Right...the VCA has to be something which doesn't switch off when you get the negative-voltage parts of the AM cycle. Have a look at: http://electronicmusic.wikia.com/wiki/Four_quadrant where the VCA-as-ringmod thing is explained. My bet is that Nyle's output VCA on the Synthacon I had was capable of working in this four-quadrant mode with VCO3's output, allowing for the ring-like results. Anyway, even in two-quadrant modality, you're going to get this half-waved dirty sound, which in of itself could be useful.

AF = yes, audio frequency. Old habit from way too much radio experience.