              3-way 4th Order Active Crossovers for Car Audio

These crossovers are meant to be used with my amps in my car audio system.
They derive +/-15V power from an extra winding on the car amp's power
supply transformer. Aside from their power source they are general purpose
crossovers. Note that the low frequency output is DC coupled from the input
- you can only do this if you have an input source and op-amps which create
negligible offset (or it's OK if your amp is AC coupled). I designed my
filters to have a 4th order Butterworth characteristic with crossover
points at 100Hz and 3kHz. All of my filter resistors and capacitors are
mounted on DIP headers for easy removal to change the crossover
frequencies. The current component values I'm using are as follows:

                  Filter           R1    R2   C1    C2

                  3kHz HP Stage 1  4.87k 5.76k10nF  10nF

                  3kHz HP Stage 2  2.05k 13.7k10nF  10nF

                  3kHz LP Stage 1  8.87k 31.6k10nF  1nF

                  3kHz LP Stage 2  3.92k 10.2k10nF  6.8nF

                  100Hz HP Stage 1 14.7k 17.4k100nF 100nF

                  100Hz HP Stage 2 6.04k 41.2k100nF 100nF

                  100Hz LP Stage 1 7.87k 21.5k150nF 100nF

                  100Hz LP Stage 2 26.7k 95.3k100nF 100nF

