Pioneer M-91

Pioneer M-90a

1 9 8 8 1988
1 9 9 7 1997

preliminary

Companions to the C-90a and C-91 preamplifiers, the original M-90 and the subsequent M-90a/M-91 were built quite differently, although they do look... identical.
The M-91 is the USA name, under the "Elite" tag and M-90a is the EU/JP name.


The M-90a has the same basic structure as the original M-90 but swaps the EI transformers with the cast-iron trafos and the thin-fin heatsinks with beefier diecasts honeycombs ; caps are maintained at 48,000µF.

Also a thick two-part top plate was added, 1,6mm honeycomb bottom chassis, resin-cast caps, five cell-polymer-filled insulators - and more to mainly strengthen mechanical stability and heat dissipation : going from 20kg to 27,3kg !

The original EI transformers were however seemingly kept for the non-JP and non-US versions ; and the added top plate seemingly was for the units with potted transformers only...
European models weigh 23kg and therefore only saw half of the upgrades between the original M-90 and the M-90a / M-91.

Specs and features are otherwise identical : Non-Switching structure, 70µ PCB tracks, input/output comparators and very large and very flashy red meters.

Three inputs available : CD Direct, Line Direct and Control amp.
The first two bypass the input stages and buffers but go through the front volume pot ; said volume and switches in fact use a long shaft and relays, respectively, to keep signal paths as short as possible.

The small front flap hides speaker pair selectors (A/B), a welcome display on/off switch and a headphones plug.

A two-position switch at the back allows to select speaker's impedance, the 4 Ohm...6 Ohm position being restricted to using only one pair of loudspeakers - the M-91 is a high quality powerhouse but it isn't an MX-10000 !

Although the C-91 was replaced in 1993 by more obviously home-theater oriented receivers, the M-91 was kept available in the USA until 1997, alongwith the M-72 and C-72 combo.

Pioneer M-91, image 1 Pioneer M-91, image 2 Pioneer M-91, image 3
Pioneer M-91 specifications
Title Value
Power output : 2x 200W (8 Ohm, 20Hz...20Khz, 0,003% THD)
THD : 0,003% (rated power, 8 Ohm, 20Hz...20Khz)
IMD : 0,002% (rated power, 8 Ohm)
Frequency response : 20Hz...20Khz (+0dB / -0,1dB)
S/N ratio : 125dB (IHF, input shorted, A-network)
Inputs : 1V / 50kOhm ("control amp")
1V / 50kOhm ("cd direct")
1V / 50kOhm ("line direct")
Outputs : low impedance (headphones)
speakers A / B / A+B / Off
PC : 850W (M-91)
Dimensions : 45,7 x 16,3 x 43,2cm
Weight : 27,3 (M-91)
page online since : july 2008
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