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Reviewer: Srajan Ebaen
Source: Raysonic CD128 [on extended loan]
CD Recorder: Olive Symphony with Red Wine Audio battery mod
Headphones: audio-technica W-1000
Cables: Crystal Cable Ultra loom [on extended loan]
Powerline conditioning: Furutech RTP-6 passive
Review Component Retail: $975

It's no secret. I greatly admire Japanese tube audio designer Shigeki Yamamoto. His A-08S single-ended 45 amplifier has graced my reference system since its review. It remains one of my favorite audio acquisitions. It doesn't just sound spectacular. It also embodies and exudes tell-tale evidence of maverick artisanship at the very highest level. In short, whatever Yamamoto can't outsource to satisfaction gets fabricated in his own machine shop. Items like Yamamoto's custom Teflon tube sockets are sought-after kit with other upscale valve electronic makers. His custom Cherry-with-resin composite shows up in another maker's $20K Signature amp. To own one of Yamamoto's fairly priced creations is the closest most blue-collar music lovers will ever get to calling a hand-crafted Stradivarius violin or Herbert Wurlitzer vintage clarinet their own. This tie-in with famous musical instruments isn't fancy smoke. Yamamoto Sound Craft is squarely in the musical instrument business. They simply cater to those of us who don't play our own instrument but enjoy hearing others play theirs. Audiophiles. You and me.

When news of Shigeki-San's new headphone amplifier rushed down the East-West pike, I immediately contacted the maestro through his website. Time to place an order. Returning a review loaner to Ono City, Hyogo Prefecture simply wouldn't do. After my stellar experiences with the 45 SET, I knew full well I'd have to own an HA-02. For good. You might call it blind risk. I called it open-eyed certainty. Even my audio-technica W-1000s were twitching in anticipation. Off to the bank it was for a wire transfer while I consigned myself to waiting for the phone call that would eventually alert me to pick up a package from Japan at one of the various check points which Cyprus couriers use after the main shippers must relinquish their goods at Larnaka airport customs and the island's many subcontractors take over. (Mind you, some of their dingy back-office locations could double for WWII Berlin spy movie rendezvous spots.)

Sporting the firm's signature resin-impregnated Japanese Cherry top and Ebony corner columns doubling as footer standoffs and upscale custom parts below deck, the HA-02 sports two NOS Western Electric WE408As under a gold-plated decor bridge. By virtue of having been manufactured en mass for high-frequency telephony amplification, these small-signal bottles are reportedly in abundant supply even today (and allegedly good for far longer duty cycles than average audio tubes).

Western Electric's on-line PDF reproduction for the 408A/6028 data sheet is dated 1953. Bell Labs AT&T features as the noted recipient and production of this tube through the 1940s was, not surprisingly with a corporate account of this magnitude, a major enterprise in Allentown. This 7-pin miniature pentode with indirectly heated cathode measures all of 1¾" from pin ends to nipple tip and 1½" without pins. Besides WE, NOS tube sellers also list Sylvania and ECG Philips USA variants. Cheaply.

The HA-02 wires it as a feedback-less pentode which benefits from ultra-quality in-house-wound transformers adapted from the accoladed A-08S. 50-ohm headphone and 8-ohm speaker secondaries connect to the front-mounted ¼" socket and rear-mounted speaker binding posts. Delivering 300mW @ 50 ohms at the former and a mere 240mW @ 8 ohms at the latter, a speaker driven from the HA-02 will have to be efficient and used in the extreme nearfield, say in a desk top PC setup. The HA-02 ships with an audio-technica designed interconnect terminated on the source end with a mini stereo jack. Hello iPod or equivalent.

Gain of this headphone amp is 9.5dB into 50 ohms, 1.5dB into 8. Frequency response is 30-21,000Hz and 45-17,000Hz respectively. Noise at the ¼" terminal is given as 100 microvolts. Everything about this device spells high class and the promise of noise-free, high resolution, ultra musical thermionic headphone addiction.

And in case you're wondering - yes, the nomenclature's 02 designation suggests a preceding 01. Indeed, there was. It ran two 3S4/1S4 bottles connected in single-ended non-feedback mode for 180mW of max output. Today's successor, despite its sub 1-watt power output, thus rather grew in raw oomph. Considering the very short distance sound travels from ear cup to inner ear with headphones, these power ratings aren't as microscopic as they may seem on paper. Especially when mated to high-efficiency 'phones like my audio-technicas.

