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To test raw drive and grunt, I leashed up the 85dB 4-ohm Mark & Daniel Maximus Monitor with optional >3kHz ambient omni tweeter. Because this speaker sports a forced bass alignment and high Xmas mid/woofer, it thrives on current and damping factor, i.e. low amplifier output impedance. The A-100 had zero issues with SPLs, bass extension or treble finesse even with the OmniHarmonizer tweeters at full output (rather than being attenuated via the secondary binding posts). Hearing this affordable, tube-hating monster speaker with valves was quite the treat. Mind you, its hate of glowing bits is purely due to the load, efficiency and challenging bass alignment it presents to them. And of course every rule has its exceptions. At the Maximus Monitors' $3K price however, chances of finding a price-matched valve amp that will drive 'em to anywhere near their full potential are pretty damn slim. As a low-power valve fancier, I don't own high-power tube amps yet. Hence I was enjoying the spectacle of seeing my gnarly Maximus warriors stretch their legs on an upscale thermionic diet for a change.


As a dedicated bi-wire speaker, the EU/CE-approved, slotted shrouded posts of the A-100 won't accommodate the stacked spades my cable assortment and Maximii call for. You'd need a spade/banana combo which I don't have. Single-wire it was then. Fine. Given the A-100's luxury tag though, some will wish for 'stackable' terminals. I'd not blame them.


The A-100 clearly uses relatively low feedback to run with high output impedance. Here it parlayed as unduly bloomy, somewhat excessive low bass with shocking extension (that's the speaker) but sub optimal control (that's the amp but admittedly, this speaker asks for a very firm hand to be its best). The 8-ohm tap fared audibly worse, suggesting the amp struggled a bit. The 4-ohm feed was better but -- believe it from this 6.5" two-way! -- still produced too much low- and midbass amplitude with embedded ringiness as though the amp wasn't quick enough on the brakes. This was deliberate amp cruelty of course. Considering Esoteric's concept of 45-watt ultra-refined push/pull tube amp, I was impressed how well it worked in general. Considering the price tag however, I wasn't. For that, I want it all. This simply reminds us. Regardless of price, mismatching an amp and its load won't ever jump the fence to run completely free and off the leash. It's not a matter of throwing money at the problem. It's a matter of solving the problem with a more complementary match in the first place. That'll give better performance. And could save serious coin. Hifi 101. Get thee the proper tool for the job at hand.



However, this mismatch proved instructive not just by confirming how not to play the game. The speaker's dual air-motion transformers (the big curved AMT from 800Hz on up, the small upfiring auxiliary AMT above 3000Hz capped with a dispersion lens) have a far higher upper mid/treble power response than standard cones 'n' domes. Hence amplifier contributions of hash, sizzle, particle dirt and such have nowhere to hide. Your nerves will frazzle first.


It's here that our mismatch proved exceedingly copasetic. Plainly put, the A-100 is a weltmeister in the treble, a true redeemer of SET-reared expectations. It's mere presumption on my part but if the amp's sophisticated auto-bias system operates as accurate as claimed, this treble suavity would be the logical upside of that technological low down. That and sufficient bandwidth to avoid audible HF phase shift. Besides superior articulation in general, single-ended amplifiers tend to have more refined trebles, most likely because they need not match output devices or their bias. Nor is there phase splitting and subsequent recombining of phase halves to contend with. Here high frequencies are prime proving grounds.


When a push/pull amp makes treble that for all intents and purposes suggests single-ended operation, you can bet that its output devices are stringently matched; that its bias protocol is tight and ultra specific; and that bandwidth extends at least two octaves above your hearing cutoff. You'd likely also be correct to assume low feedback. Most the time, high feedback dries up the upper bands to diminish or eliminate that trailing elasticity and translucence we love from SETs.


Based on the evidence thus far, should one call the A-100 a powerful single-ended valve amp in disguise? To check how close the Esoteric might come to such an unusual promise, I turned to my DeVore Fidelity Nines. In my review of Esoteric's Magnesium floorstanders -- which were used at HighEnd 2008 in Munich on the A-100 -- I stated how the 91dB DeVores are very similar in basic driver complement. The biggest differences are the Nines' side-firing woofer and non-metallic diaphragms. To get as close as possible to Ohmachi-San's personal hardware setup, the Nines from my resident speaker harem were simply perfect in more ways than that.


Now the A-100 was fully in its element. The treble ravishment translated intact as did bass depth. Bass boominess and LF distortion were history. The latter tends to translate as increased amplitude, dirtiness, bloatedness and a lack of separated accuracy. Especially on its 8-ohm feed, the A-100 on the M&Ds seemed quite high in bass distortion as I reached the outer limits of its power band. Again, none of this was an issue with the DeVores. They presented an apparently ideal load, including no magnification of operational noise (on my high-efficiency speakers, the A-100 exhibited mild tweeter hiss and midrange hum with the ear on the drivers).


