Part of the "absolute" preamplifiers then - and still today.
All circuits are biased in push-pull Class A and rely on cascode connections for low NFB amounts and high-frequency linearity.
The phono sections is a three-stage cascode (first stage in p-p differential, the other two in p-p), DC-Servo is applied in all stages, completely dual-mono structure with six constant-voltage power-supplies coming out of each transformer and feeding each of the six modules - that's 36 separate power-supplies !
The bank of caps holds six 16V / 22,000µF ELNA For Audio -per channel- for an astounding total of 264,000µF.
Modules ?
As the trend for sealed modules was raging then (Pioneer C-Z1, Sony TA-E900, Kyocera B-910 etc), the C-280 has six of those : left and right EQ amp, L and R high-level amp, L and R Head-amp.
Those modules were however, wisely, neither sealed, potted or glued, but simply enclosed in aluminium enclosures acting as heatsinks - Class A oblige.
The MM and MC stages used very strictly selected parts : thin-silvered film audio-use high-purity mica capacitors with silver-coated contacts.
The MC (head-amp) stage is placed before the EQ section and uses low-noise input devices and low NFB impedance.
Signal paths are shortened with the use of relays sealed with pressurized nitrogen gas which contact points are either gold-plated or silver-palladium ; all relays have four contact points wired in parallel.
1µm-plating rhodium for all connecting terminals (back-side, including the 600 Ohm XLR balanced), persimmon wood enclosure (top and sides), and hidden secondary controls (front) : L/R level controls for fine-balancing, subsonic filter, three-step MC loading, tape dubbing and three-step loudness compensator.
The attenuator probably comes from ALPS but I have no details on which one it is or how many gangs it has (four or six).
Available in somewhat extended version (C-280L) and later on as ultimate of the ultimate (C-280V) from 1986 to 1990.
Costing a fortune then, the C-280 still costs a a lot today - peak of an era.