Then the phone rang: "You've got a package from Japan." I felt like a kid at Christmas.

The piece is even prettier in real life than any photos hint at.

Different from my A-08S is the power switch. Rather than illuminated itself, a light source has been placed behind the top-mounted decal to make visual operation more subtle still.

Flipping this pup on its belly and loosening 10 screws showed the insides.

High class just as the external cosmetics - and rather beaucoup iron on board for the tiny output voltages at hand.

R-core transformer and turret connections for superior joints.

Speaking of superior, check out the fit'n'finsh of the turned volume knob with its little detent.

The single-stage HA-02 is an all'round beaut. Seeing one is to want one. I'm looking at this thing right now. I'm still wanting. And I already own it. This is quite the deal - a sharp dresser with flair. Gain on my audio-technicas is such that 9:00 o'clock on the dial warrants no further twist for stout playback levels on most CDs, with 10:30 - 11:00 the ceiling on albums with a low median level. Background noise? None. The HA-02 is dead quiet just as it should be.

Sonics are unlike anything a pop quiz would predict for a tube amp. The HA-02 is like water - ultra-transparent and essentially absent as a playback device. How often have we heard that no audio amplifying device is as linear as a triode only to realize that once coupled to real-world loads, linearity goes to hell and back in the toilet? The only listeners to know just how linear and dynamic triodes really are will be those who use single-ended feedback-less valves in their respective entry ranges of available output power. Connecting a triode to a single tiny -- and naturally crossover-less -- driver in a headphone prompts average playback levels in the milliwatt sphere. That's where triodes rule and the Yamamoto device proves it brilliantly.

Listening sensitivity diminishes over the course of a session. That's why movie soundtracks get louder towards the end - to make up for this loss. The HA-02 compelled the opposite reaction. I kept turning it down. The music seemed to get louder as I advanced from track to track. Curious about why that would be so, I closely inspected the experience between and behind my ears. I soon realized that the reason for the unusual intensity had to do with weight. It's customary to talk of bass weight with endowed amps or speakers. We all know what's meant by that. How often has this descriptor been applied to the midrange and lower treble, however?

Enter the HA-02. The amount of weight and density it projects on the vocal range is unusual to say the least. This is different from the unnatural energy of an elevated presence region and thus suffers none of the eventual fatigue or heat endemic to such voicings.

It's not the case that bass is lightweight or unduly shy either which could account for a perception of midrange prominence. And to be sure, it has nothing to do with prominence such as we usually understand it. Hence my choice of weight for this phenomenon.

Related to it is color temperature of tonal hues. The palette from which the Yamamoto draws is incredibly rich and saturated yet perfectly coincident with the aforementioned water-like transparency. It's the polar opposite to the deep-triode type of thickness which is actually opaque. The Yamamoto deserves its own moniker like deep triode - but pointing in a different direction.

A related aspect I saw very clearly during a late-night session exploring the Cracow Kletzmer Band had to do with dimensionality. This was exceptionally highlighted on their superior recordings. You've seen plain type face in print, say as a header in an ad. You'll also have seen such type face rendered with a so-called drop shadow behind it. This insinuates dimensional depth as though the type was floating on the flat page. The next level beyond that illusion is called embossing. There the type itself gets shadows to create relief, facets and angles on the font. Beyond that is the embossed font plus a drop shadow.

As the crude graphic example shows, the illusion of three-dimensional space heightens in steps. And that's exactly what the HA-02 does. It's easiest to appreciate that in all its glory on material that's not too crowded with intersecting lines. Then you can fully see how individual tones interact with space, are surrounded by 'drop shadows' and enjoy textures on their own surface. You can even tell what distance those shadows/reflections are from the font/notes to get a clear sense for where the paper/boundaries are.

