I have made calculations for a 4th order State variable active filter. The filter can be configured either as Linkwitz-Riley or Butterworth.
The nice thing about a State Variable active filter is that the same circuit has complementary outputs for Low pass and High Pass. The cutoff frequency is set by four identical RC pairs. Changing the RC pairs changes the frequency for both Low-pass and High-pass outputs, Gain can be set within a wide range. Unlike Sallen-Key implementations which need separate High-pass and Low-pass circuits with matching RC combinations and constrained gain options.
The attached report describes the analysis, calculation, simulation and measurement on a real circuit.
The nice thing about a State Variable active filter is that the same circuit has complementary outputs for Low pass and High Pass. The cutoff frequency is set by four identical RC pairs. Changing the RC pairs changes the frequency for both Low-pass and High-pass outputs, Gain can be set within a wide range. Unlike Sallen-Key implementations which need separate High-pass and Low-pass circuits with matching RC combinations and constrained gain options.
The attached report describes the analysis, calculation, simulation and measurement on a real circuit.
Nice writeup, thanks!
The old AudioControl RS series subwoofer crossover/equalizers used state variable just as you describe. They weren't "high-end", but very good, very functional units that worked well. Mine is still in-use 25+ years on.
The old AudioControl RS series subwoofer crossover/equalizers used state variable just as you describe. They weren't "high-end", but very good, very functional units that worked well. Mine is still in-use 25+ years on.
This is great work jlinkels. I've taken the liberty of putting it into LTSpice for those of us not familiar with Qucs-S who want to play with it. It seems to work ok, please let me know if there are any corrections to be made. Sim file attached.