Seeing the A-100 acting like a single-ended amp in the treble and with high-Z bass effects to mandate friendly bass systems also like most SETs, how about the vocal band? Many triode fanciers will pass over the KT88 as a 'commoner's pentode'. Brazilian amp designer Eduardo de Lima of Audiopax hasn't. His celebrated Model 88 with series-connected single-ended operation and truly kinky bias proved the hidden potential for true greatness in this tube. John Potis, formerly on staff, refers to the KT88 as a "transistory" valve due to its innate linearity and refusal to play overt voicing tricks (no EL34 warmth, no 300B midrange emphasis). If we mix together such observations and precedents, where does that place Esoteric's A-100?


It's surprisingly close to Trafomatic Audio's Experience Reference PSE 300B monos when those are fitted with EAT 300Bs and EML 5U4Gs. Those interstage transformer-coupled parallel single-ended Serbian monos with truly gargantuan double C-core output iron likewise refuse to play the 'deep triode' games which suit Jazz ballads but little else. Coming from a very modern SET with higher apparent damping and less 'fluffiness' than common, the A-100 indeed gets very close. Whether it's the KT88s or remnants of push/pull operation, it does not to quite carve out vocals from surrounding space in that peculiar halo of heightened holography which direct-heated power triodes zoom in on in parts of the soundstage and which the Western Electric 300Bs do very well.


Yet the Esoteric retains a very high percentage of this action to really and truly go beyond the usual push-pulliness. Stage width is squarely in the p/p domain, i.e. well beyond the speakers and deep into the corners. Back to triodes again, the sound also distributes well into the room. Despite how it reads, that's no function of speaker dispersion patterns in this case. A simple amp swap on the same speaker can affect whether the sound will seem to 'sit' behind the speaker or spread out forward toward the listener (not at all the same as staging in front of the baffle-to-baffle line either).


Even though their combined cone surface wouldn't suggest it to some, the Nines in a 14' x 20' room are capable of excellent, non-lumpy deep bass with excellent pitch definition. The A-100 maximized this asset to give a very different rendering than over the M&Ds - except for plumbing the very same counter-intuitive depths. What was bloomy, overdone, murky and resonant before now was properly damped, cleanly separated and impactful without 'dust clouds'. In short, this was very good bass regardless of circuit class or output type. Well recorded vocals with ambitious drum kits -- Lisa Gerrard, Eleni Tsaligopoulou, Glykeria, Siam James, Angelique Ionatas to chart a mostly Grecian course -- were a true delight, on top for cymbals and brushes, down low for big drums, synth pedals and assorted bass effects.


Most importantly from the listener pleasure seat: The DeVore Nines, to my ear, are very fussy about amps. They will always sound clean, clear, composed and unruffled. They are an easy friendly load to make lesser results usually the amp's fault. However, their cleanliness and neutrality can default into something a mite boring when you come from high-efficiency designs big on tone and dynamics as is my habit. It's thus always of particular personal interest to me how amps fare on the DeVores. The last one to gain High Nines applause -- utterly unexpectedly I might add -- was the diminutive NuForce Icon. The earlier referenced Trafomatic Experience Reference did fine but sounded a lot more magical on the Zu Presence or Rethm Saadhana. But the A-100 hit the Nines' G-spot. I don't know what makes it so. I haven't discovered any predictable pattern in the amps which kowtow to their special desires and those which don't.


I translate the A-100's excellent showing on the DeVores as making great tone density to just the right degree, i.e. without introducing any ponderousness or thickening. You can diminish the volume and still explore all the very fine stuff without finding it obliterated by clumping things together to get amorphosized. This twin action of low-level separation against great tone density is a prime achievement since it must walk a very fine line. While the treble is thus mostly single-ended, the midrange and bass are an even-handed mix of SE and PP. Detail retrieval -- ambiance, soundstage depth, clarity on tiny rustles, rainsticks and other noises -- meanwhile suggests lower 2nd-order distortion than would be typical for single-ended. It could suggests gobs of distortion-cancelling feedback. Which we know from the low damping factor not to be the case. So we simply credit good engineering and excellent ears leading the engineers.


From this hand of attributes, you will appreciate that Ohmachi-San's reference amplifier is not your typical KT88 p/p trump card. It sounds mostly -- but not completely -- like a very good modern linear single-ended triode amp with better bass. The same limitations of ultimate drive into low impedances and frequencies apply just as they do with bona fide SETs though the higher power available here broadens the scope of applicable speakers significantly. The focus of Esoteric's newest and most ambitious amplifier is thus squarely on sophistication and refinement, not muscle and load invariance. The target audience is the resourceful 45-watt triode aficionado who wants precision auto bias but not designer triodes; superlative built quality and noise performance; linear even-keeled magic, not voicing tricks; superior bass; and guaranteed sonics from currently produced glass which won't cost fortunes to replace.