Technics SU-Z35

Hi POWER AMPLIFIER PROTECTION
e Short-circuit of speaker terminals
Ty
OBWN
If
speaker
terminals
are
short-circuited,
a
high
level
current
will
flow
to
power
amplifiers
Q5
and
Q6,
causing
the
voltage
across
emitter
resistor
R5
to
increase.
. Voltage across R5 causes overload detecting transistor Q7 to turn ON.
. Emitter voltage of Q7 (ground potential) goes to terminal @ of IC302 through R8.
. Voltage at terminal (%) is transmitted to terminal @ of muting IC (1C401).
. When the terminal ©) of 1C401 reaches OV, the muting circuit of 1C401 operate.
The muting circuit operate, the voltage of terminal () become OV, and then power supply to the initial stage amplifier and
driver stage of I1C302 is discontinued.
Note:
1.
Terminal
@)
of
1C401
supplies
power
to
drive
circuit
of
power
amplifier
1C302,
and
supplies
control!
voltage
to
muting circuit of voltage amplifier 1C301.
2.
1C401
is
provided
with
muting
function
to
prevent
shock
noise
during
power
ON/OFF
in
addition
to
power
amplifier
protection.
1C302
SVISTK2028B
Power amplifier
1C301 Be)
AN7062 ¢
VOLTAGE AMP re >
SP
Pt d
1 _
C331
’
<
° oO
(>
a2s$7
wo @
- 6+ --@-@--
—_
+Vcc
|
constant
SP
1 —_
C332
Be
[ \
!
i
|
|
| Right channel
i
|
|
I
|
|
|
|
i
transformer (2)
|
|
|
i
\
y t
C403
From
power
|
RIs
R318 @
Ic401
|
:
AN7072N
ee
ee
+———®
ANSE
Mute
&
protection
circuit
1
eee le eee el eC —_
[Fig. 7]