are devices that increase or amplifiy
a small electrical signal (that comes from an instrument pickup) so that the signal is large enough to operate a speaker. Amplifier heads are in separate cabinets from the speakers they drive. The wire connections between the amplifier and speakers are temporary and external to the cabinet. Stand-alone amplifier heads generally have larger power ratings than combo amps (in which the amp and speaker share an enclosure and the wire connections are internal and temporary).