Jack in bar, old music-maker (5)
I believe the answer is:
banjo
'music-maker' is the definition.
(banjo is a kind of musical instrument)
'jack in bar old' is the wordplay.
'jack' becomes 'J' (playing card abbreviation).
'in' is an insertion indicator.
'bar' becomes 'ban' (I've seen this before).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ban'+'o'='bano'
'j' placed inside 'bano' is 'BANJO'.
(Other definitions for banjo that I've seen before include "Bluegrass instrument?" , "Softly (music)" , "Guitar-like instrument" , "No jab (anag.)" , "Stringed instrument of the guitar family" .)