It looks like it could be a Schoeps type +- capsule supply (trim might adjust the capsule voltage) and I would QUESS something like a 87 circuit because of the transformer and capsule
interesting at about 6:50
https://www.youtube.com/watch?v=4PzRCPRTPv0
interesting at about 6:50
https://www.youtube.com/watch?v=4PzRCPRTPv0