Alongwith the Rotel RC-5000, the C-1 probably remains as the busiest front plate of all time and the antithesis of the "straight wire with gain".
But it seems the C-1 wasn't the antithesis of neutral & natural sound -Yamaha oblige- as, like the B-1 V-FET masterpiece, the C-1 is one of the few preamplifiers that became an instant landmark in audio design.
All-FET, with small-signal V-Fets in some of its stages, constant-current / constant-load / current-mirror / fully-stabilized ±100V / ±33V EQ section, metal film, styrol and mylar caps, separate amp for headphones and a 4-gang volume control.
Variable loudness, acoustic & presence tone shaping plus regular bass/treble with 2-position center/turnover frequencies for all, 4-frequency tone generator plus pink noise position, front pre-out and tape i/o, MIC inputs, 6-position phono impedance trims for inputs 1 & 2 (separately !), pre-out or rec-out meters switch with attenuator - and then some.
Three phono inputs, three tape loops, three line inputs, input level trim pots for all, three pre-outputs, one input to use the meters with an external source, one oscillator output with level pot,
400,000¥ brought a lot in 1975.
Very briefly c. 1978 available in select markets in silver ; available in Japan as late as 1983.
Would be very good-looking if silver and in a custom wood enclosure !