well when i set up my brothers stereo and have the amp to the subs (500.1) set anywhere above 1/3 power the 2 12w3's make a weird popping sound. why would this happen? TIA

 

this is because you are turning the gain up too much. The gain is not a volume **** it is there to match the voltage between the amp and the deck. turn the gain down to where it is supposed to be and you won't clip the amp.

 

I agree. That popping is called clipping which is where your amp can no longer amplify the signal due to electrical limitations therefore causing it to "clip" off the top of the signal causing the sine wave to go flat. This will KILL your speakers if it is not fixed.

 

he's right, its clipping, and it will ruin the speakers and the amp. You need to equal the gain to the voltage that your radio pre-amps give out. Say your radio has 4Volt preamps, then match them with 4 volts on the amp. If you use it as a volume **** it will ruin your amp.