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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: Esoteric UX-1, Yamamoto YDA-01, Ancient Audio Lektor Prime, Raysonic Audio CD228 [on review]
Preamp/Integrated: Esoteric C-03 (transistor), ModWright DM 36.5 (valves), April Music Stello Ai500 [on review]
Amplifier: Yamamoto A-09S, FirstWAtt F5, ModWright KWA-150, Octave MRE-130 monos, FirstWatt J2 [on review]
Speakers: ASI Tango R, Zu Essence
Headphones: Audio-Technica WHT-1000, Beyer Dynamic DT880, AKG K-1000, Sennheiser HD800
Headphone amplifier: Yamamoto HA-02, Woo Audio Model 5 with EAT 300Bs, KingRex HeadQuarters [on review]
Cables: Complete loom of ASI Liveline
Stands: ASI HeartSong [on review], Ikea Molger with butcher-block platforms
Powerline conditioning: 2 x Walker Audio Velocitor S
Sundry accessories: Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; extensive use of Acoustic System Resonators, noise filters and phase inverters, Advanced Acoustics Orbis Wall & Corner units
Room size: The sound platform is 3 x 4.5m with a 2-story slanted ceiling above; four steps below continue into an 8m long combined open kitchen, dining room and office, an area which widens to 5.2m with a 2.8m ceiling; the sound platform space is open to a 2nd story landing and, via spiral stair case, to a 3rd-floor studio; concrete floor, concrete and brick walls from a converted barn with no parallel walls nor perfect right angles; short-wall setup with speaker backs facing the 8-meter expanse and 2nd-story landing.
Review Component Retail : $349

Let's play checkers. Got upscale DAC without USB input? Check. Got CD player or transport with RCA digital input but no USB? Check. Want to listen to computer music files? Check.


Actually, it's checkered mate. Against you. For such scenarios, April Music has created the Stello U2, a self-powered USB-in, S/PDIF-out converter. For all of $349, tiny at 10 x 2.7 x 5.6cm WxHxD and light at 270 grams, it's you now who declares victory against your frustrated desires. There's also a 5-pin DIN I²S output but your current kit likely won't sport the necessary counter part.

The U2 is far from the first of its kind. Bel Canto Design for example attracted attention with their USB Link. That retails for $495, i.e. $150 more. The Stello's monolithic extrusion is classier, the Bel Canto adds a Stereovox XV2 BNC/BNC cable with RCA adaptor. Whether you call it a wash will depend. There are US vs. Korean allegiances, present ownership of a good digital cable (or not) and the state of your purse.


If PC audio at present is still transitional, then the U2 is a twice transitional product. It aims to fill the cracks, bridge the chasm until things settle down. The friendly sticker and bare-boned simplicity are just right then.

The U2 sternly resists code breaking. Its circuit board is soldered to the stout RCA. Without de-soldering the connector from the board, you can't lift out the PCB to flip it over and study the parts. Chances are high you'd find the ubiquitous BB PCM 2704 digital receiver. But April Music promises more by way of noise filtering and galvanic isolation. There's also a proper temperature-controlled crystal oscillator clock.


Here's one way of looking at this device. It's common knowledge by now that unless you run a true trophy Redbook transport, a far cheaper computer drive built into a MacBook or Windows machine will—perhaps by virtue of magnetic rather than optical playback—perform better. If the U2's USB-to-S/PDIF conversion were inferior to what's inside a dedicated super USB DAC of Wavelength Audio caliber, one might still come out even (or ahead) when comparing a solid conventional CD player to PC + U2 + converter of choice.


Folks like myself who enjoy a top-class Redbook transport and premium DAC already are unwilling to trade them. If we want to add USB without buying a second full DAC, the U2 could be the ticket. Unless our present DAC sports multiple S-/PDIF RCA inputs, we'll just have to swap wires. Clearly, the U2 is a niche product within the small niche of audiophiles who even run with separate D/A converters. For those presently not be-dac'd, the $299 High Definition Technologies Streamer + should be the altogether better choice. For less money than Stello asks, it combines U2 functionality with a full D/A converter to output analog signal. It does not require a separate converter as does the Stello. As I see it then, the Stello is primarily meant for audiophiles who already possess a high-quality DAC—or CDP with digital input—but want to add USB without a grand outlay of cash. Sometimes simple and cheap is the solution. This could be thrice true in a product category as in flux as digital audio continues to be.
 
The U2 requires no special drivers and shakes hands with PCs automatically. Depending on what software and operating system you run, you may have to create the initial pathway in a config window by selecting TE7020 Audio w/SPDIF, the computer name of the U2. Signal lock is confirmed by a small red LED on the front and displacement by heavy cabling is prevented with a sticky pad glued to the full length of the playing-card-sized belly. How best to test this machine? Still having Stello's Ai500 integrated amplifier on hand which offers USB and S/PDIF digital inputs, the answer was easy. I'd compare my MacBook Pro into the U2 into the coaxial digital input vs. going directly into the USB input. If I couldn't tell the difference, we'd know that the U2 packs the same quality conversion in its little extrusion as April Music's most ambitious yet—sold in the West—machine does inside its big oval box. The results were unexpected.