Source components like CD players, DVD players, tuners, and turntables do not produce enough volume to drive speakers directly. Two additional stages are needed before the signal gets to your speakers; a control stage and an amplification stage. See "players".
Preamplifiers provide control. Controls mean knobs and buttons. Preamps have a volume knob at a minimum, and usually have knobs or buttons to select from among the several sources you may have connected. They usually also have a balance control and may have tone controls and even a remote control to perform all of the above. The volume from a preamp is still not strong enough to drive speakers directly.
Amplifiers amplify the signal from the preamp and output a signal strong enough to drive speakers. Amps are the engine or the muscle that drives your speakers. This is where the volume comes from. However, amps have no control over themselves and have no common sense. Without a preamp to provide control they’ll usually blow themselves and the speakers up in a minute. Besides the preamp for control, you need one amp for volume to each speaker. Stereo amps or two channel amps have two amps in one package. Multi channel amps have, well, multiple amps in one package. You can get three, four, five, and sometimes even seven channel amps. The fanciest ones though, are just one channel! They’re called monoblock amps. It just means you need another amp (and more money) for each speaker. They’re sweet.
Integrated Amplifiers are a preamp and a stereo amp in one package. Connect a CD player and speakers and you’ve got tunes. ‘Nuff said.
Receivers combine a tuner, a preamp, and amplifiers into one box. Stereo receivers only have two amps in there and usually only have inputs for audio only sources like CD players and turntables. Audio/Video (A/V) receivers have more amplifiers inside, additional connections for DVD players and such, outputs for five or more speakers, and additional processing circuitry for all the surround sound stuff. Some but not all A/V receivers also allow you to connect the video signals from video sources and then output the correct signal to your TV. They sound ok, I guess.
Why separate components? Since technology has advanced soooooo far that we can get all that stuff and more into a slick A/V receiver, why on God’s green earth would someone want a separate component for each job. Simple; it sounds better. Always? No, not if the seperates aren’t better than the receiver was to begin with OR if the seperates do not match well with each other. When separates are done right though, they can be way more musical and realistic sounding. A piano sounds far more like a real piano in your room. A really good system can come quite close to recreating an entire orchestra, hall and all, right in your living room. The musical performance of the seperates we have will smoke any receiver on the planet, hands down. Sound too bold? Come see us and we’ll prove it in ten minutes.