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Reviewers can never please all. Some insist that components should only be reviewed on their own merit. Comparisons are meaningless. They're capricious, booby prizes by writers incapable of judging against an absolute reference. Others find comparisons most useful. For them the opposite approach hangs in meaningless limbo. Then there are those who think reviewers inept or corrupt. This review doesn't worry about them or the first kind.

That's because I believe more data points to be more—rather than less—useful. That's particularly relevant when you can triangulate listed comparators elsewhere. It becomes a reader's version of networking. Comparators for this review were the Burson Audio HA-160 and KingRex HeadQuarters whose feature reviews are packed with comprehensive context. I also had the new NuForce HDP on hand to mix things up further. Chief headphones would be my Sennheiser HD800 rewired with Ken Ball's excellent—and mandatory—custom cryo cable. From the six headphones I own, the 800s are the best. For drive, the equally rewired AKG K-702 are my toughest customers. They'd too make appearances. My AIFF-loaded 160GB maxed-out iPod Classic had recently gone on the fritz. Partial hard drive failure. It was at a Lausanne Apple dealer for resurrection. Instead of running the iPod digital direct through my Peachtree Audio iDecco's fixed analog output as planned, I leashed up Raysonic Audio's CD228 for the serious part of my auditions. Comparing the Raysonic's own D/A converter and analog output stage to going digital out into the iDecco's Sabre DAC then out through its fixed outputs, the CD228 won. So that became the default source for the following commentary.

Concerto vs. Burson Audio HA-160
: Functionally, the Concerto was the more advanced. Its lo/hi gain function allied to 0.7dB attenuator steps created a broader adjustment range than the fixed 2dB steps of Burson's custom solution. The latter becomes particularly limiting with higher source voltages. While the Raysonic adopts variable gain in the digital domain, its 4.7V in fixed mode reduce useful range to a mere few clicks. The Burson will be useless for ultra-efficiency ear-canal headphones. The Concerto meanwhile coddles them. Then it throws in crossfeed. The Burson retaliates with lo/hi impedance ports. On enclosure build, the Burson's 6mill panels beat anything in this sector. Whether that's important is a different matter but on raw vault pride, the Burson is boss.

Over my phones, both were dead quiet
(even though my HA-160 loaner has ground-plane issues to often cause ground loops without a cheater plug - supposedly addressed since my review). Both exhibited what one thinks of as iron-fisted driver control - bass balls of brass, jumpy and long-arced dynamics and very high resolution even at low volumes. The most apparent difference concerned the handling of transients and, relatedly, overall textures. The amp from Oz was warmer, not as lit up on top and as a result, less blistery on guitar arpeggios, less spicy on Cuban brass and less angular on rhythmically peppery fare.

On subjective articulation—that sense of lithe finesse that peels out individual strands—the Concerto was keener. Texturally, the HA-160 felt drier, less illuminated. Its particular kind of warmth is most decidedly not valve fuzziness from octave-doubled harmonic distortion. Instead it seems to be an intrinsic quality of their discrete modules - faint parts signatures. The Australian's insistence that op amps suck falls apart of course when confronted by something like Jan Meier's Concerto which embraces them and sounds no worse for it. But there were clear differences. Unless we are the designer, it's simply impossible to ascribe differences to specific circuit or parts choices.

Having lived with both amps for a while, I couldn't fault either. I own the big Woo Audio Model 5 with dual EML 5U4G rectifiers, 6SN7 drivers and 300B output bottles; the Trafomatic Audio Experience Head One; and the Yamamoto HA-02. Those all use tubes. My sonic references are thus evenly split. To find any headphone amp compelling these days, it has to carefully walk down center aisle. As transistor units, both Burson and Corda avoid the type of silicon signatures valve lovers shy away from.

That said, the more piquant handling of the leading edge displayed by the Concerto was more transistor typical than Burson Audio's. Over my cured Sennheisers, I found the embedded sense of energy compelling. With their native forward treble and tendencies to brightness, the HD800s without a quality after-market wire harness would most likely not be my first choice over the Corda. The rather darker triode-esque Audio-Technica Raffinatos meanwhile are tailor-made. Ditto the ballsy semi voluptuous Grado PS-1000s. For triangulation purposes, this should suffice.

Concerto vs. KingRex Headquarters
: On build, the KingRex with its sculpted front panels and two boxes was the more luxurious of the two. On features, it added a preamp output, a function in which it is surprisingly adept. Then it subtracted the crossfeed circuit. Its Alps pot had as broad a useable range as the Concerto, just no steps. On decipherable self noise and over my type of big headphones, it was just as absentee.

Sonically however, the Concerto's noise floor seemed lower yet. This had nothing to do with hum or hiss. Neither suffered any. It had to do with contrast ratio - the amount of pop or lock soloists had over against background accompaniment; and that accompaniment over against its surrounding space. In headfi speak, that's blackground. Of these three amps, the Concerto was the blackgroundiest. That's why subjectively, it also seemed the most resolved. In a very faint hommage to my Esoteric C-03 preamp with its very flexible gain settings (0, 12dB and 24dB), I also developed the notion that the Concerto in its high-gain setting sounded a tad fuller and richer. This was subtle. Still, it eventually became my default setting.

