Fiddles -- prime requirements for the orchestra, you suspect (4)
I believe the answer is:
toys
'fiddles' is the definition.
(I know this)
'prime requirements for the orchestra you suspect' is the wordplay.
'prime requirements for' says to take the initial letters.
The initial letters of 'the orchestra you suspect' is 'TOYS'.
(Other definitions for toys that I've seen before include "Fiddles" , "dolls, for example" , "Things that provide amusement" , "Chihuahuas?" , "Matters of no importance" .)