Sound boosters (4)
I believe the answer is:
amps
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sound boosters</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for amps that I've seen before include "Units of electrical power" , "concert gear" , "Spam (anag)" , "Current measures" , "'Units of electric current, in short (4)'" .)