June 1, 2002
Halcro dm58 Mono Amplifiers
On the face of it, the claim has always seemed preposterous: "Distortion of less than 1000 parts per billion"!! (For those who need a refresher in matters of punctuation, the double exclamation points come from me, not from the Halcro dm58 monoblock amplifiers manufacturer.) Heres another claim that has caused a non-Halcro importer I know to sniff in disbelief: "99.9999% pure reproduction at full power." As one tube wag observed, "Thats like saying six-nines pure reproduction." Yet a non-audiophile friend, who absolutely lacks the audiofillets esoteric dialectic or the credentials to offer anything worthwhile to the tribe -- at least to many of us snobbier members -- uttered this upon hearing the dm58s when they were initially installed to drive my resident MartinLogan Prodigy electrostatics: "Good God, effortless, it sounds so f$%**^ effortless. And intimate. Its like she [Jacintha] is singing just for me!"
Amen, brother, the near-perfect audiophile description, speaking ultimately to dynamics and musicality. And over the next three months these two notions would manifest themselves in my notes -- along with "ungodly transparent," "frighteningly powerful," "stunning articulation," "simultaneously explosive and subtle," "tuneful," and a slew of others that make me sound more like the courts sycophant than one of its skeptics.
How they sing
The conventions of audiofillet journalism insist on a sequence of presentation when reviewing a piece of gear. Generally, the package is fronted by descriptions of physical architecture, audio and power boards, quality of parts, number of RCA/XLR jacks, and other such minutiae, and though theres no criticism intended of this approach to critiquing, it actually seems more proper to begin this exegesis about the Wonder from Down Under with the music. The tech stuff, whatever is available, considering the impossibility of access to the Halcros proprietary innards, will come a bit later for those you who must have it.
When reproduced music becomes a vehicle of transport to that ineffable place, closer to the moment of creation, whether in the studio or at a live venue, my response becomes kinesthetic. The body relaxes in that special way when live music is played; the upper torso can fall back into the cushion; the shoulders stop shrugging; the respiration and heart beat(s) begin to match the pace (and passion) of the proceedings. Much of that kinesthesia for me is rooted in, among other things, a sense of overtone and harmonic structure, in the rightness of tonality or timbre, in the lack of peakiness at the wrong moment. Simply put, my body responds to the perceived fleshiness of notes, bars, lines, melodies and so on that unfold between the speakers. And in so many ways, the Halcros deliver this sense -- time and again.
Despite a re-production date of 1989, as a compact disc release, Ella Fitzgeralds Clap Hands, Here Comes Charlie! [Verve 835 646-2] is simply a masterpiece, a surprisingly engaging sonic marvel in most systems, yet eerily real-sounding in a higher-res setup. Take the bass line and triangle in the opening of "My Reverie." Joe Mondragons bass is meaty, fleshy, woody without sounding overripe. The notes are a seamless extension of the marriage of plucked wire and wooden chamber. Sonorous comes to mind. Over the bass, the struck triangle rides with a natural edge, each leading transient sounding appropriately metallic with the initial strike and then decaying naturally into near inaudibility before you hear the next strike. That decay is liquid in its slide into silence.
Then theres Ellas young voice -- the original tapes to this session go back to 1961 -- with phrasing that wraps itself around the soul. Part of the Halcro magic here has to do with Ellas ability to generate a vocal glissando with certain words, yet so many amps will turn this rise or inflection into a peaky brittleness. And this can be particularly noticeable with the Prodigys, which require more power reserve to handle the drop in impedance as the frequency climbs. With the Halcro dm58s, all was smooth and natural, no wincing from start to finish. No peakiness. Effortlessness. Just relaxation.
As an aside regarding issues of subtlety, whatever tape hiss exists on Clap Hands, as well as other compact discs remastered from tapes, the hiss does not distract: Generally, hiss and music become Siamese twins in the same crib when lesser amps are in service. However, in tandem with the Marantz Master Reference SA-1 SACD/CD player upstream, which first oh so artfully separates the two soundfields -- music and hiss -- the Halcros easily maintain that sense of separateness, a natural boundary if you will, between the two, allowing each to exist on its own. The hiss simply does not impede on the sense of overtone structure inherently present on the disc. Magic, indeed. Musical, indeed. Something to behold -- or, to coin a word, should we use behear?
Whatever uniqueness is unearthed by the front-end, one can be sure that the Halcros will let it come through unscathed (of course the preamp and wire must be up to the task, and for this test the stunningly neutral Meitner Switchman II preamp and Valhalla cabling by Nordost proved to be an ideal match). Heres a bit of that uniqueness Im talking about: The backing vocal on "I Wont Back Down" on Johnny Cashs American III: Solitary Man [American 69691], while normally unidentifiable, is clearly the voice of Tom Petty, the songs author. Nice touch this, unavailable to my perception until the Halcros sat in residence. And while Im speaking of voices, the Halcros are nothing short of spectacular in revealing not merely the melodic lines but, somehow, the sense inhabiting these lines. Theres that playfulness to the anger evidenced by Holly Cole in "Evrything Ive Got" on Dont Smoke in Bed [Capitol CDP ottt 7 81198 2 1]: Through the Halcros, Cole's reading of the line "Theres a trick with a knife Im learning to do " suddenly becomes loaded with meaning. Or take that subtle nasalness, her French conceit, inhabiting "Je Ne TAime." One need not understand the language to comprehend the feelings conveyed in the tune.
