Pre/Power Amplifiers

McIntosh’s original MC275 featured as an ‘Audio Milestone’ [HFN Dec ’10], but what’s reviewed here is the current production version of this most famous power amplifier. It’s the same as the 2011 Anniversary Edition but with stainless steel rather than a gold chassis. Its most spectacular outward feature, described in staid McIntosh tech-speak as ‘small tube illumination for amplifier status operation’, comprises LEDs indicating status or output tube failure. This is a part of a protection circuit system which will also shut the amp down if speaker wires are shorted or there is a gross impedance mismatch.

On seeing Siltech’s pre/power combo you might think it incorporates a separate power supply. In fact, this unusual design splits the power amplifier into separate interstage (voltage gain) and current amplifier sections. The combo’s C1 tube preamplifier (pictured) features a rechargeable battery power supply as does the V1 voltage stage of the two-box power amplifier. Of course, running the complete V1/P1 amplifier from a battery would be wholly impractical, so the P1 is mains powered.

This lavishly-built C600 preamplifier and unusual looking partnering M600 monoblocks [not shown] are TAD Labs’ ‘Reference’ amplifiers. The C600 preamp’s aluminium subchassis is 33mm thick and weighs 15kg alone, designed to resist acoustic vibration and provide a ‘low and stable ground potential’, says the company. Removing the preamp’s top plate reveals its dual mono construction and all-discrete signal path; it’s a fully balanced design. The power supply, with its massive transformer, is a separate ‘hideaway’ unit.

The Virgo preamplifier and Centaur monoblocks reviewed here are models from Constellation’s ‘economy’ Performance range, yet total £72,500. As for Reference prices, we shudder to think… While a pretty enough design, the Virgo is rather anodyne, its greyness John Major-like. A plain-Jane outboard power supply feeds it via two umbilical cables, connecting at the back where you find rows of both XLRs and phono sockets for every input and output – four sources, two sets of outputs and RS232 and USB inputs for networks and firmware upgrades. At the front, the central panel’s 432x230-pixel screen is flanked by rotaries for balance and volume, while other operations are accessed through menus activated by a row of buttons under the display panel.

You want big valves? Really big? NAT has cooked up a monoblock with a mortadella-fat QB 5/1750 tetrode, and a preamp worthy of the honour. Enter Utopia and Transmitter Any reservations I may have had about Eastern European amplifiers were put to rest by the NAT Se1 MkII reviewed in Aug ’10. It was time, I thought, to stop treating the former Communist Bloc as if it were the equivalent of China circa 1993. If anything, countries like Serbia, Bulgaria and others under the grip of the Commies for a half-century had a much better chance at conquering the high-end than the Chinese did, because they had greater hands-on experience.

Anniversary edition of the Reference five splits into two boxes for improved performance Released to commemorate the 40th anniversary of the company’s Reference preamp, the Anniversary Ref 5 promises to address the few solutions not available in its recently unveiled single-chassis version. This two-chassis model sees the valve power supply relegated to a box of its own and, being a true dual-mono layout, two fat umbilical cords connect it to the chassis. Under the lid can be found an all-valve, zero feedback, pure Class A circuit employing four 6H30 triodes per channel, again dual-mono, while mounted on the bottom of the main board are four massive custom Teflon coupling capacitors, weighing around a kilo apiece. Each valve is fitted with a now-familiar damping ring; the main circuitry is fitted to a large mother board; daughter boards deal with the front panel and the socketry.

The latest Levinson product is a consummate music maker New electronics bearing the Mark Levinson badge don’t appear too often. When they do, the world of high-end audio expects them to be exemplary. In producing its first switching amplifier, the ML design team has been able to scale things down to (almost) manageable proportions. The benefits of Class D amplifiers include increased efficiency enabling greater power output while requiring less heat dissipation in smaller, lighter and more affordable packages.