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After an obligatory 24/14 break-in on the desk top, the HQ-1 was ready for the big rig. There it slipped into a competitive group fitted on an Acoustic System HeartSong rack and amp stand consisting of:

• Raysonic CD228 run solo or as transport, then into the
• Meier Audio Corda StageDAC with truly comprehensive cross feed and related adjustments including bypass
• Yamamoto HA-02 or Woo Audio Model 5 fitted with EAT 300Bs or Trafomatic Audio Experience Head One or KingRex HQ-1, all dedicated* headphone amps
• Sennheiser HD800 or Audio Technica W1000 or Beyer Dynamic DT880 headphones
• ASI LiveLine cables and cords, Stealth Audio Varidig digital cable
• Walker Audio Velocitor S passive power bar

* The $4,000 Woo is a full-blown 300B integrated with the added functionality of hi-lo impedance headphone outputs and a custom socket for AKG K1000s. The $975 Yamamoto has speaker terminals but is of such low output power as to make those mostly useless. The €1,190 Head One from Serbia doubles as preamp as does the Headquarters.

Given that all the other amps were tubed designs—5U4G-rectified 6SN7-driven direct-heated 300B power triodes in the Woo; Western Electric 408A pentodes in the Yamamoto; EZ81-rectified 6S45P triodes in the Trafomatic—expectations and predictions would be specific. More on the reality of those in a moment. First, how long do you think the HQ-1 will drive a pair of Sennheiser HD800s once it's been switched off?

30 seconds at full volume. After half a minute, first distortion and attenuation kick in. After one full minute, things get very scratchy and strangulated but signal passes for another 30 seconds until all goes dead. The blue indicator LEDs tie likewise to the capacitor bank without hard separation. They extinguish very much delayed while the caps lazily drain. The effect is mere curiosity but does imply that for the purposes at hand, the KingRex power supply is nicely sufficient.

As one would expect from a transistor circuit optimized for headphones, noise was no issue even over the 100/102dB W-1000s and HD800s. The Beyers at 96dB/250Ω were hardest of hearing in this context, the 100dB AudioTechnicas at 40Ω audibly louder for the same input voltage than the 102dB HD800s at 300Ω. Driver loading included sealed (W-1000) and open-backed. Having multiple loads on hand was advantageous. It allowed cross examinations to arrive at the most likely self sound of the amplifier under review. If four different amplifiers sound consistently similar over each load—and consistently distinctive versus the other three amps—the likelihood is good that the sound commentary captures core qualities which should transfer reasonably intact as a flavor or presentational style regardless of which headphones a prospective HQ-1 buyer might pick.

Some basics first. Headphones run single tweeters without crossovers within an inch or so from the ear. They also present high impedances to the amplifier. Combined, this requires very low input voltages to generate outputs that are perceived as loud. Compare that to speakers with big woofers which sit meters away from the listener. They lose more pressure into the room than what actually reaches the ear. The speaker amp has to work a lot harder on more complex loads and put out a lot more. The output devices of headphone amps meanwhile don't even get out of first gear. They operate in gear minus four if we want to emphasize the point. Now enter tubes. As long as operational noise has been reduced to remain below the noise floor of 'hardwired' listening, the usual bandwidth issues, distortion and nonlinearities we know when valves and speakers intersect need no longer apply.

That's because ear speakers don't even belong into the first-watt brigade. They are part of the milli-watt club. Unlike the vast majority of tube users who listen to regular speakers, headphone listeners get to experience pure 2nd-order harmonic distortion. Pure means without the customary overlays of dynamic compression, obvious lack of woofer control, rolled-off frequency extremes and such which distract from the foundation flavor. These grosser distortion distractions now vanish. The same holds true for the usual transistor advantages of superior bass, crisper highs and better resolution. So... if triodes really are the most linear amplification device known to audiophiles as designers on either side of the divide keep telling us, then headphones enjoy them on their best behavior - with minimum distortion and maximum linearity.

Running comparisons between various tubes and transistors under such idealized condition, what's left for distinctions is mostly the pure harmonic finger print of various output stages operating in low distortion mode. How would that translate? With our quartet of amps, the first observation quickly became that they all operated on the same elevated level. None of these was obviously superior or inferior. Period. No winners, no losers, all were very capable machines and priced in close proximity except for the Woo which is also a first-class 8wpc speaker amp.

The second observation was that pure harmonic distortion as a fine flavor rather than gross liability only affects textures as our perceived degree of tonal girth. If we set up an imaginary horizontal line running through the theoretical center of neutral and then park the polarities of lean/mean and voluptuous on the left and right end respectively, the KingRex expectedly sat on the far left. The Yamamoto occupied the far right. The Trafomatic huddled next to the KingRex, the Woo next to the Yamamoto.

