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Sharp OPTONICA SM-1616H - Circuit Description - Main Amplifier and Meter; Main Amplifier Circuitry Explained; Meter Circuit Operation

Sharp OPTONICA SM-1616H
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CIRCUIT
DESCRIPTION
Q
:
Transistor
R
:
Resistor
PTH
:
Positive
characteristic
thermistor
MAIN
AMPLIFIER
CIRCUIT
(See
Figure
6)
This
main
amplifier
is
of
a
differential
1-stage
pure
comple-
mentary
circuit
and
besides
it
incorporates
Darlington
power
pack
(made
of
IC501
and
IC502)
in
which
the
drive
stage
and
power
stage
are
integrated
into
one
unit.
The
bias
circuit
is
incorporated
in
the
Darlington
pack
and
it
assures
a
more
stabilized
and
readjustment-free
function
of
the
amplifier.
Moreover,
this
circuit
scarcely
is
affected
by
the
power
voltage
variations
since
it
employs
a
current
regulator
circuit
for
the
common
emitter
power
source
of
the
differential
amplification
stage.
The
pre-drive
transistors
Q507
and
Q508
are
a
current
regula-
tor
circuit,
which
assures
a
higher
gain
and
a
lower
distortion.
To
the
bases
of
these
transistors
Q505
and
Q506
are
connected
C511,
C512,
R513
and
R514
and
thus
a
rise
time
of
Q505
and
Q506
is
delayed
so
that
there
will
be
no
shock
noises
at
the
speaker.
BMETER
CIRCUIT
(See
Figure
6
and
7)
With
this
meter
circuit,
output
signals
(from
the
pin
(4)
of
IC501
and
pin
(4)
of
IC502)
of
the
main
amplifier
are
con-
verted
into
DC
signals
to
undergo
logarithmic
amplification
and
thus
it
becomes
possible
to
drive
the
output
meters
MEI!
and
ME2.
The
AC
output
signals
of
the
main
amplifier
are
supplied
to
D603
and
D604
where
their
negative
components
are
removed.
Then
the
signals
undergo
logarithmic
amplification
through
D605
and
D606,
thus
driving
the
output
meters.
D601
and
D602
are
to
prevent
D603
and
D604
from
being
reverse-biased.
C601
and
C602
are
a
speed-up
capacitor
to
increase
response
speed
of
the
output
meters.
Note:
Hereunder
given
are
the
explanations
on
the
behavior
of
various
circuits;
main
amplifier
circuit,
meter
circuit,
electro-
nic
muting
circuit,
meter
circuit,
electronic
muting
circuit
and
equalizer
circuit.
In
which,
note
that
the
following
symbols
will
be
used
in
the
descriptions:
C
:
Capacitor
IC
:
Integrated
circuit
ME
:
Output
meter
Q505
,Q506
25A818
YL
1¢-501
RH-IXIOG6
AF
ZZ
SPEAKERS
;
SWITCH
1.$K
soosy
olosv
i.
es
(sw902h
isw9az)
iC-
502
RH-
XIOG6A
ZZ
Q507
,
0508
2SC
1628
YL
Figure
6
C603
0603
3.3/50V
eo
+
H
era
5
a
R605
V¥R6Or
}
ME
!
,
22K SKE
|
°
(7)
LEFT
0605
METER
151555
+
K60l
L_)
HEADPHONES
J39Ol
TM902
SPEAKER
1B)
K70B8
|
Figure
7

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