4-channel amplifiers ?
Video: Alpine KTP-445U Universal Power Pack Amplifier
Alpine's KTP-445U Power Pack is the easiest way to pump up the power of your in-dash receiver. It gives you a robust 45 watts RMS x 4 channels, so you can give your aftermarket speakers the power they need to sound your best. This amp installs inline with your receiver's wiring harness, so there's no need to run a wire to your battery. It's compact and fits behind many dashes.