Onkyo A-65

Very very rare integrated amp which seems very very big... through an easy design trick : very big buttons placed within a smaller footprint sized at 41cm in width :)
There's actually no more functions laid out in front than on any other contemporary pre/main - the real works are here inside :

Contemporary of the successful P-306 and M-306 combo, the A-65 is centered around Double Super Servo.
DSS is made of two NFB loops between input and output added to the overall NFB loop : one works on subsonic signals, the other on ground potential to do away with grounding differences between the output of the preamp section and the input of the power amp section.
According to Onkyo, the back current from the loudspeakers is thus eliminated (no less) and results in a skyrocketing x50 current delivery (no less !).

A sort of linear switching circuit is added to minimize distortion produced by output transistors when the latter turn on and off. Electronic relays cut signal and power when DC leak or over-heating lurk around ; the power trafo is itself protected by a dedicated thermo-sensible fuse.
The A-65 sports 4x 12,000µF capacitors and is able to feed three pairs of loudspeakers - but only two at once.
Two phono inputs with three position setting (MM, high MC and MC) should satisfy both Denon DL-103 and Shure V15 MM and MC cartridge users.
A low-impedance preamp output is added for those who want more beef with their corn ; no amplifier input however is provided for those who prefer corn to beef.

I believe the A-65 to have been export only (but can be wrong on this) - the discreetely backlit power, input and muting selectors were inherited from the final PX-100M design just the same.