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SECTION
IV
THEORY
OF
OPERATION
4
.
1
GENERAL
This section provides
a
generalized description
of the 562
circuitry, and should be used
in
conjunction with
the
schematic
at
the end of the
manual
.
4.2
INPUT AMPLIFIER
The signal
is
applied
to
a
differential input amplifier
(IC
1,
sections
C
and D).
The input accepts either balanced or unbalanced
sources
(see
also Installation, Section 2.5).
Common mode rejec-
tion
is
factory adjusted with
R1 and is
typically better than
40 dB.
4.3
GAIN AMPLIFIER
IC 1A is a
variable gain amplifier providing -12
to +18 dB
of gain.
Thus
the
stage has
a
gain range
of 30 dB,
allowing
adjustment through
the
Model
562
from from -10 to +20
dB,
referenced
to
unity gain.
4.4
FEEDBACK SUPPRESSOR
There are five identical notch filter sections
in the
Model
562.
The filter type
is
"State Variable."
Each filter utilizes four
operational amplifiers which
are on
a
single
IC;
filter
#1
will
be
described
.
Frequency Selection
is
variable with
the
dual front sections
of R36
over
the
ranges from
60
to 600 Hz and 600 to 6000 Hz,
depending
on the
setting
of the
multiplier
switch.
The signal output of amplifier section D
(at
pin
14)
consti-
tutes
a
bandpass function with
the
center frequency selected
as
described previously.
The signal
is
180° out of
phase with
the
input signal.
To achieve
a
notch, some bandpass signal
is
mixed
with
the input signal ahead
of
the summing
amplifier
(see typical
attenuation curves
in
Section
VI).
Notch Depth
is
variable
from
0
dB to
20
dB
with
the third section (center shaft) of the poten-
tiometer R36
.
A loss of
approximately
0.8
dB
is
taken through each
filter section
for
a
total of
4
dB through the
5
sections.
4.5
ENDCUT FILTERS
IC 8A
and
IC 8B
and
associated components are
a
voltage
controlled
voltage source high pass
(low
frequency cutoff)
and low
pass (high frequency cutoff) filters respectively.
Both filters
are 12
dB/octave Butterworth types.
The high pass section has
4
dB
of
voltage gain; the low pass section
is
unity gain.
-
15
-
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