Sentimentality effected with each brainwave (4,4)

I believe the answer is:

good idea

'brainwave' is the definition.
(brainwave can mean an idea)

'sentimentality effected with each' is the wordplay.
'sentimentality' becomes 'goo' (informal term for sentimentality).
'effected' becomes 'did' ('do' can be a synonym of 'effect').
'with' means one lot of letters go next to another.
'each' becomes 'ea' (abbreviation).
'goo'+'did'+'ea'='GOOD IDEA'

I've seen this clue in The Guardian.

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