Bit of concert equipment (3)
I believe the answer is:
amp
'bit of concert equipment' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for amp that I've seen before include "A flow of one coulomb per second" , "In short, unit for measuring electric current" , "sound is increased by this" , "Sound-boosting piece of equipment (abbr)" , "measure of power" .)