Design for avtive hi fi sub help

[diydidi]

Hi All.
Busy building a Hifi sub. Enclosure unfortunately is ported, but it will do. Using 12" woofer. Just finished the power supply, amplifier and DC protect circuit.
I need a design/ schematic for a crossover/ preamp for it. Must have variable control for crossover freq and a gain control also a phase switch.
If anyone has a schematic or design they are willing to share, that would be great.

[soundguruman]

https://www.google.com/search?q=rane...h=825&dpr=1.25