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Taking a page from Apple's evergreen playbook, STU arrives packed in fully engineered boxing with proper quick-start documentation in various languages. This stresses right off that its sender is a mega corporation. Few others can or bother to create such a slick presentation for a $399 product. Obviously knuckle-wrapping the slim box once unpacked sounds tinny; the stand is molded plastic not machined alu; and the small SMPS brick ends in a figure-8 not 3-pin IEC to only take the included power cord. Just sayin' to keep it real.


Even so the front, top and sides play it properly ff. Here that's not for fortissimo but fastener free. In fact not knowing how to safely pop this apparent snap-on cover without marring things, I refrained without first emailing Raja. He sent this how-to PDF. Undo six belly screws, use finger nails. No rocket science. But do push the cover away from the front first to disengage the fascia latches. Or your nails will break.


Back on the outside, the two volume controls have nicely snug smooth mechanical action far from flimsy. Ditto for the sturdy chassis-mount RCA outputs around back and the toggle trigger for headphone gain. This is a nicely appointed lightweight deck in understated chic.


First impressions fronted by Astell&Kern's AK100—modified by Red Wine Audio and leashed up with AudioQuest's best glass-fiber optical link called Diamond—were of a thick and ambiguous i.e. chunky but opaque sound over translucent teased-out resolution. Like a deliberate counter voicing to more nervous pseudo-rez or pale washed-out kit. Think iPod headphone output. Think straight iTunes from non-optimized laptops without dedicated player software. But coppers on the affordable hifi beat used to patrolling the posh turf don't know the going sonic rates in the barrio. What to expect, realistically?

I had AMI Musik's DS5 on hand. But in these strata $599 are light years removed from $399. Companies undergo pains to shave off a dime here, a penny there on the BOM or bill of materials. Such efforts add up to $50 or $100 advantages on the retail floor. Those make the difference between a sale or not. Yet comparing apples and oranges which to a high-roller look the same is what we who write about this stuff often do. We don't carry inventories of all component categories at all price points to do any better.

Back on track. If you're twitchy fingered and strong nailed, this list of op-amp rolling options gets you going. Pull the LM49720 I/V conversion and LM4562 low-pass filter chips. Here's what we're told to expect:


I/V rolling with stock LPF in place: LM49720 stock– well balanced, clean, airy and open but slightly to the warm side.
LM49720 ‘metal can’– almost identical to stock but just a tad fuller in body.
OPA2604 – denser, not as airy and open as stock.
OPA2209 – bass is a little lean with good height.
OP270 – Also dense but a little better soundstage than OPA2604.
OP275 – Leaner and brighter than stock, almost grainy. Good soundstage.
AD8066 – Even brighter than OP275 but without the graininess. Slightly flat of soundstage but with good width.
OPA2227 – Forward, full and bright, slightly grainy.
OPA2134 – More midrange-centric, lacks in soundstage.
MUSES01 – Similar to stock but with better dynamics and a more impressive soundstage.
MUSES920 – full and forward like a smoother OPA2227.
The blue bits here are four out of six jumpers.
LPF rolling with stock I/V in place: LM4562 stock – well balanced, clean, airy and open but slightly to the warm side.
LM49720 ‘metal can’ – similar to stock, slightly less dense and more open in the mids.
OPA2604 – thick, slow and grainy.
OPA2209 – Full, similar to OPA2604 but without being overly thick and slow.
OP270 – Lean, slightly lacking in bass, slightly bright.
OP275 – Well balanced though the soundstage isn’t great.
AD8066 – Very airy and open with a great soundstage but a little bright.
AD8620 – Like a tuned-down version of AD8066 with better body and a smoother presentation.
OPA2227 – warm and slightly dull but still sparkly on the top.
OPA2134 – similar to OPA2227, more midrange-centric and not as sparkly.
MUSES01 – Similar to stock but with slightly better dynamics and soundstage.
MUSES8920 – somewhere between OPA2227 and OPA2134.


For review purposes I stuck with stock and left the default jumpers for no DC servo and no volume control bypass. The DC servo avoids turn-on transients for headphones. I'd say don't wear 'em until STU is live and leave the default be.