Reviewers' ChoiceEsoteric A-02After listening to Esoteric’s A-02 stereo power amplifier ($17,600 USD) for a few weeks and figuring I’d better begin my review, I grabbed the model’s marketing brochure. But aside from a few basic specifications, most of the brochure is dedicated to flowery audio language that’s not only meaningless, but poorly translated from the Japanese. An example: We are told that the A-02 will provide "a musical experience featuring beautiful resonance swelling with the reverberation of crashing waves and vitality." Was I reading a brochure for an amplifier, an energy drink, or a vacation paradise? It was hard to tell.

But surely, the brochure had to contain some meaningful information I could use. And it did. One passage cryptically states that the A-02 "is infused with knowhow gained from professional studio devices based on the unique Master Sound Works concept. We pursued sound quality befitting original master recording playback through collaborations with studio engineers . . . in professional applications."

I asked Tim Crable, Esoteric’s US Director of Sales, what this actually meant. He told me that in 2009, Esoteric was approached by Nittobo Acoustic Engineering Co., Ltd. (NAE), a Japanese company that specializes in the design and construction of sound studios, listening rooms, and acoustical laboratories. NAE had been using Esoteric’s A-80, a 200W monoblock, in the development of its own products, and really liked it. In fact, when NAE needed a mono amp to complement its system of custom-made NES studio monitor speakers, it asked Esoteric to build it, based on the design of the A-80. Esoteric accepted NAE’s offer.

After nearly a year of development, Esoteric introduced the NES400ES, a 200W monoblock amplifier designed exclusively for NAE. This model proved so successful that Esoteric began selling it worldwide to other professional customers: studios, sound laboratories, universities, and other organizations that require high-power amplification.

After the debut of the NES400ES, a Japanese recording studio, Sound Inn, asked NAE if it knew of a high-power stereo amp it could use in one of its studios. NAE asked Esoteric to manufacture a stereo version of the A-80 for Sound Inn. The result is the Esoteric A-02.

Features: power, headroom, a power plug support bracket

Like its monoblock cousins, Esoteric’s A-80 and NES400ES, the stereo A-02 operates in class-AB, and is rated to output to each channel 200W into an 8-ohm load. Granted, some amps offer as much as 1000Wpc, but 200W is certainly enough to characterize the A-02 as a "high-power" amp.

Also like its cousins, the A-02 is claimed to "double down": Its 200Wpc output increases to 400W when the impedance is halved to 4 ohms. And in bridged mode, the A-02 is claimed to deliver 800W into 8 ohms.

According to Esoteric, the A-02 has a number of design features that make it stand out from the pack. First is its transformer. The transformers of many amps, including Esoteric’s A-03 50W class-A stereo model, use one toroidal core for the input stage and two for the output stage for each channel. Each of these stages converts alternating current (AC) to direct current (DC) for use by the amp, albeit in different currents: one high, one low.

The A-02, however, uses one small toroidal core for the input stage power supplies and one large one for the output stage. Esoteric states that this configuration is optimal where, as in the case of the A-02 and its 800W potential, high current is required. This is because when two donut-shaped cores are placed in a square box, the effective areas of two small cores, and thus their ability to supply current, is less than if one large core is used. Conversely, the A-03 uses two cores for its output stage. According to Esoteric, this is due to it being a class-A amplifier that produces 200W in bridged mode. It therefore does not need to generate as much current as the A-02. Further, Esoteric advises that the use of two cores results in better channel separation.

Second, to match the signal level coming from the source (e.g., a CD player or computer server) to the power requirements of the speakers, the A-02 employs only two gain stages. This results in very short signal paths, in contrast to some amplifiers that use three or even four gain stages. The more stages of amplification (and thus the more electronic parts required), the greater the possibility that signal noise will be generated. According to Esoteric, the use of short signal paths also improves stability of the amplifier, and allows the A-02 to operate with minuscule amounts of negative feedback.

