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MC2 Audio S-series

Class-AB Power Amplifiers
By Hugh Robjohns

MC2 Audio S-series

Offering flawless audio quality, could these prove the perfect partner to your high-end passive monitors?

The modern trend for active loudspeakers in the studio-monitor market has meant that there are a lot of very high-quality passive studio monitors on the second-hand market. Of course, such speakers need high-quality power amplifiers to drive them...

Founded by Terry Clark and Ian McCarthy in 1993 MC2 Audio are a British company who make innovative, high-quality power amps for the live-sound and studio markets. There are currently four MC2 Audio amplifier product lines, and this S-series ‘Signature Range’ is aimed squarely at studios and audiophiles. There are two S-series models, the S-800 and the S-1400. Both are surprisingly compact 2U rackmount designs, but they’re reassuringly heavy beasts — the S-800 weighs 20.5kg and the more powerful S-1400, 23.25kg. The front panel not being sufficiently robust to support amps of this weight in a rack unaided, additional rear-mounting support plates are included. All MC Audio products are covered by a five-year warranty.

Although some of MC2 Audio’s designs are class-D, the designers chose to equip the S-series with Class-AB output stages combined with a unique current-driven floating drive stage. Simple analogue input attenuators are provided, and sophisticated (hidden-until-needed) ‘side-chain’ limiters are on hand, to prevent clipping distortion and speaker damage. Full DC, thermal and short-circuit protection are also included, and the substantial power supply is built around a bespoke and shielded toroidal transformer.

Cramming so much potential power into a 2U rackmount case requires forced air cooling and these amps employ ‘intelligently controlled’ low-noise fans, which suck air in from the front via foam filters and exhaust it at the rear. There are no conventional exterior heat-sink fins.

The audio input connections take the form of female chassis-mounted XLRs, with parallel-wired male XLR loop-thrus for daisy-chaining to other amps. The speakers are connected using two- or four-pole Speakons, with the amplifier output wired to Pins 1+ and 1-. Usefully, the channel-A Speakon carries Channel B’s output on pins 2+ and 2- for convenient single-plug bi-amping or bridged operations. The very substantial mains cable is permanently attached and terminated in bare (tinned) wires; persuading them to fit into a standard 13A mains plug is a major challenge, but as the S-1400 can draw nearly 17A and the S-800 nearly 15A when running flat out, these amps should really be wired directly into a ‘cooker outlet’ or blue IEC 60309 (CEE-form) 16A connector.

The front-panel controls comprise an on/off rocker switch and separate rotary input attenuation knobs for each channel. Seven status LEDs are also provided, starting with signal-present (green) and limiter-active (orange) indicators for each channel. In the centre of the panel, a green LED lights after the amplifier completes a system check on power-up, and there are two LEDs below, one labelled A/P (audio protect) illuminates red if any of the protection circuits are activated, and the second lights green when the bridged-output mode is selected (with a push button on the rear panel).

MC2 Audio’s published technical specifications are impressively comprehensive, even quoting the typical current draw and heat dissipations at different situations. Both amps have similar THD figures, measuring below 0.008 percent (on a par with the very best amplifiers), and the frequency response is within 0.5dB between 20Hz and 20kHz. Both models can also be switched between 32 and 36 dB of gain, and at the lower gain settings full output is achieved with input levels of +8dBu for the S-1400 and +5.5dBu for the S-800. (When switched for 36dB gain, the maximum output is achieved with 4dB lower input levels in both cases). Measured using continuous music with a crest-factor of 4.8 (14dB), the S-800 provides 475W of output power per channel into 8Ω, while the beefier S-1400 manages 775W into 8Ω. The corresponding figures for 4Ω and 2Ω loads are 950W and 1500W, and 1550W and 1800W respectively. Both amps can also be used in a bridged-mono mode to deliver 3.1kW or 3.6kW, respectively, into 4Ω!

I listened to the S-1400, hooking it up to PMC IB1 monitors in place of my trusty Bryston 4B. The S-1400 has slightly higher gain than the Bryston, so a small adjustment to the input attenuators was required to match levels. PMC monitors love power — the more the better — and that was evident with the S-1400, which controlled the IB1s superbly. I couldn’t fault the MC2 Audio amp’s transparency or detail resolution at all, and it was frighteningly powerful when called upon while retaining absolute control at all times. It’s pretty rare that I ever call upon the Bryston’s conservative 250W of power, so 775W in the S-1400 was rather overkill and hugely underused in my case!

The only downside for me, not surprisingly, was the cooling fans, which run at varying speeds, depending on the amount of work the amp is doing and the resulting internal temperature, but the exhaust air is pretty warm, so they are clearly doing a necessary job very well. Initially, the fans didn’t run at all, but even at low listening levels they soon started up and generated a similar level of noise to a typical (previous generation) Mac Pro. With the amp on the floor between my monitors, the fan noise was an issue for me — it may be less of a problem if the amp is mounted in an acoustically damped rack or separate machine room.

Ignoring the fan-cooling aspect, MC2 Audio’s S-series amplifiers are impressively powerful beasts, combining genuine professional ruggedness with audiophile levels of resolution and performance. They come in an unusually compact form factor given the extraordinary output power. For most typical project-studio applications I suspect the S-800 would be more than sufficient, but in big rooms with big speakers, the S-1400 makes even the massive Bryston 14BSST look a bit puny! Hugh Robjohns

Alternatives

There are very few studio- or audiophile-grade power amplifiers that offer anything like the rated power of MC2 Audio’s S-Series products in such a small chassis size. The obvious fan-less contenders are Bryston’s SST range and some of the more exotic hi-fi products from the likes of Krell. There are plenty of fan-cooled Class D live-sound amps that can deliver similar amounts of power, although few are as transparent-sounding as the S-series.

Pros

  • Very ruggedly engineered.
  • Massively powerful for a 2U rackmount design.
  • Extremely transparent and high-resolution.
  • Class-AB, not class-D.
  • Comprehensive but non-intrusive protection circuitry.

Cons

  • Cooling fans.

Summary

These are superbly engineered and very high-powered professional class-AB power amplifiers, and they occupy only 2U of rack space. The forced-air cooling fans, though, may render these amps unsuitable for some applications.

information

S-1400 £3000, S-800 £2460. Prices include VAT.

www.polaraudio.co.uk

www.mc2-audio.co.uk

S-1400 $4400, S-800 $3600.

www.g1limited.com

www.mc2-audio.co.uk

Published April 2015