What an Amp Does
An electric amplifier (or simply "amp") is used, as its name suggests, to increase the amplitude of sound waves produced by a source, such as an electronic instrument. The frequency (or number of occurrences of a sound wave) is not changed, but the peak/crest ("height") of the sound wave is increased. The degree to which an amplifier increases a signal is known as its "gain."
Preamplifier
Many amplification systems include an element called a preamplifier (preamp), which is used to level out sound before it is finally amplified and produced through the amplifier's loudspeaker. In many cases, the signal coming into a preamplifier is barely audible (as the electrical signal from an electric guitar), and the preamplifier increases the signal to its line level, which is an intermediary amplification which decreases noise produced by the power amp, the next portion of the system. In instrumental amplification, the preamp is also the stage at which effects, such as reverb, are added to the sound.
Valve Power Amp
Valve power amps make use of vacuum tubes, which make use of electrodes in a vacuum to amplify an electric signal. That is, electrons are passed between the positive anode and the negative cathode. A heat difference between the anode and cathode is key to the operation of vacuum tubes, but the necessity of anode cooling means that they are relatively inefficient. Nevertheless, they are still considered to be the best option for radio broadcasting, and many musicians prefer tube amp systems for what might be described as their "warm" sound.
Transistor Power Amps
Transistor have by and large replaced vacuum tubes in electronic amplification. Transistors are semiconductors that, with the addition of an increased voltage, can put out a greater signal amplitude than was put in by controlling the signal as it travels between the terminals of the transistor.
Loudspeaker
The rest of the amplifier functions to increase the amplitude of the waves of the electrical signal. The loudspeaker turns this amplified electrical signal back into sound waves so that it is produced as audible sound. A loudspeaker is thus a type of transducer, transforming one form of energy to another (in this case, in the electroacoustic direction). This is accomplished via the vibrations of a pliant diaphragm, which is set into a basket. The two are attached by a wire in which an electromagnetic field is created (by the motion of current through it). The resulting motion of the wire and diaphragm produces sound out of the electric energy.
Tags: electrical signal, vacuum tubes, increase amplitude, increases signal, sound wave