Golden balls, though that's not all (4)
I believe the answer is:
orbs
'golden balls' is the definition.
'orbs' can be an answer for 'balls' ('orb' can be a synonym of 'ball'). I'm unsure of the 'golden' bit.
'that's not all' is the wordplay.
'that's not' becomes 'o' (I've seen this in other clues).
'all' becomes 'rbs' (I can't explain this - if you can you should believe this answer much more).
'o'+'rbs'='ORBS'
'though' is the link.
Can you help me to learn more?
(Other definitions for orbs that I've seen before include "Round objects" , "circles" , "Eyeballs" , "Jewelled spheres" , "Poetic eyes, bros" .)