First violin starts the cassette tape (6)
I believe the answer is:
leader
'cassette tape' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'first violin starts' is the wordplay.
'first' becomes 'lead' (lead can mean leading or primary).
'violin starts' becomes 'er' (I can't explain this - if you can you should give a lot more credence to this answer).
'lead'+'er'='LEADER'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for leader that I've seen before include "Chief or front man" , "Guide; editorial" , "Opinion piece; boss" , "Superior" , "Guide, commander" .)