However, it's important to stipulate that the distance between the two poles was a lot narrower than it tends to be over loudspeakers. The reasons for that have already been given. Interestingly, the remaining differences did not operate in the usual climate of subjective temperatures, of cool or warm amplifiers. Texturally leaner by way of the KingRex did not mean cooler. Rather, it only meant crisper, with less stuff around or between the notes. Tonally, the Headquarters was not thinner or flatter. The matter was about textures, about what's apparently on the surface of notes. Second-order tube harmonics only created micro fuzz like fine suede. The KingRex was smooth polished leather instead. Wherever two smooth leather surfaces met, there wasn't the transition zone of suede hairs intersecting. The higher the amount of THD, the longer those fine hairs. It's a somewhat odd visual perhaps but useful enough as far as these things go.

There were related observations. With the Yamamoto's 408A Western Electrics, the harmonics were most keyed in on the midrange to produce the greatest textural weightiness or girth on solo vocals or instruments. As a side effect, on something like the quartet formation of Marcel Khalife's lyrical Caress [Nagam Records, Connecting Cultures], the soloist was more highlighted while the accompanists receded not in placement position but attention priority. The opposite polarity of that effect was embodied most by the KingRex but closely followed by the Trafomatic. Those two possessed a higher degree of simultaneous priority whereby listener attention perceived all four performers equally foregrounded.

Given the far narrower 1-foot stage that exists between one's ears with headphones versus the two to four meter wide stage which standard speaker setups create, there's less psychological effort involved when priority is granted to just a soloist who has the other performers somewhat shadowed along the sides. If one finds the KingRex to approach listening fatigue sooner than the valve amps, it would not be due to sharper transients or less developed harmonics.The real reason in my book would be the greater coincident presence of detail occupying our limited headspace.

In his new Corda StageDAC, Jan Meier's cross feed circuit for headphones and speakers is far more effective than I ever experienced HeadRoom's. The KingRex proved most conducive to the more extreme scenarios of 'wide' cross feed (speakers) allied to max amplitude and max delay times. The greater subtle fuzziness of the Yamamoto and Woo became more echo-y and resonant. Those amps dealt better with lower cross feed settings. As complexity of recorded material increased, the KingRex and Trafomatic had the separation advantage. That could keep greater numbers of performers discrete rather than begin to bleed together. This also related directly to the amount and degree of cross feed they could tolerate.

Sennheiser's new HD800 statement headphones stage noticeably more broadly than many competitors partly because their transducers are fixed farther away from the ears. While it seems kindergarten psychology, the greater resultant headspace quite literally embraces more performers before "things get crowded". While the various tubular actions were audible and appreciated, they distinctly were no prerequisite for full enjoyment of the 800s. I would not say the same for the rather grayer BeyerDynamics. Those ask for —I'd actually say demand—tube fortifications and an extra dose of drive to fully blossom. Perhaps by virtue of its most ridiculously overbuilt power supply for the occasion, the Woo Audio Model 5 was the most appropriate amplifier for these German cans.

The Yamamoto HA-02 was arguably the most contoured amplifier of this grouping. While too linear to be called deep triode—it does not go soft in the extremes—it leans into the general direction in a controlled way and as such was most wonderfully complemented by the AudioTechnicas' voicing to make the most luscious or tonally luxurious pairing I had on hand. The W-1000s lost some of that special magic over the Headquarters. To my ears, they preferred valves. The very resolved Sennheisers were equally at home on all amps. While I could discern the various valve contributions through them most clearly, that triggered no preferences. I could follow Dino Saluzzi and Anja Lechner [Ojos Negros, ECM] over the KingRex without any perceived loss of tone and admire their burnished cello and glittering bandoneon uncut.

Moved to the speaker system, the same held true with the admittedly superlative FirstWatt J2 amplifier. Like its F5 stable mate which I usually run with Esoteric's C-03, the silvery amp with the new Power JFETs in the output stage cottoned to the class A Mosfets in the KingRex Headquarters without any signs of bleaching when the HQ-1 was used as one-input preamplifier.

In that scenario, you'll suspect a nasty ground loop—which a cheater plug won't cure—if you've got the Headquarters set to headphones rather than line outputs. All goes dead silent once the amp properly sees the HQ-1's live line-outs but switching from the 1/4-inch output to the RCAs with the tiny push button on the front elicits a very audible transient. Those averse to such momentary machinations will simply turn the main amp off before converting the HQ-1 from preamplifier to headphone amp with the push of a tiny switch.

The built-in low noise floor of the HQ-1 serves it very well as a big-system preamplifier indeed. While it lacks the final textural suavity of the wildly more expensive Esoteric beast and its Wyred4Sound alter ego, most real-world shoppers immediately appreciate the diminishing percentages at work in any such extreme juxtapositions. Those lucky enough to hear a FirstWatt J2 will additionally appreciate its phenomenal smoothness and minor sweetness. The little which the Headquarters may not provide in that department compared to the big guns won't be missed in such a pairing.

