5. Amplifiers
The amplifier section is both the control centre and the workhorse of your hi-fi system. The control centre is called the preamplifier. This is where all the sources you may have are connected and selected. It is also where the gates are opened as far as volume is concerned. The workhorse is the power amplifier which provides all the juice to amplify the source's signal. It also sets up, and gives breadth and depth to the soundstage.
You can find the amplifier section in two formations: as separate preamplifier and power amplifier components; or as an integrated amplifier which combines both into a single box. There are advantages to both options and, once again, your own criteria will dictate which way you go.
As stated before, the functions needed of an amplifier are split in two—to control the incoming signal, and to boost them to the level needed to drive the speakers. Another function of preamplifiers is tone control and audio filters. Purists tend to deride tone controls, but there is still a need for them when deficiencies in equipment, room acoustics or program material would otherwise make listening less pleasant. If all things were perfect there would be no need, but alas, 'tis an imperfect world we live in…
Yet another issue to be mindful of is the interactive relationship the amplifier has with the speakers. Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing." In other words, the speaker produces sound waves that are not part of the original signal.
Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope. When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its suspension. So that nice, snappy kick drum turns into a booming throb. Fortunately, a power amplifier can exert control over the loudspeaker and reduce ringing.
Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor. As you might suspect, damping factor is most important at low frequencies, say 10 Hz to 400Hz. High damping factor equals tight bass. In short, the loudspeaker damps itself through the amplifier output circuitry.