Technics SU-Z55 - Page 23

6.
The
correct
parts
of
power
amplifier
protection.
@
POWER
AMPLIFIER
PROTECTION
©
Short-circuit
of
speaker
terminals
1.
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
(7)
of
1C302
through
R8.
.
Voltage
at
terminal
(7)
is
transmitted
to
terminal
(5)
of
muting
IC
(1C401).
Calculation
circuit
of
1C401
operates
to
eliminate
the
voltage
at
terminal
(3)
of
1C401.
.
On
operation
of
muting
circuit
of
1C301,
the
drive
circuit
of
1C302
stops
operating
and
the
current
from
power
amplifier
also
stops.
Note:
1.
Terminal
(3)
of
1C401
supplies
power
to
drive
circuit
of
power
amplifeir
1C302,
and
supplies
control
voltage
to
muting
circuit
of
voltage
amplifier
|C301.
2.
1C401
is
provided
with
muting
function
to
prevent
shock
noise
during
power
ON/OFF
in
addition
to
power
amplifier
protection.
Seas. oli cet gs
OnrRwhr
1C 302
SVISTK2038B
Power amplifier
iC 301
AN7062
VOLTAGE AMP
eae sangeet men:
Time
6 constant
Right channel
From power !
transformer
Ic 40]
I
|
i |
|
AN7072N
be
|
Mute & protection circuit
\
4A
;
j
Printed in Japan
830610000 (N) KS