Note that the shortest signal path, and thus the theoretically quietest operation, would be achieved by employing only a single gain stage. Esoteric states, however, that such a design tends to produce signals that are nonlinear in that they suffer low-frequency deficiencies.

Third, the output stage for each of the A-02’s channels contains five linear amplified power transistors (LAPTs) mounted in a parallel push-pull configuration. As each transistor can generate a whopping 17A of continuous current, the A-02 has the ability to move a total of 85A through each channel. What this means is that the A-02 can handle speakers with very low-impedance dips and are therefore difficult to drive. It also means that the amp is likely to have a lot of headroom. Amps with insufficient headroom can either trip their internal protection circuits, or sound muffled or constrained when called on to reproduce music that includes wide dynamic swings.

Finally, Esoteric states that the A-02’s capacitors, transistors, and resistors are hand-selected based not on specifications or reputation, but on how they sound when used in this particular amplifier. According to Esoteric, this greatly improves the A-02’s sound quality, as well as its ability to remain extremely linear while providing high power.

Esoteric A-02

The A-02 has a damping factor of 1000. This number indicates how well an amp can theoretically control the movement of the speakers’ drivers, and thus their output. The total harmonic distortion is rated at 0.009% (1kHz, 8 ohms, at rated output).

The A-02’s case measures 17.5"W by 8.6"H by 16.9"D. It has aluminum front and top panels that are 5 and 20mm thick, respectively. The steel bottom plate and inner compartment walls are 5 and 2mm thick, respectively.

On the A-02’s clean front panel is only a power button. This is illuminated by colored LEDs that indicate the amp’s status: active or standby. The rear panel is slightly busier. It has selectors for input (XLR/RCA) and output (bridged mode or stereo); XLR and single-ended input connectors; WBT-0710Cu Nextgen speaker terminals that accept bare wire, spades, or banana plugs; a signal ground terminal; and an IEC power inlet.

Anyone with experience of Esoteric gear is familiar with the build quality of the company’s products, which is impeccable. Fit and finish are museum quality and practically scream luxury. Not surprisingly, the A-02 is heavy. It weighs 92 pounds and is supported on four proprietary-design steel feet.

Other than your $17,600 amplifier, inside the shipping box you’ll find a power cord, felt pads that can be placed under the A-02’s feet to protect a shelf or rack, and a feature that’s nothing short of pure genius: a small "power plug support bracket." This is a metal shelf that screws into the back of the unit, just below the IEC inlet. It ensures that the plug sits easily in the IEC socket without subjecting it to excessive strain. If every component had this clever device, the world would be a better place. Well, at least the backs of my electronics would be.

Setup: the lower the better

Amplifiers love being placed near the floor, so I put the A-02 on a Custom Isolation Products amp stand. I also used a set of Synergistic Research MIG footers in lieu of the A-02’s steel feet. In my experience of a number of Esoteric components, the steel feet attached to the units work well; the MIGs work better.

After screwing the power plug support bracket into the back of the A-02, I connected the amp to my Synergistic Powercell 10SE Mk.II power conditioner via a Synergistic Hologram A power cord. I then connected it to my YG Acoustics Kipod II Signature speakers and my Esoteric C-03 preamplifier via Synergistic Element Copper-Tungsten-Silver speaker cables and interconnects, respectively.

When pushed, the A-02’s power button blinks blue for a few seconds, then glows steadily, which indicates readiness for play. If the blinking doesn’t stop, this may indicate a short somewhere in the cabling. Blue and purple blinking indicate overheating. While in my possession, the A-02 worked flawlessly.

