July 2001

Audio Harmony TWO Harmonic-Enhancement Device

by Aaron Weiss

Review Summary Sound "Expends its effort plumbing for detail and dynamics" -- "performers and performances are injected with a modest shot of adrenaline"; "where bass notes were previously the slightest bit unsure, the TWO carried them with authority." Features "Produces primarily second-order harmonic distortion, with a minimum of odd-order distortion…a harmonic-distortion pattern more similar to tube components than that of solid state." Use Recommended for use between preamp and amp, and requires an extra set of interconnects; adds 5dB of gain, so don't mistake this for the only sonic goody the TWO has to offer. Value "I wouldn’t be surprised if the Audio Harmony TWO lent its charm to a commendable preamplifier more thriftily than would an incremental climb up the preamp ladder."

Test of faith

The world of the audiophile is not unlike a religion -- indeed, for many of us it is precisely that, complete with prayer and tithing. Our religion features a canon of prominent elements whose roles and importance we accept as fundamental: the amplifier, preamplifier and loudspeaker, for instance. And we mustn’t forget the source. Some believe in analog, others in digital, and so we also accept some theological fragmentation, congregations massing in one church or another. Do you seek the absolute sound or a sound that’s absolutely you?

And then there’s our test of faith. Catholics have their weeping billboards and ghostly coffee stains to be sure, and just the same, we have the little black box. Better sound through mysterious gizmos! The little black box, although it might just as well appear in the form of oak, maple, or brushed steel depending on the era, promises a reason for hope. Although unfamiliar, and perhaps even unexplainable, the little black box gives us something to believe in.

Hovering before us today is a particular little black box by the name of Audio Harmony TWO. Especially little, in fact, the $550 USD TWO is more of a little black brick at 6"W x 9"D x 2"H and weighing in at just over four pounds. Like any cauldron of black magic, the TWO couldn’t seem simpler on the outside: the front of the unit contains only a rocker power switch and corresponding red LED beacon. At the rear are two sets of Custom House premium gold-plated RCA jacks, one set for input and one for output, signaling that you will need an extra pair of interconnects for, uh, interconnection. A rear IEC receptacle supports your preferred (or the included) little black power cord.

Technically, the Audio Harmony TWO supports frequency response to 100kHz +/- .2dB; its power bandwidth extends to greater than 1MHz. Its total harmonic distortion is quoted as .025%, signal-to-noise ratio as greater than 100dB, and voltage gain at 5.1dB.

Any discussion of the Audio Harmony TWO requires a very brief course in the matter of distortion. All signal amplification creates distortion. Harmonic distortion occurs at multiples of the original signal. For example, a 100Hz tone could have distortion at 200Hz, 300Hz, 400Hz, 500Hz and so on. The human ear has a difficult time hearing this distortion when it occurs at even multiples of the signal, especially a multiple of two, also known as a second-order harmonic. It’s also said that when we do hear even-order harmonic distortion, we tend to like it. This even-order, second-order-dominant distortion pattern is the signature of vacuum-tube-based audio components. Solid-state components, on the other hand, while more ubiquitous, are generally designed with vanishingly low distortion of all types, although their dominant signature is that of odd-order distortion, where stray frequencies occur at odd integer multiples of the original signal. In general, people don’t find these pleasant.

The Audio Harmony TWO, according to its designer, Bob Jendrejack, "is a class A analog gain stage that operates like a harmonic filter," the result of which is to "remove" higher-order harmonic distortion from the audio signal. More specifically, the Audio Harmony TWO produces primarily second-order total harmonic distortion, with a minimum of odd-order distortion. This, on paper, suggests that the Audio Harmony TWO produces a harmonic-distortion pattern more similar to tube components than that of solid state, although the TWO itself is a solid-state device. Go figure.

Bob Jendrejack launched Audio Harmony in 1998, as business shifts found his harmonic-filtering designs facing the two-channel Harmonic Recovery System produced by Source Components Electronic. Jendrejack chose to introduce a six-channel version of his harmonic-filtering circuit (the Audio Harmony SIX, $895), and following strong press, the two-channel Harmony TWO. Beyond merely a two-channel version of the SIX, the TWO features several design improvements, including increased class-A bias current and a discrete voltage regulator design, while both the TWO and SIX sport Kimber Kable wiring and Wima polypropylene capacitors.

Jendrejack has been engineering in audio for 15 years, including time spent modifying B&K gear through his relationship with Sound Unlimited in Bristol, Connecticut. He plans to follow the TWO with a Signature version, with volume control, headphone jack, and further circuit improvements.

