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The coincident presence of the Ai700, Acoustic Imagery Atsah and AURALiC Merak amps confirmed it. D for prez has become a legitimate bumper sticker even for the Lincoln Town Car driver. Be it Bruno Putzeys' Ncore 1200 modules with SMPS in the Atsah monos; modified Putzeys UcD 400 modules plus Lundahl input transformers, balanced class A drivers and linear power supplies in the Meraks; or Simon Lee's latest-gen ICEpower with mondo class A balanced drivers and SMPS - this sector has made surprising advances. As Aussie contributor John Darko put it reporting directly from RMAF 2012: "The finest-sounding room of the day was that of South Korea’s April Music. Fronted by the Eximus DP1 running balanced out into their new Stello Ai700, this new model is essentially two of the shoebox Eximus S1 amplifiers distilled into one unit but fuelled by a bigger badder power supply. April Music were using a Macbook with Amarra as transport." Replace MacBook with iMac and Amarra with Audirvana and John was talking about my system.
AudioSolutions' Rhapsody 200 flagship speakers with Atsah/Ai700 and Eximus DP1 in balanced drive
Where Simon's S1 had repented* too much for my tastes—it turned early class D's bright relentless glass-shard detail on its head—the Ai700 retreats a bit from that darkness. It moves back towards the light without relinquishing any gains the former's descent into the materialism of mass had already made.
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* In the New Testament, repentance is a translation of the Greek μετάνοια or metanoia. This compound word denotes 'to think differently after' or simply 'a change of consciousness'.
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On the Lithuanian 5-driver 3-way towers whose review described a legacy Sonus faber sound with higher resolution and a far more American than European bass balance, the slightly leaner more lucid Ncore monos were the ideal mates. Very linear ultra-low Z-out (1.3mΩ up to 17kHz, 3mΩ above) had perfectly damped their deliberately lower Qms ported bass alignment. The Ai700's overall warmer character and stronger upper bass combined into the same load for a somewhat elephantine low end. This also thickened and thus slightly obscured the twinned SB Acoustics midranges.
With Eximus DP1 set to fixed output at 3:00
On my customary Aries Cerat Gladius zebras meanwhile whose sealed 12" Fostex woofer loads into far smaller cubic volume for not merely less extension but less LF amplitude and an overall lighter quicker demeanor topped off by a Serbian Raal ribbon, the Ai700 created the more developed bass. In general it also hung a bit more fleshiness on the Gladius frame. If I wanted a tad more incisiveness or quicksilver injection, I'd replace the Eximus DP1 with the fully balanced $899 Muses Edition Asus Xonar Essence One. That's a bit more lit up, angular and lean than the Korean converter.

While I ultimately think that Ncore's tech is the more advanced—Dutch eat Danish is how that review puts it—there's early consensus. Formal production rather than DIY demands at least $9.000/pr. That's what both Acoustic Imagery and Merrill Audio want. Bruno's own Mola-Mola is $10K. Though Ncore 1200 prefers no preamps for balanced DAC-direct drive (analog volume is a prerequisite), many converters lack remote. If you're a playlist or shuffle mode hound, small track-to-track volume trims are de rigueur. Now remote is obligatory. At $6.500, the Ai700 not only obliges, it subtracts amp-drive duties from the DAC.


The latest-gen ICEpower modules—I've now experienced them in Wyred4Sound, Peachtree Audio and two April Music implementations—are warmer, darker, softer and more organic than diehard street rep knows is possible for the breed. While they retain that character vis-à-vis Ncore which is more transparent and sorted, what all of these current proponents of switching output stages (modified uCd included) share is dense detail and detail density. Their soundstage is chock-a-block with musical detail. Unlike before though, this detail isn't edge-rimmed, bright or hyper focused. It's undeniably there and is so en masse. It now simply coexists with material gravitas. Call it the heaviness of substance. It's no longer a sharp-toothed piranha swarm in a feeding frenzy. It's a benign school of bigger fish passing by stately.

As playback levels increase, this heaviness increases in lockstep. And because detail capture is immense, high volumes create a particular intensity that gets nearly oppressive by how much virtual space it occupies. This is different from my low-power class A FirstWatt amps. Those are more illuminated from within, more aerated, more translucent. They have the more effervescent top end. They are lithe-ankled ballerinas, not stout farm girls. Their damping factors are lower too. Perhaps as we ascend in frequency, less damping means more elasticity and liberty to ring out.


Where an SMPS done right seems to enjoy an unfair advantage is noise. The absence of bulky power transformers can generate S/N ratios of 120dB or better. For power amps! Let that sink in. That's on par with or better than top-resolution DACs. Now compare premium valve preamps. They might be proud to hit 94dB. Forget tube power amps which barely stretch to 85dB. Remove those bottlenecks and you finally hear what our supposedly low-rent 16bit/44.1kHz digital really packs. Ear on tweeter, the 500wpc Ai700 might as well be DOA. There's not even the faintest breathing. Dead as a rusty door nail. If you hear anything, it'll be down to your converter or player. Whatever creaky ailments of noise they suffer simply gets amplified. That certainly wouldn't fault the amp.

April Music's Stello Ai700 strikes me as the perfect antidote to the prototypical Teutonic sound embodied by repeat Burmester trade show demos I've heard. This integrated leaves the detail untouched but obliterates its relentless needling. Ceramic turned paper. Admittedly when mated to already lush dark and chewy speakers, the textural results could get a bit cloying just as they would with certain valve amps. Think peanut butter and chocolate. Bass-heavy speakers designed for US-style sheet-rock construction where LF is louder outside than inside the room will plump up further. The Ai700 is very potent in the upper bass. Anaemic systems thus get a blood infusion. Though it's popular to think otherwise, this stereo integrated exceeds the monaural Eximus brethren. Those really become Stello, the Ai700 Eximus. That's because the latter captures more light where the S1 had gone a bit too dark.

Quick calculator math nets a pair of improved S1 plus one remote-controlled fully balanced preamp. The former two burn up $5.000 of today's sticker. That leaves $1.500 for preamp and wand. In this context Stello clearly equals very good value. The rude equalizer becomes the Grand Integrated from Peachtree Audio. It goes for $2.000 less, runs the very same power modules, then adds a very good 24/192 USB 2.0 DAC and wraps it up with a headphone socket. Simon Lee's B&O implementation might be superior but the Peachtree had already been returned to answer that.
Ai700 at RMAF 2012 with Mårten Design ceramic-driver speakers
  Closing the chapter on class D, Burson Audio for their new class AB Timekeeper amp state that "class D and class T chips were created for the car audio and subsequently the mobile phone industry where power efficiency, size and budget are the driving design parameters to render audio performance secondary." True. But yesterday's news. Opening the chapter on class D, the Stello Ai700 shows how power efficiency and upscale sonics no longer have to be mutually exclusive by design. If you want a meaty very powerful push/pull type sound that's super friendly, accessible, zero maintenance, dead quiet, casually detailed—i.e. very but not pin-point resolved—and integrated to reduce box and cable clutter whilst being built exceptionally well... well, this latest April Music machine really has it all!
April Music website