How do I hook up a passive sub to a stereo?

[Matthew Lucas]

Do i need any other amps?

My stereo is a philips fw-p78

The sub is a durabrand sw-sp1

 

[americanaudiophile]

You would have to use something like this
http://www.parts-express.com/subwoofer-crossover-8-ohm-150-hz-200w--260-220
connecting the front left and right speakers and sub. You won't have a way to set the levels to match and the result might be worse than without.
A self powered subwoofer would work much better.