Did you ever find the need for a variable frequency low cut filter?
If so, this will give you a slope of 12 db per octace below the selected
cutoff frequency. There is even an adjustment for the "Q" of the filter.
Here is the schematic
![](51199019.jpg)
![](51199018.jpg)
![](51199020.jpg)
Parts list
C1 .1uf
C2 .1uf
R1 47k
R2 4.7k
R3 4.7k
R4 10k
R5 5.6k
U1, U2, U3 are 3 sections of a quad op amp
VR1, VR2 Dual 100k potentiometer from radio shack
Specs:
Cutoff freq 18 hz to 350 hz
Q range 0.5 to 3.0
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