Halcro dm58 monoblock power amplifier Page 2

Much of the rest of the dm58's circuitry is said to be based on concepts from microwave and ultra-high-frequency electronics. According to Halcro's US importer, Philip O'Hanlon, were most electrical engineers to examine a schematic of the Halcro, few would even recognize it as being an audio amplifier. Twelve MOSFETs provide the final amplification and are connected to the left side panel, which serves as a chimneying heatsink. The amps run in class-AB biased toward class-A, and fanatical attention has been devoted to ensuring that each section's ultra-low-distortion amplification of the signal is passed on to the next section intact. No global feedback is used in the dm58, though minimal amounts are used in discretely nested loops. Very conservatively rated at 200W into 8 ohms and 350Wpc into 4 ohms, the Halcro is said to be capable of extended bursts of nearly two kilowatts without exceeding its distortion specifications. There is no speaker that will overtax these amplifiers.

The Halcro is extraordinarily efficient in its use of electricity. It draws no more than 350W from the wall, even when producing its full power output of 200W into 8 ohms. O'Hanlon recommended that the amps be left on in idle—not standby—at all times. The heatsinks never got more than slightly warm. Curiously, the amps were only slightly warmer even after lengthy, high-power listening sessions.

That the Halcros are bursting with technological razzmatazz is not surprising. Bruce Candy holds Ph.D.s in physics and applied mathematics, and has taught at universities in England, France, and Australia. He is also the chief research scientist at Australia's Minelab, said to be the world's leading manufacturer of metal-detection equipment and mine-sensing devices. Minelab provides the United Nations and the US military with the mine-locating equipment used in hot spots like Afghanistan. As O'Hanlon pointed out with a laugh, that is not the sort of application in which succeeding "most of the time" is acceptable.

Candy is not a pure technical theorist, however. He is also a lifelong audiophile who, at age 13, began homebrewing his own tube amps. The conceptual genesis of the dm58 was Candy's desire to build an amplifier that combined all the virtues of tube and solid-state designs. After extensive experimentation, the dm58 emerged and Halcro was incorporated to manufacture Candy's audio designs. By the time you read this review, Halcro will have introduced a line stage and a full-function preamp with phono stage. A stereo amplifier, CD player, and multichannel gear should arrive within the next year or so.

Finally got it hooked up, Captain!
The Halcros presented a definite challenge to my sources and cables. Every change resulted in audible differences that were not only clear, but sometimes startling. Much careful listening was required to determine which ancillaries were sufficiently neutral to allow the amps to show their best. For final evaluative listening, I settled on the Rowland Synergy IIi line stage paired with its sibling Cadence phono stage, with the tubed Manley Steelhead phono preamp and Atma-Sphere's MP-3 line stage as alternate references. Interconnects were all Nordost Valhalla, with Nordost's Valhalla speaker cables on the mid/treble and SPM on the woofers of the EgglestonWorks Andra II loudspeakers. Acoustic Zen Gargantua and Custom Power Cord Company Top Gun HCFi power cords both worked superbly in supplying the Halcros with the necessary juice.

Give me warp drive now, Mr. Scott!
I will not soon forget my reaction to the first LPs and CDs I played through the dm58: utter disbelief. The dynamics, purity, and total transparency were beyond anything in my prior experience. Hearing the Halcros at a show was not even close to a proper preview of what they could do in a controlled situation.

After my initial shock and amazement had abated somewhat, I began wondering whether the Halcros were somewhat bright and forward in the upper mids/lower treble. Then the bulb over my head came slowly on: my first listening binge had been exclusively to rock CDs and "Golden Age" orchestral LPs. Most nonclassical recordings are juiced up in this "presence" range during the mixing and mastering process, and many classical records from the 1958-65 era were made with microphones that, for all their virtues, had peaky top-end responses (footnote 3).

As LP followed CD and vice versa, the Halcros proved themselves transcendently neutral. Dry, dull, or aggressive recordings sounded much more so through the dm58s, while plush, overstuffed marshmallows sounded sweeter and cushier than ever, albeit more transparent than I had ever heard before. By definition, the "colorations" I'd thought I'd heard with some recordings were not that at all, as they were mutually exclusive and entirely recording-specific. What I was hearing was the unalloyed sound of the music as recorded. Depending on the recordings and the associated equipment, this was not always a good thing.

Footnote 3: The admittedly wonderful-sounding Neumann M50 omni used by Decca, for example, gently rose on-axis above 3kHz to reach +5dB at 15kHz, while the classic Neumann U47 in cardioid mode had a +3dB shelf on-axis between 3kHz and 15kHz.—John Atkinson
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