Filter Design - BSS Audio FDS 360 User Manual

20.4 Filter Design

Reference should be made to Figure 20.1.
Section A: First Order Low Pass Filter.
This can be used in conjunction with that of section B, and an example plot is
shown in Figure 20.4.
The equation for the -3dB frequency point of this circuit is:
F = 1/(6.28 x R2 x Cx),
Note should be taken that R2 is factory fitter as 10k ohms. Inspection of the
circuit will show that it is also possible to change the gain of the filter block
at this point. The actual gain in dB is:
G(dB) = 20 x log(R2/R1)
It should also be noted that both R2 and R1 are factory fitted as 10k ohms, and
should the value of R2 be changed, this must be accounted for in the
calculation of Cx.
Design limits for both R1 and R2 are in the range of 2k to 100k ohms. There is
no restriction on the value of Cx, apart from physical space on the circuit
board.
where R is in ohms,
C is in Farads,
F is in Hz.
33