With ears wide open

To help distinguish spirit from phantom in this little black box, I paraded the TWO to the temple: ProAc Response 2S loudspeakers fed by a Primare A20 integrated amplifier, a Marantz CC-65SE CD player as digital source. All components were tethered with DH Labs BL-1 interconnects and biwired Canare 4S8 slung out to the altars -- or rather, loudspeakers.

Audio Harmony recommends that the TWO ideally be placed between the preamp and amplifier to best preserve the filtered signal. Placing the TWO further upstream between the digital source and preamplifier confers the same benefits to the signal, but risks later corruption when the signal then slithers into the preamplifier. In my case, the TWO was perched between source and integrated amplifier. Audio Harmony recommends that the TWO be powered on continuously for maximum performance, and at a thrifty five watts of consumption, this isn’t an unreasonable demand (Californians notwithstanding).

God is in the details?

Even the least subtle among us won’t fail to notice the TWO’s first, but perhaps misleading, impression: the music is louder with the TWO in place. With a 5dB gain in the signal, the TWO bumps out a volume increase that, like the sales tricks in seamier audio salons, may at first mask more profound properties. This isn’t to suggest that the TWO’s gain is a trick by any means. Jendrejack notes that with any less gain, the TWO's circuit would not best convey the desired dynamic range.

Listening beyond the volume shift, the TWO seems to stand on its hind legs, perky and upright in presentation. Some might describe the TWO as forward, but this may be too absolute -- just how far forward is partly a negotiation with a recording’s engineer. Take, for example, Joan Osborne's Relish [Mercury 314526699-2]. On low-end systems, this disc can sound almost unbearably harsh and edgy. On a Creek 4330 integrated amplifier, Osborne spits up the gravel in exchange for sweetness and smoothness. With the Primare A20 on the Creek’s former shelf, she regained some edge, sounded drier -- but more realistically so -- although she was perhaps a bit lean as well. The TWO recovered the disc’s depth, expanding the distance from Osborne's breathiest lows to her tranquil highs. But when she veers harsh, as in the longing that opens "Help Me" -- "You gotta help me baby, I can't do it all by myself" -- her plea becomes a whine, and the TWO doesn’t hide that fact.

Nor does the TWO hide much at all, propping up details that were in some cases flaccid or invisible. The opening four seconds of Osborne’s "St. Teresa," previously assumed to be a silent lead-in, actually contains a low-octave organ sustain, just before the clanging kicks in -- revelation courtesy of the Audio Harmony TWO. Quite a similar discovery can be found near the 4:14 mark of Theodore Dubois’ "Les Sept Paroles du Christ" on Stereophile Test CD [STPH 002-2]. Shortly after a false climax, a period of apparent silence is followed by the true climax of the movement. The TWO didn’t see silence; it saw the solo tenor. He must’ve been there all along, the poor fellow.

The TWO enhanced contrast between background and foreground beyond the useful limits of the listening room -- a room, like any pragmatic compromise, not immune to the Doppler effect of passing traffic, humming appliances, and inconsiderate spring robins’ calls. Scott Walker’s compellingly disturbing Tilt [Mercury DC134CD] is, among other masochistic pleasures, a festival of low-level detail. Although the work itself would remain troubling played even from a clock radio, the TWO’s love of detail magnified a veritable ant colony of low-level activity, exemplified by the scratches, "cracks" and "ticks" scurrying around "Bolivia ’95."

While Scott Walker uses minutia to create a nightmarish but synthetic landscape, detail also lends credibility to an acoustic source. Adele V. Anthony’s solo violin on Mark Levinson Live Recordings at Red Rose Music Volume One [Red Rose Music RRM 01] "Recitativo in Scherzo" is a jaw full of saw teeth. When reproduced too harshly, the trembling waveform of the violin can be diminished to the fidelity of an 8-bit computer sample; too smoothly and you wind up with a Celine Dion hit single. Crests of jagged detail are caught by the TWO as Anthony’s bow scrapes against the strings. The resulting vision, an apparitional solo performance in your own listening room, there with the carpet stain and cereal bowl on the floor, is impossible to refute.

