The actual Moog Theremins are in fact true heterodyning designs. But if I remember well, there were rumours that the Big Briar 91 series had a totally different circuit design:
[i]This is the inside of the instrument. Unlike the original RCA theremins, Robert Moog's SERIES 91 instruments do not produce their tone using the heterodyne principle although the gestural controls function identically. The signature of the late Dr. Moog, dated June 1997, can be seen on the inside.[/i]
(found on http://www.peterpringle.com/series91a.html)
[i]This is the inside of the instrument. Unlike the original RCA theremins, Robert Moog's SERIES 91 instruments do not produce their tone using the heterodyne principle although the gestural controls function identically. The signature of the late Dr. Moog, dated June 1997, can be seen on the inside.[/i]
(found on http://www.peterpringle.com/series91a.html)
