUITRY
FOR
MAIN
AMPLIFIER
POWER
VOLTAGE.
(TRANSFORMER
COIL
TAP)
This
circuitry
functions
to
maintain
the
main
amplifier
in
a
stabilized
operating
condition
by
detecting
the
DC
resistance
of
the
speakers
connected
to
this
unit,
and
then
making
the
changeover
to
the
high-voltage
power
trans-
former
coil tap
if
the
load
is
80
or
more, or
to
the
low-voltage
tap
if the load
is
61
or
less.
MAIN
(SPEAKER)
AC
120V
o—{1)
REMOTE
|
{
—¢-0--0—{R) MAIN
i
(SPEAKER)
|
ro SPEAKER DC RESISTANCE o—(R) REMOTE
DETECTION CIRCUIT | i |
| RELAY DRIVE CIRCUITRY BY
| |
|
|
I
|
D903
Fig. 1
Operation principles
1.
If
speakers
with
an
impedance
of
62
or
less
are
to
be
con-
ea
nected
to
the
left
and
right
“MAIN”
or
“REMOTE”
speaker
9
terminals
(Fig.
2).
-—+-
COMPARATOR $ $
After the speakers are connected to this unit, turn on the
power switch. The muting circuitry of this unit will function 6V
for about 5 seconds, until output from the main amplifier .
appears
at
the
speaker,
thus
maintaining
the
muting
relay
1c301
3
aiveor
(RLY601)
in
the
condition
shown
in
figure
1.
Speaker
impe-
teaon
dance
is
detected
during
this
interval.
With
RLY601
in
the
:
2
3]
condition
shown
in
figure
1,
the
speakers
will
be
connected
in
hr
parallel to point @) of the speaker DC resistance-detection
circuitry, and the voltage at point (b) will decrease. With a
reference
voltage
of
1.5V
applied
to
terminal
@
of
the
Fig.
2
comparator (IC901), a voltage of 6V will appear at terminal
@
when
the
voltage
of
terminal
@
becomes
lower
than
that
of
terminal
@.
In
other
words,
the
output
voltage
of
terminal
8)
activates
TR902
and
TR901
of
the
relay-drive
circuitry,
and
the
tap-selection
relay
(RLY701)
switches
over
to
the
low-voltage
tap.
When
80
speakers
are
connected
to
the
“MAIN”
and
“REMOTE”
speaker
terminals
and
both
speaker
switches
are
on,
total
impedance
becomes
422,
and
operation
becomes
the
same
as
when
speakers
of
6
or
less
are
connected.
2. lf speakers with an impedance of 89 or more are to be
connected to the left and right ‘“MAIN” or “REMOTE”
speaker terminals (Fig. 3).
COMPARATOR
The detection method is the same as when Speakers with an
impedance of 6 or less are connected. In this instance,
however, the voltage of terminal @ of the comparator
becomes higher than the reference voltage of terminal @),
and no output appears at terminal 8) . AS a result,
q because the relay-drive circuitry does not operate, the relay
(RLY701) remains switched to the high-voltage tap.
Fig. 3
.
If
a
speaker
with
an
impedance
of
8
is
connected
to
the
left
“MAIN”
or
‘“REMOTE”
speaker
terminal,
and
a
40
speaker is connected to the right terminal.
The detection method is the same as when speakers with an impedance of 82 or less are connected. In this instance,
however, the 6V voltage can be obtained only from terminal 3) of the right channel comparator (1C902). This
voltage is applied to terminal @) of the left channel comparator (1C901), and then, because the voltage of terminal
@ of 1C901 becomes high, it can be seen that the voltage of terminal @ of 1C901 becomes equivalently low. As
a result, a 6V voltage can be obtained at terminal B) of 1C901, and the relay (RLY 701) switches the power trans-
former over to the low-voltage tap. This operation is the same as when a 42 speaker is connected to the left speaker
terminal and an 8Q speaker is connected to the right terminal.
Operation principles 1, 2 and 3 above are an explanation of the circuitry which detects speaker impedance after the
power is turned on and until the main amplifier output is emitted to the speakers. The following is an explanation
of the circuitry which detects impedance when the output is being emitted.

Panasonic Technics SA-800 Specifications

General

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