Guitar Amplifier - Structure

Structure

Amplifiers consist of one or more circuit stages which have unique responsibilities in the modification of the input signal. The power amplifier or output stage produces a high current signal to drive a speaker to produce sound. This means that the signal does not really increase in amplitude, but it has a higher energy content. One or more preamplifier stages precede the power amplifier stage. The preamplifier is a voltage amplifier that amplifies the guitar signal to a level that can drive the power stage: the signal is made larger, but without significantly increasing its energy content. There may be one or more tone stages which affect the character of the guitar signal: before the preamp stage (as in the case of guitar pedals), in between the preamp and power stages (as in the cases of effects loop or many dedicated amplifier tone circuits), in between multiple stacked preamp stages, or in feedback loops from a post-preamp signal to an earlier pre-preamp signal (as in the case of presence modifier circuits). The tone stages may also have electronic effects such as equalization, compression, distortion, chorus, or reverb. Amplifiers may use vacuum tubes (in Britain they are called valves), or solid-state (transistor) devices, or both.

There are two configurations of guitar amplifiers: combination ("combo") amplifiers, which include an amplifier and anywhere from one to four speakers in a wooden cabinet; and the standalone amplifier (often called a "head" or "amp head"), which does not include a speaker, but rather passes the signal to a speaker cabinet or "cab". Guitar amplifiers range in price and quality from small, low-powered practice amplifiers, designed for students, which sell for less than US$50, to expensive amplifiers which are custom-made for professional musicians and can cost thousands of dollars.