Back goes after picking up an amplifier (7,3)
I believe the answer is:
hearing aid
'an amplifier' is the definition.
(thesaurus)
'back goes after picking up' is the wordplay.
'back' becomes 'aid' (I've seen this in another clue).
'goes after' is a charade indicator (letters next to each other).
'picking up' becomes 'hearing' (hearing is a kind of picking up).
'aid' after 'hearing' is 'HEARING-AID'.
(Other definitions for hearing aid that I've seen before include "asset in court?" , "Amplifier for ear" , "Help for the partially deaf" , "Ear trumpet" , "Earpiece" .)