I patched up a conventional drone, which I recorded while improvising.  The featured oscillators:  Synthesis Technology Cloud Generator (E340) and Modcan VCDO.  Each passes through a Mattson VCA with an envelope (Blacet EG2070 looping) and modulation from a MOTM-300 VCO.  No digital effects were used; only a pair of Blacet Time Machines patched through the effects loop of my studio mixer.