An electronic device strengthening the electrical signal from a pick-up on an electric guitar, bass guitar, or an acoustic guitar in order to produce sound through loudspeakers. There are two main forms of guitar amplifiers:

head - a standalone wood or metal cabinet consisting only of the power amplifier (and pre-amplifier) circuits, requiring the use of a separate speaker cabinet; (Presented on the left side of the picture; head is the upper part of the construction, the lower part is a speakers cabinet)

combo - an amplifier including both the amplifier's circuits and one or more speakers in a wooden cabinet. (Presented on the left side of the picture)

Amplifiers differ in terms of their sizes and power. A size of an amplifier is usually determined by the size and number of loudspeakers (e.g. 2x 12").