Halcro dm58 Monoblock Amp Reviewed

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There are two piles of magazines, some 57in tall, sitting in my lounge. They consist mainly of hi-fi magazines I can't read until they're 'out of date'. Why? Because I don't want to be influenced by the reviews, and I don't always know whether or not I'll be reviewing a component which I've just seen slammed or praised. Thus it was that I tried to avoid whispers about the Halcro amplifiers from Australia. Even so, I kept hearing about these '******* amazing amps' from all and sundry.

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Not that you need anyone else to tell you that the Halcros are - at the very least - 'different', that they stand-out from the pack. The finish is so good that it's hard to believe we're talking Land of Foster's rather than Land of Liebfraumilch, while the styling reeks of Denmark. Although vertical amplifiers are now very much 'in' (credit goes to - I believe - Mark Levinson) but the Halcros aren't merely vertical: they're modular, and this tower-like construction isn't simply an aesthetic conceit. With a background heavily research-based, Halcro's designer Bruce Candy determined that there were genuine sonic gains to be made by a change to the traditional physical topology, what he calls 'a complete reinterpretation of the amplifier aesthetic.'

Uncommonly pretty, the Halcro consists of an aluminium case with a satin anodised finish. The side panels are finned, while all other surfaces are smooth. To add a touch of the organic, each side panel's lower extremity is a solid mahogany foot, also in a satin finish. On the underside of the bottom module is the AC mains input and the primary on/off switch, which you won't ever want to access again: warm-up time from cold is a day. Instead, there's another switch - a funky 'air pressure' push button - resting underneath the upper module. Press it, and the LED on the lower section changes from red to blue. Behind the upper module are solid spade-connector-only binding posts for bi-wiring, an earthing terminal and inputs for single-ended (phono) or balanced (XLR; a rotary control chooses between the two.

Those modules sandwiched between the two upright sections are the 'housing compartments' containing the Audio Drive Module, the Audio Power Module and the Power Supply Module. Halcro feels that the Audio Drive Module and Audio Power Module 'must be within very close proximity of one another', but are shielded by a massive 5/8in thick plate of non-ferrous metal to prevent any residual non-linear fields from the power stage from feeding back to the input stage. The Power Supply Module, on the other hand, is physically separated from the other components for optimum shielding; the base of the Audio Power Module and the top of the Power Supply Module each have 1/8in thick non-ferrous metal plates. The Audio Power Module also requires 'a major heat sink' to dissipate excess heat, the dual heat sinks housed within the vertical slabs.

But Halcro isn't tunnel-visioned, so the company also recognises that there are other benefits, including the way that separated, screened boxes perfectly suit vertical stacking to create a small footprint. Well, 'Aussie small' at least, because however much the company wants to boast that each 125lb unit occupies less floor space than most conventional amplifiers, a 16x16in footprint is hardly Cinderella-esque. Height, by the way, is an awe-inspiring 31in, so a pair of Halcro dm58s monoblocks is a sight to behold. Cleverly, the company points out that this 'aesthetically relates well to the typical vertical speaker formats', and I have to admit that they looked right at home next to the Wilson WATT Puppy System 6 they were driving. Also mentioned on the unit's behalf were the fact that freestanding amps don't require support stands or additional furniture, and that the sheer acreage provides maximum surface area for heat dissipation. No matter how hard these were driven, they never got more than lukewarm.

Candy describes the amplifier in the comprehensive technical paper as conventional in that its basic circuit consist of a differential input voltage-to-current converter, current mirror, voltage amplifying stage and a unity voltage gain power output stage. It's non-symmetrical because Candy argues that there's 'no such thing' as fully symmetrical - and besides, single-ended triodes are the flavour of the decade, and they ain't symmetrical either. But Candy also has a novel approach to retro: with the dm series amps, he's revived the specifications war.

Candy feels that the nastiest distortions are in the upper frequencies, and he also believes in clean and fast power supplies. But while he's perfectly happy to state that there's no such thing as total symmetry and he's not bothered about producing a skin-singeing true Class A design - the quiescent current is deliberately adjusted to a higher level to minimise crossover distortion - he's also playing the specs game with distortion measured in parts per billion.

The Halcro uses power FETs in the output stage, delivering 200W per chassis into 8 ohms with distortion of less than 4000 parts per billion. This translates into 'fidelity of each pure tone at full power up to 20kHz reproduced at better than 99.9996% purity across the entire audio range.' It features a universal, 'power factor-corrected' power supply with a power factor of one, which automatically operates from 85V through to 270V r.m.s. without any internal or external switches, and boasts series and common mode filtering on the mains input. Like the top Linn amps, the Halcro uses a switch mode power supply, in anticipation of CE regs and adhering to Candy's belief that the grunge produced by conventional power supplies is one of audio's biggest culprits; like the Linn, the dm58, and the higher-powered dm68, lay to rest any worries that the post-CE-approval future would be one free of hugely powerful amplifiers.

Continue reading about the db58 on Page 2.

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