Idiot taking daughter into Birmingham to get instrument (4,4)
I believe the answer is:
bass drum
'instrument' is the definition.
(bass drum is a kind of instrument)
'idiot taking daughter into birmingham' is the wordplay.
'idiot' becomes 'ass' (I've seen this before**).
'taking' means one lot of letters go next to another.
'daughter' becomes 'd'.
'into' indicates putting letters inside.
'birmingham' becomes 'brum' (I've seen this before).
'ass'+'d'='assd'
'assd' put into 'brum' is 'BASS DRUM'.
'to get' acts as a link.
(Other definitions for bass drum that I've seen before include "Big percussion instrument" , "Booming percussion instrument" , "Deep instrument" , "Large percussion instrument" , "musical instrument" .)