I have a 225watt Rockford Fosgate amp and I'm looking for a subwoofer. I was looking at one JL Audio 12W0 4ohm sub with a peak power of 125watts. Can I use this 125watt sub with my amp or will I blow the sub?

 

You can use whatever you want with your amp, and as long as the gain is adjusted right, you won't blow it out. The general process for setting up the gain is to connect just one amp at a time, put your head unit on 90% or so of volume, turn up the gain until you hear the first bit of distortion, and then turn it back down a bit.

 

You will be fine with that amp/sub setup. Just adjust the gain right as Botos said before. The max you should ever set the gain at is 75%, any higher then that, you will have a lot more distortion. The JL subs are very durable, they can handle a lot of power, they are all underrated specs.

 

Exactly which amp is it?

 

The sub is a RF-2.9x amp which is not sold anymore. I got it for $50 American.