0 - 180 var. phase control for sub xover

what topology will give you a 0-180^ variable phase control? anyone have any schematics?
A subwoofer plate amp that I have the schematic for is like this.

1. Draw an OP amp.

2. The signal is connected to the - input through a 1K resistor. Also connected to the - input is feedback from the output through a 910 ohm resistor.

3. The signal is also connected to the + input, through a 1K resistor and a 0.022uf capacitor. Also connected to the + input is a 1 meg pot and an inductor (unknown value) in series and going to ground. Phase is adjusted using the Pot.

Go figure.