What much of this seems to come down to is the Halcros ability to reveal subtlety in textural structure of harmonic overtones, an overlayering that must come through if music is to become a living, breathing entity. The impossibly low noise floor of the dm58s allows for this to happen, over and over again. The Halcros sense of truth to the music is frighteningly disconcerting -- you want piloerection, youve got it, buddy.
Speed, dynamic ability, we have these in spades too, considering the response of the Prodigys. A wonderful disc for discovering these qualities is a little-known gem: En*Trance by Conrad Praetzel [Paelo Music PL4003-23]. Largely keyboards and sampled percussion, this compact disc can shake the marrow, from its fast transients to his depthful electronic bass and its multilayering. "Stone Soup," in particular, melds into a series of dynamic intricacies -- not only Praetzels eletronica but includes electric sitar and dobro by Robert Powell, flamenco guitar by Solomon Feldthouse, and sampled drum kit by Bryan Laser. With lesser gear, this CD, the discovery of which I owe to Harry Pearson, is flat, lifeless, droning more suitable for trance states at a rave and not soul-stirring in the listening room. Through the Halcros, nuance, speed, depth and seemingly infinite transparency turn En*Trance into a kinesthetic experience that fills the soul with new possibilities.
And if you prefer large, room-crushing atmospherics that bring on ecstasies, try running Pomp and Pipes [Reference Recordings RR58] and Trittico [Reference Recordings RR52CD] through the Halcros. Until the amps were in situ, these recordings lacked that the ultimate in visceral involvement, sounding somewhat flattened. Not so with the Halcros, which delivered as much power as these recordings demand, and there seemed power to spare: no compression or hardening was noted during swells in the music. But beyond the power, it was the musical shadings, even amidst all the powerful pomp, that shone through clearly, involvingly.
Obviously, the Halcros are the cats pajamas -- they do music and do it exceedingly well.
Gleaning the guts
Designer Bruce Candys labor of love represents nothing less that the successful marriage of form and function -- a fully realized product. Externally, the dm58 vaults skyward, consisting to two boxlike modules attached between a pair of winglike pillars, each of which rests on a solid mahogany foot. Top to bottom, the finish is satiny anodized aluminum. The footprint is a healthy 16"W by 16"D by 31"H.
A trick air-pressure switch under the upper module turns on the amplifier from standby to active mode. A full power-on switch is located at the bottom of the lower module. Adjacent to this youll find your IEC inlet as well. The rear of the upper module, which houses the audio section of the dm58, reveals RCA and XLR inputs, with a rotary switch for activating either balanced or unbalanced mode.
The back of the top module also sports output jacks, which are covered with rubber grips for ease of tightening, an ingenious construct that allows you to tighten down the nuts readily by hand. I was able to truly tighten down the spade-backed Valhalla cables for a solid connection.
The left pillar of each monoblock acts as a heatsink for the output MOSFETs, though throughout their residence in my home, the Halcro dm58s never felt other than slightly warm to the touch. That they drove the somewhat difficult MartinLogan Prodigys, often to prodigious volumes that overloaded the room, speaks eloquently to Candys implementation of unique design topologies. In laymens terms, the amps never broke a sweat, no matter how trying the demands, even during the most demanding passages of Vaughn Williamss Symphony No.7, the infamous "Sinfonia Antartica" with its howling, yet often delicate, high frequencies, and controlled yet powerful bass that emanated from the earths very subterranean depths.
The upper module houses, simply put, the audio circuitry, while the lower is dedicated to the power side of the equation, an arrangement that no doubt prevents interference from magnetic and electromagnetic induction, vibration, and the lot.
In addition to master-engineer status with advanced degrees in applied mathematics and physics, Bruce Candy is equally adept at marketing by generating mystique around his designs. One simply cannot gain access to the dm58s -- thats how well their secrets are contained -- and Candy, at best, will drop mere hints ("tantalizing scraps of information," as TAS's Dan Sweeney put it) in one interview after another about the guts of his ground-breaking designs. Hence, the following is a compilation of random bits and pieces -- not in any relevant order -- gleaned from assorted writers. These should not be viewed as the last word on matters technical.(What we can say with a modicum of certainty can be attributed to various notable and savvy sources, including Sweeney, Ken Kessler in Hi-Fi News, and Isao Shibazaki in MJ magazine).
