Belgium: Servo-Sound N.V., Bruxelles
we should (IMHO) not forget this manufacturer from the 60s/70s:
Servo-Sound N.V., Bruxelles 6, 115 Rue de Defacque
(maybe founded and/or succeeded by "Korn & Macway" (K&M))
They developed (i.a.?) active laodspeakers with degenerative feedback of diaphragm moovement, and preamplifiers with "stereo-crossing" technique.
The preamplifiers was available in a version with built-in Thorens turntable.
Cause of some development "tricks" the speakers are worthless without
the preamplifier (and vice versa).
The durability seems to be not high-level, so their uncommon products may be
something rare these days.
May I remind the colleagues from Belgium?
Count of Thanks: 11
Just noticed this thread, member of RMOrg only since a few days. Servo-sound effectively built stereo systems around the principle of "motional feedback" before Philips commercialised the idea. I see there is the "FET Multiplex" model present in the database (it is the tuner model, strictly speaking), it also has pictures of the pre-amplifier and the loudspeaker units with built-in power amplifier. I will add those models (pre-amplifier, speakers) and provide schematics and more photos. Even today, the unit doesn't sound too bad (at least the one channel that is better preserved than the other speaker), but it is difficult to service.
The manufacturer quickly disappeared from the market in the early 1970s, probably because of financial reasons. It was said that Philips had bought the rechnology, which I doubt; their motional feedback (MFB) systems seem to be rather different and have withstood time better.