Right then young Mac, first we need to understand what an "Amp" is doing. When a note or a chord is played on an electric guitar it is picked up by the.... pickup. You have no doubt heard the result of a guitar that is not equipped with an acoustic body cavity (acoustic guitars are) and agree that it is zilch. Now when the guitar is plugged in, ie powered, the pick up converts the strings almost inaudible sound waves into electrical impulses. These used to be analogue but are increasingly digital. Now the feed from the guitar is fed to what is commonly called an amp. The "amp" has 3 basic components. First the pre amp. This takes the very weak signal from the guitar pick up and enlarges it or shall we say pre amplifies it. This is important. It must not distort or allow spurious electronic "white" noise to enter the signal stream but must enlarge the signal enough to enable it to drive the main amplifier circuit which will in turn drive the speakers. Because the main amp drivers are basically a muscle output they rely on very clean input from the pre amp circuit. Now as you can by now imagine the wealthy or top end users of such equipment have needs well beyond the everyday requirements of most people and can afford to split these stages down into a dedicated pre amp, output amp and separate speakers for the massive audio levels that they require. I myself was astonished at a recent Stone Roses gig at thee size of what looked like tower mounted ceramic speakers, and wondered what the hell was going on between guitar pickup, microphone and re transmitted sound. Keep on enjoying your music.