Sony STR-S5L - Circuit Descriptions; Sound Enhancer Circuit

I
I
STR-S5
SECTION
1
OUTLINE
1-1.
CIRCUIT
DESCRIPTION
ISOUND
ENHANCERI
Figure
A
shows
an
amplifier
from
the
operation
amp.
Its
gain
is
determined
by
NF
resistors (Rl,
R2)
and
the
gain
of
the
operation
amp.
Therefore,
if
frequency
response
is
given
to Rl
and
R2,
the
amp
response
can be
freely
formed.
The
sound
enhancer
circuit
of
this
model
makes
3 kinds
of responses
by
inserting
a resonance
circuit
parallel
to
R2
by
a
switch.
Figure
B
shows
the
resonance
circuit
diagram.
The
section
within
the dotted
line
performs
the
same
task
as
a coil
and,
with
C609,
forms
the
series
reso_
nance
circuit.
Following
is the
explanation
of
the
section
of
the
circuit
within
the dotted
line.
In
Figure
C,
by
raising
the
voltage
at
(S,
charg_
ing
current
i2
flows
to
C2 and
i3
also
flow..
When
i3
flows,
the
potential
at@rises,
so the
potential
at
@
is also
pushed
up
by
this.
At this
time
the
current
i1
flowing
from
the
power
applied
to
@
is
very
small,
and
i2
is
supplied
almost
totally
as
a iesult
of
the
rise
in voltage
at@.
However,
the
charging
current
i2 decreases
as
time
elapses.
Consequently,
since
potentid
at
@
aho
drops,
i1 becomes
ia
and
increases
as
time
elapses.
By
lowering
the
potential
at
@,
the directions
of
current
and voltage
reverse
and
thus
operation
also
reverses.
Therefore,
by
applying
ac
to
point
@
in tH,
circuit,
the
phase
of i1
lags
the
voltage
by
90o.
This
is because
this
circuit
performs
the
same
job
as
a coil.
Q
is determined
by
the
hfe,
etc.,
of R2,
R3,
R4,
Ql.
This circuit
is
called
active
filter,
and
is often
used
in
graphic
equalizers.
Fis.
C
Fig.
A
L___
Fig.
B