The original Exclusive power amplifier, somewhat related to the SPEC-2 export powerhouse.
The M3 and Exclusive C3 were the only ones of the entire series that were decidedly exported to Europe but it seems sales remained marginal...
And if Pioneer only made one Exclusive preamp throughout the 1970s, the M3 was quickly complemented by the Exclusive M4.
Not yet Class A and still adorned with a few "non-audiophile" (in retrospect) features such as three loudspeaker pairs terminals, gain trim pots for said pairs, two pairs of RCA inputs, and 1V or 2V input level switches...
The M4 would put an end to most of this and go full Class A :)
Unlike the later siblings (M5, M5a and M6), the M3 still bears some (limited) amounts of negative feedback, but, like the latter, it already had glass-epoxy boards - terribly expensive, especially in 1973 !
The power supply section consists of a l a r g e cut-core power transformer and two 33,000µF capacitors.
PCB tracks are extra-large, too, and glass epoxy as well : exclusive is Exclusive is eXclusive.
2-stage differential amplifiers are used for temperature fluctuations ; the pre-driver stage is push-pull Class-A operated ; the output stage is a 3-stage Darlington triple push-pull DC and OCL.
The differential 2-stage amp has an "ideal balance of excellent open-loop characteristics and a small amount of NFB to contribute to linearity and objective performance".
The DC balance in the pre-driver stage is adjusted for optimum low distortion and transient response.
The protection circuit is built-in to prevent DC voltage from reaching the loudspeakers, to act as muting circuit during power-on cycle and to protect output transistors by controlling overcurrent.
The M3 was meant to be the "soul of audio" and each Exclusive M3 was delivered with its own technical data-sheet.
The very interesting design prototyping images will be added at a later date, alongwith a few more detailed images.