According to the Longman Pronunciation Dictionary, the strong form is pronounced as (British) / (US), whereas the weak form is pronounced as . How is the informal short form (sometimes written as “O”) pronounced . There is no mentioning of any exceptions, suggesting that the of in “of course” (cf. Ref. Other answers and comments) is pronounced in the same way and that is not the case with f. Audio files can be found here. “of” is a rare exception of a word where f is pronounced like v. “F has f, as it

defines itself, so the definition is not exactly like that.”