The HQ-1 had no issues driving 4 meters of interconnects. While bigger power supplies make for bigger dynamics over regular speakers, the kind of music I most enjoy lives far more on microdynamic finesse than monster waves. Here I never found the KingRex really wanting. Small boxes, big heart. In conclusion, the two-box Headquarters majors on the kind of unforced natural resolution superior noise floors and non-stressed class A-biased output devices often arrive at. While the transistor virtues of cleanly rendered transients are evident, they aren't overstressed. Tone weight is actually quite higher than expected but the preamp does want to be thermally ready and properly run in. It does sound somewhat steely and flat new out of the box and more restrained before it has reached operational temps (chassis clearly warm to the touch but never more than that). I didn't clock break-in progress but simply left the piece under signal for more than two constant weeks.

Besides the obvious lack of features—no remote, single input, single RCA output—and the nearly magnetic attraction for finger prints thanks to the high-polish black casing, I don't believe anyone shopping in this league can cast legitimate complaints. Naturally, there is competition. As a headphone amp, the Yamamoto HA-02 priced within spitting distance is a very serious distraction. For those who want tubes! with all its popular implications, the Yamamoto is the unequivocal choice at this price. But, it cannot double as preamp. To my mind, the most dangerous competitor is actually the revised Trafomatic Audio Experience Head One. While more expensive, it adds a second input and second output. Sonically, it sits closer to the KingRex than Yamamoto, hence appeals to the same customer. But it does add that small amount of tube bloom and richness which some could find quite addictive once experienced, particularly if their source component is somewhat lacking in that department.

If the HD-800 is one of the three best consumer headphones on the present planet as general commentary and personal feelings suggest, the showing of the HQ-1 with them was perhaps the most instructive of all. It told me in no uncertain terms that given quality ancillaries, the HQ-1 needs no tone help whatsoever even when one comes off some pretty highfalutin gear for context and carries valve-based expectation baggage. Let's talk source then, the only electronic component you must contribute to turn the Headquarters into a complete headphone system. The Raysonic Audio CD228 is a virtual stand-in for my customary Esoteric/Yamamoto digital combo but does pull ever so slightly ahead. That makes it a very serious front end indeed, a new game for Raysonic. It's also a mondo while perhaps unrealistic mate for the HQ-1. If you can reach for something like the CD228 or one of its lighter 128 or 168 siblings, the KingRex should be the end of the road even for high rollers.

And yes, after the CD228, the far more reasonable April Music Stello CDT-100/DA100 Signature combo did promptly telegraph as a step down. Not as pressurized from within as the Raysonic with its truly prodigious power supply, dynamically paler and painting with a simply weaker color palette, I found the outcome a bit stark when fed into the Beyer DT880s. This isn't dissing the Germans, just adding data points to paint a fuller picture.

Given that the Yamamoto HA-02 has been my favorite headphone amp since my discovery of it a few years ago; given that the Trafomatic Head One is its full equal, albeit in a more linear, less midrange-centric way while adding very compelling preamp functionality with a subwoofer output and a second input to be quite more versatile; and given that the Headquarters HQ-1 clearly performs on their level while offering a distinct sonic flavor - it's clear that KingRex has a winner on their hands that's mature out of the gate. The amp isn't warm per se but does have a tone density that's indeed very similar to what we know from tubes. The difference is textural. Tube THD with its more water-color transitions is replaced by crisper starker cleaner outlines for less connective tissue but more potent separation.

In the end, that's what it boiled down to. Most the other audiophile attributes had been equalized or linearized amongst the four amps I had for comparison. The usual distinctions of more or less bass, midrange, treble—add to this list at your leisure—were for most intents and purposes irrelevant. Yamamoto excepted for its obvious voicing, it was down to a fine flavor or aroma where the HQ-1 focuses on articulation, definition and crispness with great solidity of tone. While costlier than the company's initial offerings, KingRex fully delivers the higher standards which the new sticker would demand. All is as it should be and KingRex now plays in the bigger leagues. Welcome to da club!

Quality of packing:
Very good.
Reusability of packing: A few times.
Condition of component received: Flawless.
Completeness of delivery: Perfect. Includes power cord, power umbilical and in a separate carton, the pointy footers with adjustable tips.
Human interactions: International sales manager Christine Wu very responsive.
Pricing: Good value for money.
Final comments & suggestions: Class A circuit sounds better after about 30 minutes of warm-up time and the machine needs about 200 hours of break-in. High-gloss casing very susceptible to finger prints. In preamp mode, functionality is limited to single i/o ports.
KingRex website