Akai AT-2650

VIL
OPERATING
PRINCIPLES
OF
FM
NOISE
IC
LA2100
used
in
this
model
is
a
monolithic
IC
for
FM
noise
canceller
use.
Situated
between
the
FM
detector
and
the
stereo
demodulator,
this
circuit
features
effective
elimination
of
pulsive
external
noise
such
as
engine
noise.
CANCELLER
CIRCUIT
(1)
(2)
Det
Vin
'
(GATE)
1
|
|
H(NOISE)
|
I
!
I
(SIGNAL)
|
|
we
ON
=
+
za
Fig.
19
Basic
circuit
for
pulse
noise
suppression
and
wave
forms
1.
BASIC
CIRCUIT
FOR
PULSE
NOISE
SUPPRESSION
The
composition
of
LA2100
is
made
up
of
a
gate
circuit
and
a
holding
condenser
to
eliminate
pulse
noise.
When
the
gate
is
closed
as
in
Fig.
19(1),
condenser
Co
is
driven
by
a
low
impedance
(emitter
follower
TRI)
and
therefore
the
output
signal
is
the
same
as
the
Vin
input.
When
pulse
noise
enters,
the
gate
opens
immediately,
and
condenser
Co
maintains
the
signal
level
prior
to
noise
input.
When
the
noise
stops,
the
gate
closes
and
the
wave
form
returns
to
normal.
The
output
wave
form
Vout
becomes
similar
to
the
wave
form
of
Fig.
19(3).
Interms
of
noise
alone,
it
means
that
the
noise
(2)
is
suppressed
as
in
(3).
2.
OPERATION
PRINCIPLE
WITH
STEREO
SIGNALS
When
the
aforementioned
circuit
is
used
on
the
stere
0
signals,
the
pilot
signal
is
cut
out
while
the
gate
is
open
and
distorts
the
stereo
composite
signal
to
generate
irritating
noise.
To
prevent
this
distortion,
during
the
time
gate
is
open
a
19
kHz
sine
wave
of
the
same
amplitude
and
phase
as
that
of
the
plot
signal
is
generated
from
the
pilot
signal
generating
circuit
(19
kHz
sine
wave
generating
circuit).
Thi
is
added
to
the
holding
condenser
Fig.
19(1)
eleciric
potential
while
the
gate
is
open
and
compensit
€s
the
pilot
signal.
i
15