Sound boosters from Hampstead (4)
I believe the answer is:
amps
'sound boosters' is the definition.
(I've seen this in another clue)
'from hampstead' is the wordplay.
'from' says the answer is hidden in the clue.
'AMPS' can be found hidden inside 'hampstead'.
(Other definitions for amps that I've seen before include "concert gear" , "Units of electrical power" , "Current measures" , "Basic units of electric current" , "'Units of electric current, in short (4)'" .)