Original: In standard Dutch, based on the dialect of Holland, it is, with a voiceless V/O. However, though Van Gogh's parents were from Holland, he grew up in Brabant and used Brabant dialect in his writing; it is therefore likely that he himself pronounced his name with a Brabant accent:, with a voiced V and palatalized G and gh.
Simplified: (His last name in Dutch is pronounced to rhyme with Scottish "loch".