Crown PSA-2 - Circuit Theory and Modifications; Filter Frequency Alterations

7.10 PSA-2 HI/LO Pass Filter
Frequency Alterations
In order to alter the roll-off frequency of the HI/ LO pass
filters, it is necessary to change several components
located on the Filter Module (within the Balanced Input
Module). A portion of the Balanced Input Module
schematic and filter board layout diagram are duplicated
below to aid in familiarity with the component parts
referred to in conversion formulas.
Step 1: Remove the Balanced Input Module from the
rear of the unit.
Step 2: Remove the shield board by gently crimping
together each of the two retaining clips; lift board
upward.
Step 3: Remove the filter board by gently crimping
together the one retaining clip while simultaneously
lifting board upward.
Step 4: Perform the following calculations which will
determine the value of C107, C108, C109, C207, C208,
C209, R102, R103, R104, R202, R203 and R204.
be |
By) 42337
ind
R108 clos
eee
eS
Bl uss RIO
Oly" ‘cos
C104
a ae F-5v
—) +d]
lev
1057 3 6
Ri04
D 4
Fig. 7.27 Filter Board Schematic
7-21
R207
Component changes for various
highpass and lowpass cutoff frequencies
1. ©103, 203, 104, 204, 105, and 205 all equal C*
2. R107, 207, 108, 208, 109, and 209 all equal R*
3. R* and C* are chosen according to the following general
limitations:
‘s))
{
a)
1K<
R*<
330K
(increasing
R’
value
gives
increased
noise)
b)
R102,
202>2K
c)
R104,
204<1M
4.
With
valid
values
of
R*
and
C*,
the
other
resistor
and
capacitor
values
are
chosen
according
to
the
following
formulas:
7184
R102,
202-
ae
2820
Sil
R103,
203-
HO
atct
vg
R104,
204=
anes
R102—
ad
;
coe
—
YJ
>
107,
207-
_1.392
2rfR®
C108,
208-
3.546
2nf,R*
€109,
209-
_.2024
2nf
R*
when
fn
=
highpass
cuttoff
when
fi
=
lowpass
cuttoff
5.
For
values
shown
in
schematic
fn
=
SOHz
and
fi
=
15KHz
sy)
4
ee
a]
1
'
Riu
cu
200K
Oatu
Sane
;
R
102
a7
!
'
'
1
1
1
!
'
1
1
a
Fig.
7.28
Filter
Board
Component
Layout
)
a)