A keyboard instrument I used with the top off but sorted out (9)
I believe the answer is:
organised
'sorted out' is the definition.
'organised' can be an answer for 'sorted' ('sorted'->'organized' is in my internal thesaurus and 'ize'->'ise'). I am unsure of the 'out' bit.
'a keyboard instrument i used with the top off' is the wordplay.
'a keyboard instrument' becomes 'organ' (I've seen this in another clue).
'used with' is a charade indicator (letters next to each other).
'the top off' becomes 'sed' (I can't explain this - if you can you should give a lot more credence to this answer).
'organ'+'i'+'sed'='ORGANISED'
'but' acts as a link.
Can you help me to learn more?
(Other definitions for organised that I've seen before include "Efficient" , "Methodical" , "Set up,mobilised" , "fixed up" , "Put in order" .)