Classical music turncoat, admitted jazz fan (7)
I believe the answer is:
toccata
'classical music' is the definition.
'toccata' can be an answer for 'music' (toccata is a kind of music). I am not sure about the 'classical' bit.
'turncoat admitted jazz fan' is the wordplay.
'turncoat' becomes 'toca' (I can't justify this - if you can you should give a lot more credence to this answer).
'admitted' indicates putting letters inside.
'jazz fan' becomes 'cat' (slang term for a jazz fan).
'toca' placed around 'cat' is 'TOCCATA'.
Can you help me to learn more?
(Other definitions for toccata that I've seen before include "Series of musical runs and chords before a fugue" , "technical challenge" , "Flashy piece of music" , "Keyboard piece emphasising touch" , "Baroque musical piece" .)