Exploring new music I'd recently bought, I would set the volume based on the first track not knowing what to expect down the road. Peaks invariably compelled me to reset the volume down a notch or two, evidence that the Yamamoto's dynamic range is very padded. Now combine these various attributes -- heightened dimensionality, extreme weightiness in the vocal range and lower treble, saturated tone colors, accelerated dynamics and extreme transparency -- and you've got the Yamamoto HA-02 pegged. Real Triode might be a suitable tag for it. These are all qualities you get to various degrees with SET amps and copasetic speakers. I myself do with the Zus and Yamamoto A-08S. But I dare predict that the extent to which this headphone amplifier epitomizes the breed and explores its outer limits transcends what most will have heard from regular speaker amplifiers before.

In fact, the HA-02 with a pair of superior headphones could be slightly preferable to the A-08S with speakers. That's because the Yamamoto is way overbuilt for its intended headphone-drivin' task and, as a high-gain pentode design, get's away with a single stage. As a quasi linestage device, it is presented by a load that doesn't have its triodes strain. Instead and like flowers, they stand erect in a wind-still niche, blossoms open, fragrance undiluted by gusty conditions. In that sense, it's an idealized greenhouse scenario. Conversely, the speaker variable, how it interfaces with the amp plus unpredictable room interactions could be anything but ideal. I've owned my audio-technica wood-cup 'phones for years. Truth be told, I didn't know they were this good. No headphone amp before has quite maxed out their potential to this degree. That's a lovely bonus for me. Never mind that the two together have a very similar finish. How would the Yammy work on 32-ohm Grados and 300-ohm Sennheisers? I don't know. I've long since sold my HD-650s. For my tastes, the W1000s ran circles around 'em and were far more comfortable to wear. The Sennheisers could be somewhat of an impedance mismatch on this amp but I'd have to hear them to know for sure.

I said earlier that the Yamamoto HA-02 is essentially not there. Neither are inductive/magnetic volume controls. But they don't do this. Not even close. It's a delicious oxymoron. The Yammy doesn't sound at all like it's additive. The music is so intense that the usual playback artifice gets completely overpowered. But I've heard plenty of so-called neutral headphone amps that couldn't touch the intensity factor of this piece. Which renders it something other than neutral, doesn't it? Or were the other amps somehow subtractive by diluting the presence degree? Hence oxymoron. It's impossible to suss out true north except to say that if the Yamamoto is additive, it goes about its job in such a way as to not diminish resolution or jump factor. There's no tone painting that renders the photograph of the real somewhat abstracted. Quite the contrary. It seems more real. This includes how it fills out the airline pillow soundstage that wraps around the neck behind the ears. Even staging becomes more robust and substantial. As far as I'm concerned, the HA-02 is an A-08S for headphones. The sonic family resemblance is uncanny. With the amount of ink our site has bestowed on the 45 SET, that's a wonderful thing indeed. And unlike with the A-08S, there's no painful brightness period during break-in to suffer through.

In conclusion, the HA-02 mirrors transistors in how linear it sounds and how detailed against a very low noise floor. But it's triode through and through in its staging, layering, coloring and microdynamics. Considering how intimate an experience headphone listening is, you really do want the very best this close to your ears. For the 40-ohm ATH W1000 "affordable luxury" 'phones, the Yamamoto is a match made in the Japanese heavens. Christmas indeed.

PS: Readers familiar with my prior endorsement of the Eastern Electric MiniMax CDP's headphone socket for the W1000s may wonder how it compares. I sold the MiniMax before I left the US so that's a comparison I can no longer make. I'm reasonably certain, however, that the Yamamoto rather goes beyond. What I can tell you for sure is how it compares to my AKG K-1000s with their hard-wired Stefan AudioArt tail run off a Nelson Pass FirstWatt F1 preceded by a Wyetech Labs Jade preamp. The Yamamoto/W1000 combo is far more psychedelic. Its contrasts and tone colors are like Panasonic's BlueRay demo I witnessed at the Poland Audio Show. By comparison, my other setup is leaner and whiter - very accurate, very resolved, an ideal monitoring tool yet with all audiophile complaints removed due to the replacement wiring and the tube preamp preceding the current-source amp. The AKG rig is day-light business, the audio-technica setup a night-time affair. And having the two stimulates and satisfies both brain hemispheres. But for pleasure listening, it's a beyond-brainer. The Yamamoto system rules.

Manufacturer's website
German distributor's website
US distributor's website