Amplifiers are needed if you want speakers, rather than just listening throught headphones. The basic amplifier, will have several analogue phono inputs, from several sources such as a CD player, minidisc deck, or turntable deck. The turntable deck's output will be of very low volume and needs to plugged into a specially labelled "PHONO" input on an amp, which is amplified twice. A basic amplifier will have two amplified out connectors for two speakers. More expensive amplifiers, may have four, two for left and two for right.
If you want to benefit from the multi-channel sound from DVD, you've need a home cinema amp. These have a front left and right, centre, rear left and right amplified outputs. Some accept a digital optical or coaxial signal from a DVD player, which they then decode. Other amps, need to be connected to dedicated decoders or DVD players with built in decoders. Some amps have decoders and can accept output from decoders. At the moment speakers cannot reproduce sound from digital signals.

Some specialist amps, can only take inputs from only one source. They require you to connect a preamp to them. All your sources then need to be connected to the preamp. Make sure your preamp or amp, has enough inputs for any components you wish to buy in the future.

Buying Amps. Professional amps for DJs are slightly different to ordinary amps. Firstly, most fit into a rack, like most DJ equipment. They are not as user friendly because they often have little or no controls. Some (like the one to the left), have decibel meter gauges to give you an idea of the sound level. This is useful to make sure that they are not to loud. Also they tend to be heavy duty machines with special features like cooling fans, to increase their life. They are very efficient machines. For real monster sound you can use several at the same time!

Outputs. However, for most people, a pro amp is not worth it. More important considerations for the ordinary buyer are features such as usability or price!

Here are all the outputs on a Yamaha RX795. Let's start from the right. You've got the power cable to the mains. Then two power outputs for two hi-fi seperates such as a CD player. Then you've got six outputs from the built in decoder. This would be useful if you wanted to connect another amp in series. Then continue to the left and their are six terminals to connect to rear speakers and a centre speaker in a multi channel setup. Below them are the A and B amplified speaker outputs for connecting upto four speakers for the front left and right channels. Continue along the bottom to the left and there are all the phono inputs and outputs for a VCR, TV, DVD, TAPE and TURNTABLE. You can connect other components to these, but the PHONO labelled input is reserved for a Turntable. Above that are video inputs. These are needed to overlay the amps user interface. These are not important.

Now at the top left there's an antenna in signal, because this amp has a built in tuner to receive radio. No going to the left you'll find that their are several optical digital inputs and a coaxial input (orange). Connecting a CD player to a digital input, will mean that the amps DAC is going to be used rather than the CD player's! Then further right, there are six inputs to be plugged in from an external decoder. One of the few things this amp does not have is any digital outputs. However, it has virtually everything else.