I noticed that Nelson Pass has adapted the filters that are used in the Mini DSP used on the Linkwitz LX-Mini. He has developed an active filter that uses JFETS. I read that he used Micro-Cap that has an active filter designer built in.
I have bought a Mini DSP and eventually would like to transfer the filter characteristic over to an analogue active filter.
What are the steps needed to do this? Is there any reference material I can study to make this possible? I have an Electronics background, so I'm willing to give it a try. Any help appreciated. Thanks.
David.
I have bought a Mini DSP and eventually would like to transfer the filter characteristic over to an analogue active filter.
What are the steps needed to do this? Is there any reference material I can study to make this possible? I have an Electronics background, so I'm willing to give it a try. Any help appreciated. Thanks.
David.
Mapping between digital and analog filter designs is done using the bilinear Z-transform.
This maps the positions of poles and zeroes between s-plane (continuous) and z-plane (discrete).
Bilinear transform - Wikipedia
There is literally vast amounts of reference material on this, there are hundreds of books on DSP out there, and most of them will cover this fundamental stuff.
Not sure JFETs are a good choice for an analog filter though, pretty ropey performance compared to BJTs and opamps as followers for a Sallen / Key stage.
This maps the positions of poles and zeroes between s-plane (continuous) and z-plane (discrete).
Bilinear transform - Wikipedia
There is literally vast amounts of reference material on this, there are hundreds of books on DSP out there, and most of them will cover this fundamental stuff.
Not sure JFETs are a good choice for an analog filter though, pretty ropey performance compared to BJTs and opamps as followers for a Sallen / Key stage.
In case your are familiar with the various filter gainbloc plus relevant RC network topologies (not onlt HP/LP, but also notch/peak/shelf) there might be a more DIY oriented way.
In case you have the transfer function of the complete filter in .txt or .frd format, you might use that as a so called "Target function" in Vituixcad by importing that curve into Vituixcad. You then create your own suitable filter blocks with opamps and RC networks (drag n drop that is) , and optimize the RC values with the aid of the Vituixcad optimizer. A somewhat steep learning curve for the inexperienced, but a piece of cake once you have gathered a bit of experience in using Vituixcad.
Simple textbook topologies are not going to work in most of the cases: you quickly will find you most likely will need notches and peaks (gyrator circuits) and shelves to properly mimic non-standard transfer functions.
In case you have the transfer function of the complete filter in .txt or .frd format, you might use that as a so called "Target function" in Vituixcad by importing that curve into Vituixcad. You then create your own suitable filter blocks with opamps and RC networks (drag n drop that is) , and optimize the RC values with the aid of the Vituixcad optimizer. A somewhat steep learning curve for the inexperienced, but a piece of cake once you have gathered a bit of experience in using Vituixcad.
Simple textbook topologies are not going to work in most of the cases: you quickly will find you most likely will need notches and peaks (gyrator circuits) and shelves to properly mimic non-standard transfer functions.
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