Turner inclined to keep soprano in prison (7)
I believe the answer is:
capstan
'turner' is the definition.
(turning or revolving machine part)
'inclined to keep soprano in prison' is the wordplay.
'inclined' becomes 'apt' ('apt' can be similar in meaning to 'inclined'**).
'to keep' is an insertion indicator.
'soprano' becomes 's' (musical abbreviation).
'in' indicates putting letters inside.
'prison' becomes 'can' (the can is American slang for prison).
'apt' placed around 's' is 'apst'.
'apst' inserted inside 'can' is 'CAPSTAN'.
(Other definitions for capstan that I've seen before include "One winds up" , "Apparatus to wind cable" , "Device winding in rope" , "Dockside rope winder" , "Cylinder for winding ropes/cables" .)