Ordinary pop group in sassy musical headgear (5-3)

I believe the answer is:

opera-hat

'musical headgear' is the definition.

'ordinary pop group in sassy' is the wordplay.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'pop group' becomes 'aha'.
'in' indicates putting letters inside.
'sassy' becomes 'pert'.
'aha' going within 'pert' is 'perahat'.
'o'+'perahat'='OPERA-HAT'

I've seen this clue in The Independent.

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