Launched two years after the Exclusive M3 in Japan as a would-be Exclusive, the 1975 M-77 became for the export markets the famed SPEC-2 powerhouse in 1977.
If the circuits are partly similar, the execution isn't and Pioneer kept a fair distance between the M-77 and the Exclusive M3.
The M-77 cost 180,000¥, the Exclusive M3 315,000¥ so... smaller transformer (but toroidal !), a more standard layout and no luxurious wood enclosure either.
Circuit-wise, the SPEC-1 has an Class A pre-driver stage with current mirror circuit ; a 2-stage Darlington DC - OCL circuit is employed and a triple push-pull circuit for the output stage.
Relays act as protection circuit at the pre-driver and output stages, and also during power on/off, when the current surge reaches... 300 amperes !
The capacitors are 15,000µF each, for a total of 60,000µF ; a back switch allows to select speakers' 4 Ohm or 8 Ohm (nominal) impedance.
Added to the M-77 for its SPEC-2 export version is... nothing : they are the same.
The M-77 sold somewhat poorly in Japan and vanished rapidly, the SPEC-2 sold very well elsewhere, remaining available in Germany as late as 1980 with stocks lasting quite probably even longer than that.
Pioneer was then at the A-9 and the Communication Series but demand was still there for old-fashioned silver with big VU meters.