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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: 27" iMac with 3.4GHz quad-core Intel Core i7, 16GB 1.333MHz RAM, 2TB hard disc, 256GB SSD drive, ADM Radeon HD 6970M with 2GB of GDDR5 memory, PureMusic 1.86 in hybrid memory play with pre-allocated RAM and AIFF files up to 24/192; Audirvana 1.3.9.9 in direct/integer mode, April Music Eximus DP1, Esoteric/APL Hifi UX1/NWO-M w. Audiophilleo 2
Preamp/Integrated: ModWright LS-100 with Psvane 6SN7, Esoteric C-03, Bent Audio Tap-X, TruLife Audio Athena
Amplifiers: First Watt SIT1, FirstWatt SIT2, ModWright KWA-100 SE, Bakoon AMP-11R, AURALiC Merak [on review], Acoustic Imagery Atsah [on review]
Speakers: Aries Cerat Gladius, Boenicke Audio B10, Voxativ Ampeggio, AudioSolutions Rhapsody 200 [on review]
Cables: Complete loom of Zu Audio Event, KingRex uArt USB cable with Bakoon BPS-02 battery supply
Stands: Artesania Esoteric double-wide 3-tier with TT glass shelf, Rajasthani hard-wood amp rack
Powerline conditioning: GigaWatt PF2 on amp, GigaWatt PC3 SE Evo on front-end components]
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: $6.500


700 is 200 more than 500. As a presumption on how the Stello Ai700 might loom over its Ai500 stable mate, we'd expect - well, 40% more. But the 200 less integrated from Simon Lee's Stello range already is sock(et)ed out to the max. It even has digital inputs including 24/192 USB based on the XMOS-powered asynchronous Stello U3.  
Stello Ai500


Ai500 open
  It arrives with iPod charger port, balanced inputs, fixed and variable outputs. It sports an FMJ remote, top-notch build quality and snazzy designer cosmetics from Korea's Metal Sound Design. And it delivers truly excellent 150/300wpc power into 8/4Ω that takes to demanding Magnepan divas like the devil does to the devious. Numerous trade show commentary have said so. In short the Ai500 is quite the bomb. The newcomer's more couldn't apply to features, only to sound.


Even that promised to be a tall order. The smaller machine's prior showings had elicited very loud applause in this and other publications. Realistically speaking, just how much more performance was possible to demonstrably eclipse the Ai500 for twice the coin? How much sexier a chassis was possible to cater to equally important pride of ownership without overkill metal work of silly bank-vault ambitions? How to accomplish this with sufficient breathing room left for the Eximus range to stretch its legs and justify its even higher stature?


The two bridged ICEpower boards
are clearly visible on either side of the toroid
  When I learnt that the 700 is ICE'd—the 500 is parallel p/p class AB—I did wonder. The Eximus S1 also runs on B&O power modules. And in the Korean catalogue Eximus tops Stello. Delivering perfectly respectable highly civilized power on the warm side of the fence, the class D S1 hadn't completely moved me. I thus expected the Ai700 to face all manner of presumptions. But Simon Lee proved undeterred: "The Ai700 is far superior to the Ai500. That's not because class D trumps AB. It's because the Ai700's input buffer stage  is around 4 times more advanced than what was in the S1 (which in due time will undergo an upgrade). Prior to their ASX250 series I did not really like any current class D including earlier B&O. Even so I don't snob operational classes of output circuits. Whatever makes superior sound wins. Now I am working hard on finalizing the Ai700 chassis."

Ai700 prototype with Aurender source and Wilson Sasha speakers

Class D keeps making inroads. The latest Ncore announcements had Jeff Rowland on board. PS Audio was working on a UcD 400-based platform. Power supply would either be linear or switch-mode. During an early R&D stage Paul McGowan shared that the SMPS seemed to be winning. Like the Colorado team AURALiC from Hong Kong too had opted for modified Hypex over Ncore boards to control their final retail price. The Merak monos run on 500-watt linear power supplies with custom balanced input buffers and Lundahl input transformers. Past ICEpower-based Jeff Rowland models had fancied input transformers as well. Wyred's EJ Sarmento is known for custom-tailoring fully balanced input buffers to specific B&O modules. Bel Canto Design champions virtual battery supplies. There's consensus then on how the input circuits which must precede various stock class D modules impact final sonics. It's in fact their core distinction if we subtract enclosure bling and brand status.

Yet the biggest perception hurdle remains. For most commercial class D that's simply not being designed here. As retail prices increase, said hurdle grows in height. It's a fact Ncore/Hypex's Bruno Putzeys exploits very strategically with his new Mola-Mola brand. Unlike Bel Canto, Wyred4Sound, Peachtree Audio, April Music and many others, Putzeys can rightfully claim designed here by 100%. That affects perception of his stiff 10K tag for a pair of high-power class D amps. Such a sticker now becomes equally viable as an equivalent one for luxury linear amps. While we're still on perception, we must grant Simon Lee a few more hurdles. His Eximus brand is the Lexus equivalent of Stello's Toyota. Doesn't the "four times more advanced" input circuit of the Stello Ai700 pose a serious threat to the existing Eximus S1?

Quoting from my review of it, "... sharing its handsome 208 x 62 x 291mm WxHxD chassis with the previously reviewed Eximus DP1, the 2.9kg S1 is a bridgeable amp. In makes 125 watts into 8Ω in stereo and 500 watts in mono mode. It is based on B&O's 250ASX2 ICEpower module. Simon finds that its "unique circuit design and state-of-the-art semiconductor technology outclass the performance parameter of class A/B amplifier designs". Compared to B&O's top-power 1000ASP board, this module has half the distortion, 4dB more dynamic range and 7% higher operational efficiency. It offers dynamic range of 112/121dB in stereo/bridge mode and TDH+N of 0.008 and 0.003%. Consider how the BTL measurements are superior to single-ended..."