Opera composer uses percussion instrument in one (7)
I believe the answer is:
bellini
'opera composer' is the definition.
(I've seen this before)
'instrument in one' is the wordplay.
'instrument' becomes 'bell' (bell is a kind of instrument**).
'one' becomes 'i' (Roman numeral).
'bell'+'in'+'i'='BELLINI'
'uses percussion' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for bellini that I've seen before include "Peach juice cocktail" , "Cocktail; composer of opera Norma" , "Norma, I Puritani composer" , "He made a lot of notes" , "Italian opera composer (Norma)" .)