I saw your question while browsing through this thread. Yes, I have some info about Charlemagne’s drone machine. A few years ago I restored it for a concert of his.
It consists of two identical panels, each with a Buchla 295 octave filter bank, some mixers and four oscillators designed by Serge Tcherepnin. Every oscillator outputs a sine-like waveform, a triangle, a pulse and a sawtooth. There’s a pot for the pulse-width, a 10-turn frequency pot and a 4 position switch to set the scale of the frequency pot. No voltage control.
A photo of the front panel:
Bottom right: the controls of two of the four oscillators
Above that: mixers to mix the four waveforms of each oscillator
The 16 mini-jacks bottom center: the oscillator outputs for the 4 oscillators of this panel
Bottom left: mixers
Top left: the 295 filter bank
The description of the 4 Buchla band pass filters and the 16 ultra-stable oscillators does not completely fit the panels I restored, so maybe he also had another Serge-Buchla drone machine.