Personal appeal — playing harmonicas not on! (8)
I believe the answer is:
charisma
'personal appeal' is the definition.
('charisma' can be a synonym of 'personal appeal')
'playing harmonicas not on' is the wordplay.
'playing' indicates an anagram.
'not' suggests deleting specific letters.
'harmonicas' with 'on' taken out is 'harmicas'.
'harmicas' with letters rearranged gives 'CHARISMA'.
(Other definitions for charisma that I've seen before include "Glamour" , "divine power" , "Capacity to inspire enthusiasm" , "powerful influence" , "Personal magnetism, great charm" .)