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The Ai500 in the big system: Preceded by Esoteric's big UX-1 universal machine as transport feeding Yamamoto's YDA-01B converter via Stealth Audio Varidig and followed by Franck Tchang's ASI Tango R speakers via LiveLine cables, April Music's currently biggest baddest amplifier slotted between the Nelson Pass F5 and Dan Wright KWA-150. In output power, it equals the the ModWright, in price the FirstWatt


On the warmth/detail meter, the Ai500 took center stage. The F5 was the most resolved of the three, the KWA-150 the warmest. Compared to my Yamamoto A-09S 300B SET, none of these equal the EML 300B-XLS for dimensional sculpting and tone saturation. Some of this could be injected into the Ai500 with Yamamoto's new B-suffix DAC. That retains the digital section of my all-transistor YDA-01 but goes Western Electric 408A in the output buffer. Still, a truly saturated album like the bombshell 21 Strings, the best of all Al-Andalus Ensemble outings to date, still holds more shades of tonal half shadows in reserve than any of these transistors can completely recreate.


Very appealing then, the Ai500 resisted the urge to unduly highlight the potent metallic attacks of Tarik Banzi's oud. Clearly this is not an outright bluish solid-state amp that's all transients without believable follow-up. This is where the earlier referenced bass power steps in. It lends the sound a downward weightiness. This doesn't exactly equal tubes in textural density or half-light darkness but offers a related version that's very grounded - more so than the FirstWatt for sure while being more fleet-footed than the big ModWright whose impact factor of the three is biggest.



In terms of bass amplitude, the 300B SET on my speakers actually gives up nothing to the FirstWatt but does lose in feathery articulation at low volumes and crunch at higher SPLs. Both transistor muscle amps introduce more amplitude way down low and particularly during violent outbursts, the dust settles quicker from better damping. This improves timbre definition in the low registers to more easily recognize what stirs there.


On Debashish Bhattacharya's new O Shakuntala! [Riverboat 1053], the decays of his expertly pitch-bending 22-string Chaturangui Indian slide guitar with sympathetic registers are necessarily shorter lived than those of a surbahar's far lengthier strings. It's thus vital that an amp not foreshorten those micro fades. The Ai500 did very well and was beat only by the F5 whose possibly even lower noise floor and more lock-jaw tracking of hyper detail has no equal in my present stable.


The Pass amp's more lit-up treble and deeper insight into upper harmonics also helped a bit more on Ljiljana's Buttler's Frozen Roses [Snail Records 66011], a sad case of a once famous artist whose voice is so irreparably damaged as to have lost all legitimacy for issuing yet another recording. With the first release worthwhile, the third is purely gratuitous and the Ai500 produced no reason to alter my opinion. It'd take some serious enhancements of the valve kind to assist this matter. Not here. Abed Azrié's Leonard Cohen pipes meanwhile really cottoned to the Ai500's powerful lower registers on Mystic while Anna-Marie Jopek's occasionally wispy vocals on the Pat Metheny collaboration Upojenie filled out nicely and the Meth man's soaring solos rose effortlessly above an unusually broad stage.


The Ai500 successfully avoided the tinkles, i.e. highly metallic yet overdamped piano which completely subtracts the sound board from the equation and solely concentrates on the attack. Jacques Loussier's superbly mastered 50th Anniversary [Telarc] loved the Korean and its upright bassist had wonderful bloom without the looseness of triodes nor the dryness of certain muscle amps. The deliberate hoarseness in Diego el Cigala's vocal peaks on Dos Lágrimas burned a bit less brightly and the energy of Dhafer Youssef's top-most falsetto on Glow diminished a tad. This amp's tonal center is shifted slightly below middle C.


My room's lack of rear wall generates spectacular depth regardless of speakers or amps. It's primarily width, the reaching behind and around the speakers into the outer corners where I hear differences. The Ai500 was particularly adept at this like a breast stroke swimmer stretching his arms as far as possible before pulling back. Whenever the recording allowed, the sense of soundstage breadth was quite spectacular.


Conclusion Ai500: Free of operational quirks save for somewhat narrow infrared acceptance but like most performance hifi appreciative of 24/7 conditioning over the first two weeks, then 30-minute warm-up cycles to let the output devices reach thermal stability from standby, April Music's Ai500 is a very impressive piece of industrial design. It also flaunts top-notch metal finishing prowess. Priced aggressively, the audio performance is fully commensurate with the cosmetics. Without the benefit of Hegel's patented SoundEngine™ feed-forward error correction which on paper at least makes their H100 integrated the more hi-tech, the Stello's more conventional class AB implementation equals it in sound quality. It simply goes for a somewhat fuller warmer reading with more serious bass than the dead neutral €2,600 Norwegian. It then adds a superior USB DAC, a comprehensive iPod interface, better cosmetics and more comprehensive features.


On features and appearance, the Korean also trumps the boxy Krell S-300i and Metronome's MT One. Meanwhile the coaxial digital input becomes the cat's meow to upgrade an aging CD player without having to reinvest in a dying category. In short, Bryston, Hegel, Krell, simaudio et al must now account for April Music. The Koreans have raised the bar in this sector on functionality and luxury without shortchanging performance.


The Ai500's combination of power, refinement and features in fact mandate calling it a super integrated. This properly distinguishes it from more old-fashioned efforts like Metronome's which is rather more expensive, does a lot less and offers no more performance in trade. In short, the Stello Ai500 demands special recognition:

CDA500 next.
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