Performance: bringing back sexy

The A-02 superbly delineated voices and instruments on the soundstage while sounding detailed, refined, and translucent. Tonally, the A-02 was utterly neutral. The sound of Pepe Romero’s "Zapateado," from Winston Ma’s This Is K2 Sound! (CD, FIM K2 HD 078 UDC), was "wet" through the A-02 -- the reverberation of the flamenco dancer’s shoes striking the floor and ricocheting off the theater walls seemed endless. In Annie Bisson’s "Do What You Please," from Fidelio Reference 2 (CD, Fidelio FACD910), the acoustic guitar that accompanies Bisson’s voice spanned my listening room with remarkable richness and body. Just as impressive, these qualities were not lost at low volumes.

With Dance of the Reed Flutes, from Tchaikovsky’s The Nutcracker, with Michael Tilson Thomas conducting the Philharmonia Orchestra -- an excerpt found on Greatest Hits: Flute (CD, Sony Classical 66703) -- the A-02 rendered the flutes with Ferrari-like sensuality and emotional nuance. This despite the fact that, unlike the fabled Italian sports car, Esoteric gear does in fact have a reputation for being well made and reliable. A steady stream of components has passed through my listening room over the years, including some Esoteric models, and while I’ve experienced a surprising number of equipment failures and associated headaches, no Esoteric product has ever done anything but work flawlessly here. Of course, professional audio customers are notoriously demanding when it comes to reliability. The fact that NAE and Sound Inn use Esoteric amps speaks volumes.

So far, so good. However, I would have been remiss had I not tested the A-02’s raison d’être: to provide enough power and headroom to handle wide and sudden dynamic swings. My go-to test disc for headroom is Orff’s Carmina burana, as rendered by Donald Runnicles and the Atlanta Symphony Orchestra and Chorus (SACD/CD, Telarc SACD-60575). O Fortuna, the opening and closing chorus of that "scenic cantata," as Orff called it, is punctuated by the sounds of a bass drum hit extremely hard. The effect is so striking (so to speak) and so sudden that it causes many amps to strain as they almost instantly approach their headroom limit. This was not the case with the A-02 -- it not only more than kept its composure with this track, it nonchalantly acted as if it could call up even more power reserves if asked.

Esoteric A-02

The A-02 sonically wowed me. Yes, some very expensive components may sound (or at first blush seem to sound) faster and even more translucent than the A-02. However, after my honeymoons with many of those other components, I typically began to crave something a bit more rich and full, and less aggressive.

Putting aside the question of the A-02’s quality of sound, I couldn’t help asking this one: Who really needs the abundant amount of power and headroom the A-02 offers? The question is reasonable -- the A-02 costs $17,600, after all -- and is particularly worth asking in light of the existence of Esoteric’s own well-received A-03. That amp offers 50Wpc of class-A power for $12,900 -- $4700 less than the A-02. Also, the A-03 runs in pure class-A. Price considerations aside, some audiophiles would never consider purchasing any other type of amplifier.

The answer to that question will primarily depend on the size of the listening room and the type of speakers used. Speakers such as the Magico Q5, the Infinity Kappa 9 (aka the amp killer), or any of the old Apogees require big, beefy amps with lots of watts and headroom to realize their full potential. For those speakers, something like the A-03 simply won’t do; I’d recommend the A-02.

On the other side of the spectrum are speakers such as the YG Acoustics Kipod II Signature, which I paired with the A-02 in my listening room. The Kipod II is moderately efficient, and has a very benign impedance curve and powered woofers. As a result, there may be no compelling need to spend the extra cash for an amp with the A-02’s gravitas -- the A-03 would do the trick rather well.

Perhaps in the middle are speakers such as MartinLogan’s Summit X, which I also listened to with the A-02. That speaker, too, has powered woofers; strictly speaking, you don’t need a monster amp to drive it. Nonetheless, electrostatics such as this often have challenging impedance curves. I felt very comfortable driving the Summit Xes with the A-02.

Finally, I wouldn’t let the fact that the A-02 runs in class-AB bother me. After spending a number of months with it, I think even purists would be surprised at how close it sounded to the A-03. Also, despite what purists say, class-AB amps like the A-02 often have energized leading edges, and a microdynamic liveliness that can greatly benefit many speakers.

