Усилители мощности стерео — McIntosh MC275

The MC275 is a two-channel vacuum tube power amplifier from McIntosh, now in its sixth generation. It first appeared in 1961, left production in 1971 and returned in 1993 as a commemorative edition honouring co-founder Gordon Gow. The earlier versions, built between 1961 and 2015, are listed in McIntosh's own legacy archive, and the present model adds tighter bass control and a thermally quieter circuit compared with those.

Key specs that matter

Stereo operation gives 75 W per channel into 4, 8 or 16 ohm, and bridged to mono it gives 150 W into 2, 4 or 8 ohm. Total harmonic distortion is 0.5% maximum across the audio band and 0.25% or lower at 1 kHz. Signal-to-noise is 105 dB below rated output, dynamic headroom 1.2 dB and damping factor above 22. Response is +0, -0.5 dB from 20 Hz to 20 kHz and +0, -3 dB from 10 Hz to 100 kHz. The tube set consists of four KT88 output tubes plus four 12AT7 and three 12AX7A small signal tubes. The amplifier is 41.9 cm wide, 21.6 cm high and 30.5 cm deep, and weighs 30.5 kg.

Engineering and use context

McIntosh builds the output section around its patented Unity Coupled Circuit. Each output transformer carries a pair of bifilar primary windings, serving the plates and the cathodes separately, and the secondary is interleaved with those primaries, giving very close coupling, flat response and wide power bandwidth. McIntosh calls it the widest bandwidth output transformer it makes. A regulated power supply with a large core transformer supports the tubes, and Sentry Monitor provides fuse-less short-circuit protection. Tri-colour LEDs under the small signal tubes show amber during warm-up, green in normal operation and red when an output tube fails. Ceramic tube sockets have gold-plated contacts, the output tube sockets have air-pipe cooling at their bases, and two gold-plated jumper bars are supplied for parallel mono operation. The chassis is polished stainless steel. Signal enters through XLR or RCA sockets, and speakers attach to Solid Cinch posts.

Pairing

The highest-impedance tap in stereo mode allows older high-impedance speakers to be used, while mono mode lets two units drive harder loads. Speakers of moderate to high sensitivity make the best use of its moderate power. The power control jack switches the amplifier and its tube lighting from a McIntosh preamplifier.

Alternatives

The McIntosh MC2152 70th Anniversary, made from 2019 to 2022, is a two-channel tube amplifier with Unity Coupled Circuit transformers rated at 150 W per channel.