Pioneer Exclusive M3 (1974 - 1976)

The original Exclusive power amplifier, closely related to the SPEC Series. Not yet class A and still adorned with a few non-audiophile 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 Exclusive M4 would put an end to most of this :) The Exclusive M3 and Exclusive C3 were the only ones of the entire series that were decidedly exported to Europe but it seems sales remained marginal...

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 !

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, "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 entering the loudspeakers, to act as muting circuit during power-on cycle and to protect output transistors by controlling overcurrent. A buiilt-in switchable subsonic filter cuts off anything below 8Hz, with a 6dB/octave slope. 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.

The M3 was meant to be the "soul of audio" and each M3 was delivered with its own technical data-sheet.