Overall this pairing was closer than the previous. Once the class A KingRex had thermally stabilized, beyond the first few seconds when one keys into subtle tonal color shifts, I predict that most would have a hard time keeping these apart. The Burson Audio meanwhile would be pinned easily. It sounds more damped or relaxed depending on whether you view that quality as liability or asset. On close-miked Ethnic pop like Sezen Aksu for example—or George Dalaras with a big bouzouq ensemble—both KingRex and Concerto could bare their fangs and show some edge. Edge ain't bad. Edge is an intrinsic part of musical excitement. It's objectionable only when it turns to etch. Each listener calls that transition differently. On the inherently lit up Sennheisers, I didn't find the KingRex or Corda objectionable. Even so, I remained aware of a tendency particularly at stouter levels. It's relevant to personal sensitivity, the 'phones you want to drive and how loud you generally listen. Higher levels make this more pronounced (liability) whereas very low levels benefit from extra intelligibility (asset).

Concerto vs. NuForce HDP
: The $449 switch-mode powered class D NuForce books neither the class A cachet of the KingRex and Burson or the mondo capacitive filtering of the Corda. But it does double as preamp. And over the KingRex which does too, it adds inputs. And to be shameless, it throws in a USB DAC borrowed from the company's CD player. On features, it outshines this lot - including little things like a 1/4"-to-mini adaptor. Cosmetically, it's the NuForce Icon extrusion with rounded corners that can either go sideways—simply stick on rubber bumpers—or upright in the provided retainer. On gain, there was more than enough to redline the AKG K-702s. On noise, nothing.

This sonic comparison was unexpected. The NuForce was the minorly sweeter and silkier of the two but didn't come second on snarl when appropriate. Forget about the company's 1st-gen hyper-realist Pandora sound with 3D glasses. This wasn't that. The Concerto in fact was sharper on the leading edge. The NuForce was closer to the Burson's smoothness yet maintained the treble brilliance and excitement of the other two. With its own feature review still out, I'll leave details save to predict that this dark horse seems set to upset the segment.

On crossfeed: As Jan Meier's description predicted, the Concerto's implementation is far less complex than the StageDAC's. As such it's also rather less potent. The desirability or necessity of the Concerto's implementation remains questionable. On some material, you can't hear it at all. On some, you can and it's a welcome increase in density. On some, you notice a very fine blurring or smudging instead. That's a 66% failure rate. I of course never thought the headphone experience strange or tiresome in the first place. To me it's simply different from speaker listening. Neither sounds like the real thing but both have their own very merits and attractions. Some people however do seem terribly put off by the in-the-head perspective and harder panning of headphones. They could be rather more sensitive to and appreciative of this feature. Personally, it wouldn't be decisive.

Decisive: Given my familiarity with this category and price range, the Concerto seems highly competitive. Two key selling points are exceptional noise performance; and a very flexible gain/attenuation scheme which accommodates headphones of very disparate sensitivities. On nits, I found the on/off on/off LED adjacent to the pot utterly redundant. This LED can't be used to repeat the same setting from one day to the next. You'd have to actually count how many times the LED switched on and off from mute to be sure. Why is it there? I feel similar about the other five. Since there's no remote, you must sit close enough to operate the volume manually. That means you're close enough to see where it sits and whether the gain switch is in the hi/up or lo/down position. The LEDs are somewhat frilly.

Looking at the internal parts density and serious capacitive filtering meanwhile, one's money is fairly spent and well invested. This isn't a mostly empty glitz machine where an inner iron plate bulks up the weight to impress the innocent. Sonically, the obvious goal was high resolution, i.e. very low noise and low distortion. With tendencies, the Concerto is on the lively brighter side. As you'd expect from opamps barely asked to put out, linearity is very high as are dynamics. Clearly Jan Meier knows his op amps and has picked one that 'comes on song' at low-level currents. There's nothing lean or whitish here but the overall color temperature is a tad cool.

Conclusion: Headphone amplifiers are a very interesting sub species. Versus speaker loads, headphones are sissies. Any proper output device mostly idles to sound its most linear and best. The great challenge is noise and having to reach max resolution at very low output currents. Mastered, the most varied of circuit choices and output devices will sound more similar than not once we get into best of class. Distortion lowers, load impedance interactions are diminished and the amps operate within their sweet spot. It's fitting then that the above comparisons between top specimens weren't spread wider. Had I brought in my $4.000 Woo with $1.000+ of designer glass, they would have been. Overkill power supplies for any audio occasion do that. The Woo's 8 watts are meant to drive speakers. For headphones, that's excessive. It costs dearly—disproportionately in fact—but does pay off.

Jan Meier's Corda Concerto amplifier is purely dedicated to headphones and one source. It won't double as preamp. It offers nearly extreme resolution thanks to truly massaged noise floor performance. It's on the incisive, energetic and illuminated side of the Tao and as such, not a top choice for bright, forward and potentially steely loads. Drive and gain seem commensurate with anything consumer hifi might throw at it. Quite unlike the vast majority of headphone amps, the Concerto was tweaked to accommodate all sizes. It does standard efficiency 2-inch plus drivers on the ear and ultra-sensitive tiny units in the ear canal. The volume control range and its small steps plus two cleverly chosen gain settings are commensurate with either. In a full-size rather than portable design, that's what sets the Concerto apart. It's the perfect anything-goes dedicated headphone amplifier.

Quality of packing:
Reusability of packing: No issue.
Ease of unpacking/repacking: A cinch.
Condition of component received: Flawless.
Completeness of delivery: Perfect.
Human interactions: Good.
Pricing: Sino assembly and direct sales mean high value.
Meier Audio website