Foundations & fundamentals

At the start of "Twenty-Third Psalm," also from Red Rose Music Volume One, three temple bells ring out with startling accuracy, so richly reverberant that Ella DiBella, resident audio cat, growled, leapt from the futon, and fled the room. Before the Audio Harmony TWO’s arrival, she still fled the room, but the growl was new. Perhaps more significantly, the bells’ resonance floated steady but amorphous (properly so) beyond the reading of the psalm, discernible without strain. This sense of presence extends to the TWO’s handling of the bottom end, which is strong and confident. Where bass notes were previously the slightest bit unsure, the TWO carried them with authority, such as the double thump 25 seconds into "Crazy Baby" on Relish. The low-end foundation on Tilt’s "Farmer in the City" is so emboldened by the TWO that you move from peering into Walker’s chamber of horrors to being locked in there with him. Strangely enough, this is a desirable thing.

There’s a whole slab of presence underneath Portishead's Dummy [Go! Discs 422828553-2], an outright homage to atmosphere. "Wandering Star," in particular, drops anchor, with Beth Gibbons’ vocals flapping way above the surface like the signal flag atop a masthead. Once again, the TWO clarifies the metaphor, adding weight to the anchor and seeming to sink it further below sea level. Also on "Wandering Star," a mid-song musical break of scratching and sputtering is powered by a beating bass heart. Here the TWO’s defined edges lend a definitive "thump" to each heartbeat, as if in the chest of an unfit sprinter.

The double bass on "Nevermind," from the Airto Moreira and the Gods of Jazz disc Killer Bees [B&W Music BW041], first draws attention to itself about two minutes into the track. Its plucks swell in intensity, especially through a run that begins around 4:45 in. The TWO, with its enthusiasm for following a waveform through its circle of life, offers a refreshing reminder that the bass is indeed a stringed instrument and not just a downstairs neighbor stomping around.

Fear of filtering

"Less is more" is closely held dogma among audiophiles, and being closer to the source rarely involves additions to the signal stream. From this axiom stems a well-founded fear of filters and circuits that process the signal in one way or another. But there are alternative views within the congregation. It is empirically measurable, for example, that with a suitable filter water can be "purified" nearly to its most elemental form, perhaps even purer than its source. We agree that water picks up impurities along the way, but we may disagree on whether or which of the impurities are in fact desirable and pleasing or offensive and needless. "Accuracy is unknowable," these disciples might say. Maybe it is, maybe it isn’t, but the Audio Harmony TWO shouldn’t be prejudged on the basis of either philosophy. Instead, we might recall a less lofty principle, that the end may indeed justify the means.

A related sort of filter, a little black box (silver, actually) which begs comparison here, is the Ortho Spectrum AR-2000 Analogue Reconstructor. Comparison is perhaps too direct a word given that the $1500 AR-2000 retails at almost three times the asking price as the Audio Harmony TWO. Still, both inhabit a similar niche -- beyond that of supernatural test of faith -- as harmonic filters. The AR-2000 is said to filter "high-frequency digital noise," which listeners may interpret as a smoothing of the sound. Some have been enthusiastic in their reaction. Indeed, although both the AR-2000 and TWO are filters, they may appeal to very different aesthetic tastes.

Within the same system and on the same passages, the AR-2000 is laid-back where the Audio Harmony TWO sounds forward, adjusting for the fact that the former consumes gain while the latter produces it. Where the AR-2000 takes special care in delicately positioning images, the Audio Harmony TWO expends its effort plumbing for detail and dynamics. Listening to both filters highlights the strengths of each, and the Audio Harmony TWO pushes detail forward, like shy actors in a pre-school play. Edges are defined -- thumps are thumpier, and claps are clappier. The TWO doesn’t round off, up or down. Performers and performances are injected with a modest shot of adrenaline.

And it was good

Without a doubt, my system was a different animal with Audio Harmony TWO in the stable. It was a more spirited animal, vibrant and plucky, though not without the need for occasional discipline depending on what I fed it.

At its $550 list price, the Audio Harmony TWO couldn’t exactly be called a tweak -- this is no bag of sand or inverted cone. More accurately, you might think of the TWO as a universal upgrade for your preamplifier, because really that’s the component with which it shares the most heritage, as a harmonically enhanced gain stage. Value is subjective, but I wouldn’t be surprised if the Audio Harmony TWO lent its charm to a commendable preamplifier more thriftily than would an incremental climb up the preamp ladder.

A converted skeptic makes the most forceful evangelist. What began as fear and doubt -- doubt that this little black box could beautify the temple and fear of being thought a blind fool by the believers -- became redemption.

...Aaron Weiss
aaron@soundstage.com

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