It is pulsewidth modulation with a fast sine LFO plus the ultrasaw, with a fast setting, plus a sinewave sub one octave down.
The combination of heavy modulated pulse and saw together gives this interesting fat texture which is still quite smooth, yet a bit metallic. The osc levels were very low, like one quarter of the available volume. The brute factor was zero. In this way I managed to make it sound fat, yet quite smooth for what it is. The filter envelope part is pretty obvious I think.
