Electronics > Projects, Designs, and Technical Stuff
Modified second-order low pass filter (third order?)
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Conrad Hoffman:
I did this a while back- http://www.conradhoffman.com/4_pole_LP.zip

Everybody hates it because some variations will be very component sensitive, but it kills noise like nobodies business. I've had little trouble with the several I've built.
Wimberleytech:

--- Quote from: Conrad Hoffman on February 03, 2020, 09:57:00 pm ---I did this a while back- http://www.conradhoffman.com/4_pole_LP.zip

Everybody hates it because some variations will be very component sensitive, but it kills noise like nobodies business. I've had little trouble with the several I've built.

--- End quote ---

I ran your program (for fun) and then checked it in LTSPice.  Nice.

Does the program iterate to a solution, or is it solving a set of design equations?
Conrad Hoffman:
The program is a port of a Fortran program found in an old Burr-Brown book. When you get to 4th order the math becomes annoying. Can't remember, but I think it's more of a brute force numerical solution to a set of design equations. On a fast machine you can iterate a mighty long ways and nobody will notice! Of course, once you calculate the prototype for a given type, you don't need the program at all. Just apply the usual scaling.
Wimberleytech:

--- Quote from: Conrad Hoffman on February 04, 2020, 12:51:50 am ---The program is a port of a Fortran program found in an old Burr-Brown book. When you get to 4th order the math becomes annoying. Can't remember, but I think it's more of a brute force numerical solution to a set of design equations. On a fast machine you can iterate a mighty long ways and nobody will notice! Of course, once you calculate the prototype for a given type, you don't need the program at all. Just apply the usual scaling.

--- End quote ---

That's what I figured.  Thanks.
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