Candys design relies on engineering convention -- differential input, main gain-stage loading with a current mirror, unity-gain power-output stage, etc. -- but the circuits of each stage are not especially conventional, and at present that is all we know for sure about their construction. According to Sweeney, certain parts are said to have been originally designed for non-audio components. In this respect, one can assume that Candys topology includes an adaptation of sensitive circuitry used in metal detectors, his real money-making enterprise, which, under the name of Minelab, allows Candy to hold sway over 80% of the worlds mine- and gold-detection equipment business. Certainly implementation of such sensitive materials can go a long way toward eliminating or controlling distortion byproducts. Shibazaki adds a bit more to the puzzle, noting that Candy utilizes quite unique parts in the dm58 and the larger, costlier dm68 (such as 18GHz-bandwidth transistors found in microwave circuits), all of which allows the final output to be clean and nearly distortionless.
After an interview Candy had with Shibazaki, the Japanese journalist noted that the Halcro's lower module is composed of three-layers containing an AC line filter in one section, an AC/DC-converter board in the second layer, and a DC/DC-converter board on the third layer. As well, the unit relies on a large switch-mode power supply (handling 85V-270V without a selector switch), which ultimately allows for more than 1000 watts at 1 ohm (220 at 8), potentially explaining the effortless quality my friend sensed through the Prodigys, said drop to 1 ohm when frequencies approach 20kHz.
Additionally, the power module contains one element that clearly adds significantly to a nearly non-existent noise floor. The module, and by extension the amplifier, is one of the few audio products thus far available in North America that contains power-factor-correction circuits. This implementation allows his amps, according to a white paper by Bruce Candy, to deliver maximum power output -- a near ideal power factor of 1 -- regardless of the demands placed on it, compared to the much higher numbers (and thus greater distortion potential) generated by amps relying on more traditional peak-rectified topologies facing identical demands.
Again, the implementation of audio circuits is "pure textbook," according to Sweeney. However, the "infinite gain and infinite feedback approach used in most low-THD commercial op-amps is not the design principle [Candy] followed in the Halcro units," he adds. And heres some of what Shibazaki noted: In part the amp relies on a "current mirror and asymmetrical single-stage amplification structure." Continues Shibazaki, a "multiple stage will create a complicated distortion [with] high-order harmonics while single-stage creates simple and easy-to-correct distortion." Further, according to Halcro specs, quality parts includes "at least industrial grade" semi-conductors, and electrolytics boasting an operating range of 105 degrees Centigrade.
To further lower distortion potential, the power-amp section contains six-layer PCB boards in an effort to minimize stray magnetic fields. Add extensive use of Farady shields and youve quickly approached what others would call escalating redundancy.
Theres a helluva of lot more assorted information to be gleaned from these and numerous other sources, and if thats what you need to know, start hunting cause Im running out of space. But no matter what youll glean, the fact remains (for now) that few on earth know the full scope of design characteristics and parts of the dm58s (or the dm68s for that matter), and ultimately, even fewer can measure the beautiful beasts. Only the University of Adelaide in Australia has come close in this respect, but the equipment had to be custom created on a specially constructed bridge circuit to be able to do that (in fairness, the testing was paid for by TASs Sweeney, and we owe him a debt of gratitude for that).
Bottom line is, the amps a winner, a precedent-setting design that has the reviewing community ordering extra boxes of Depends and selling off loved ones to be able to pop for the $25k asking price for the pair. And thats as it should be for something that delivers equal amounts of sublime finesse and brute power in a pair of stunning-looking boxes. But now, with all due respect to my reviewing comrades, a word or two of caution, even for a product that truly needs no cautionary notes.
Ones choice of preamplification is crucial. While finding compatible upstream components is possible, be prepared to look. Its my understanding that the Aloia preamp worked well with these amplifiers, as well as the GRAAF 13.5B preamp, the Musical Fidelity Nu-Vista, the Krell KPS-25sc, and some of the newer Levinson solid-state stuff. For whatever reason, I could not squeeze enough information through my Herron VTSP-1 and Conrad-Johnson 17LS line stages, which have never had problems feeding other solid staters. When Halcros US importer Philip OHanlon, however, allowed the use of a Meitner Switchman II preamp -- which handles virtually any type of input jack, is designed for the professional community, and which subjectively appears not to change one iota what is fed into it -- the Halcros true ability came through. So match carefully.
Additionally, my dyed-in-wool bottlehead buddies, while admitting the dm58s did what few other amps could, noted that their bias toward valves had not been diminished by the Halcros. Their chief concern had to do with holographic dimensionality, that palpable, 3D presence which seems more apparent with tubes, but they would not admit when I prodded them that this very holography is in fact a tube artifact, a distortion, however pleasing it might be. That same sense of holography does not exist when I listen to live music, as was the case the other night in a concert of the Ray Brown Trio. One could certainly tell where individual instruments were located, especially when they generated higher-frequency information, but they were not holographic in the tube sense. And thats what I hear with the Halcro dm58 -- a sense of music pretty damned close to what I heard the other night.
Now, admittedly, Im a tube head myself, but thanks to the Halcros Im no longer so one-sided in my view of amplification. These amps were marvelous, musical, nearly artifact-free. They taught me that one can (at least I can) live with both tube and solid state equally, relishing what each does on its own terms. And thats the highest form of praise I can heap on them.
Halcro dm58 Mono Amplifiers
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