First violins start the cassette tapes (7)
I believe the answer is:
leaders
'cassette tapes' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe you can see a link between them that I don't see?
'first violins start' is the wordplay.
'first' becomes 'lead' (lead can mean leading or primary).
'violins start' becomes 'ers' (I am not sure about this - if you are sure you should believe this answer much more).
'lead'+'ers'='LEADERS'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for leaders that I've seen before include "They take the initiative and direct others" , "Top people" , "newspaper articles" , "Bosses" , "People to follow" .)