Don’t forget that class-AB amps generally run cooler than their class-A kin. This can be an important distinction for some, especially those who live in warmer climates.


I compared the Esoteric A-02 with my resident amp, Bryston’s 6B SST2. At 300Wpc, the Bryston is also high powered. Of course, at $7995, it’s less than half the price of the A-02. Also complicating the comparison is that the three-channel Bryston must drive one more channel than the Esoteric. These considerations aside, the Bryston, like the A-02, proved neutral in tone. As a result, the sounds of the two amps were more similar than different.

Even so, they had their differences. For one, the A-02 created a soundstage that was larger and wider than the Bryston’s. And while the A-02 placed that stage just slightly forward of where the Bryston did, neither stage sounded exaggerated or incorrect.

Bryston amps are known for iron-fisted bass control, but the Esoteric bettered the 6B in this regard. Billy Cobham’s fast-and-furious drum strokes on his Spectrum (24/96 FLAC, Rhino) had better percussive impact through the A-02. The A-02’s superior performance was also evinced in the higher frequencies. When Cobham unleashed his signature snare rolls, the A-02 rendered them with better pop.

Moreover, it was not a shock that, as I explained in my review of the YG Acoustics Kipod II Signature, the A-02 (which was in for review during the tail end of the Kipod sessions) also sounded more refined, detailed, clean, and quiet than the Bryston. As evidenced by Diana Krall’s The Girl in the Other Room (CD, Verve B0003758-82), it also had a rounder, richer, more textured midrange.

Don’t take this as a knock against the Bryston. It held its own in my system, and never sounded bad. That’s actually quite a compliment -- the Kipod II suffers no fools. At the end of the day, however, the A-02 was undoubtedly the better amp, and more at home in a highly resolving and expensive system such as mine. Once you’ve spent the money on everything else, you don’t want to skimp on amplification. If you do, you won’t be hearing everything your system has to offer.


The A-02 has brawn, tough-to-beat sound, museum-quality looks, and Esoteric’s reputation for rock-solid reliability. You don’t typically find all of those qualities in one amplifier. Apparently, Sound Inn agrees -- currently using two A-02s, they’re considering buying five more, so that they’ll have one in each of their seven recording rooms. If your system would benefit from high power and is good enough to reveal what the Esoteric A-02 can do, look no further.

. . . Howard Kneller

Associated Equipment

  • Amplifiers -- Bryston 6B SST2
  • Preamplifiers -- Esoteric C-03
  • Sources/DAC -- Esoteric K-03 CD/SACD player, netbook computer running Windows 7 and JRiver Media Center 17
  • Speakers -- MartinLogan Summit X, YG Acoustics Kipod II Signature
  • Interconnects -- Synergistic Research Element Series
  • Digital cable -- Synergistic Research Tricon USB
  • Speaker cables -- Synergistic Research Element Copper-Tungsten-Silver
  • Power cords -- Synergistic Research Tesla Hologram A (amplifier) and D SE (source), Precision AC (speakers, Powercell 4 power conditioner), Precision AC SE (Powercell 10SE power conditioner), T2 SE (preamplifier)
  • Power conditioners and distribution -- Synergistic Research Powercell 10SE Mk.II daisy-chained to Powercell 4 (digital), Synergistic Research QLS 6, and 9 line strips
  • Isolation devices -- Bright Star Audio IsoRock reference platform, Synergistic Research MIGS, Mapleshade Heavy Hats, DIY amp stands
  • Misc. -- Synergistic Research Galileo Universal interconnect and speaker-cable cells, Synergistic Research Galileo MPCs on all signal cables and power cords

Esoteric A-02 Stereo Amplifier
Price: $17,600 USD.
Warranty: Two years parts and labor.

Esoteric Division
TEAC America, Inc.
7733 Telegraph Road
Montebello, CA 90640
Phone: (323) 726-0303
Fax: (323) 727-7650