I want to replace the head unit in my car so that I can play cds or hook my ipod in. Eventually i'd like to get a sub for my car. Would I be able to connect the amplifier for the sub to anyone head unit I pick up from best buy? I don't want to replace the radio only to find out that I can't add a sub without a better head unit.
look for a headunit with preamp outputs, some will only have 1 set for the front or 2 sets for front and rear, the better ones will have outputs for front, rear and subs. If not you can always use something called a LOC or line output converter. Also look at the "output voltage" on the stereo, the majority of them will have 4 volt and the cheezier ones will have 2 or 2.5 volts.
