Contemporary multibit DAC implementations are becoming increasingly rare. It’s single bit, delta-sigma silicon that now dominates the D/A conversion space, ushered into popularity by manufacturers eager to save on build cost coin. Multibit (aka R-2R Ladder) DACs utilise a series of resistors to generate the 65536 different voltages required for 16 bit resolution whereas newer, 1-bit tech oversamples a fast-moving single switch to generate those same voltages. Such super-fast MHz switching induces noise which must be then pushed out of the audible range. Multi-bit delta-sigma chips that use two or more of these switches require less quantization noise but they don’t eradicate the noise issue entirely.
A simplistic view might be to see delta-sigma’s arrival in the digital audio decoding space as analogous to the arrival of switching amplifiers in a hitherto Class A/B amplification world. And similar to [the occasional dogma of] Class A/B die-hards before them, there are some seasoned digiphiles who’d swear on their Grandmothers’ lives that multibit (R-2R) conversion is not only better in theory than delta-sigma…but that it sounds better too.
OOP(s). With many R-2R chip models now out of production the continued dominance of delta-sigma designs is all but guaranteed. That race is already won. However, there exist manufacturers on the margins prepared to stand firm behind multibit deployment. I don’t buy into the boolean nature of “R-2R = good, delta-sigma = bad” logic and this review certainly doesn’t run to further a white paper dog fight.
‘Round here, each DAC under consideration rises or falls on its own audible merits. Pragmatism over idealism. There’s a “but”. Unintentionally underscoring the idealists’ diatribe, I’ve never heard an R-2R implementation I didn’t like. Alas, I’ve heard a good number of delta-sigma-based implementations that I just couldn’t warm to: Arcam’s rDAC, Calyx’s Coffee and Cambridge Audio’s DacMagic, each offered emotionally distant, greyed out and ‘canned’ interpretations of superior-sounding rivals. Strike one for the ladder lovers? Not quite. Peruse the recently revised Darko DAC Index and you’ll note plenty of delta-sigma designs riding in the upper divisions.
The 24-bit Burr Brown-branded PCM1704U/PCM1704U-J/1704U-K multibit has been marked as unavailable by Texas Instruments. TI’s PCM1704 datasheet page has the delta-sigma PCM1795 supposedly stepping in to fill what some may consider to be BIG shoes.
Even so, the PCM1704-K remains a popular choice among DAC designers who can get their hands on remaining stock.
This writer’s exposure to entry-level PCM1704-K designs first drifted south into Australia from two key new-world Pacific Rim manufacturers. Units from Audio-gd and Lite have each enjoyed coverage on these pages. Then, later, a local design from Gold Coast-ing Lenehan Audio. In recent times I’ve had more deluxe multibit offerings from Naim and AMR in my crosshairs but at the end of 2013 my attention was diverted away from the UK and toward Italy where the lesser-knowAqua Hifi manufacture their statement, Burr-Brown PCM1704-K-toting La Scala MKII DAC. It sells for a not inconsiderable 4890 Euros (~US$6800).
Srajan Ebaen’s coverage of Aqua’s entry-level La Voce S2 DAC at 6Moons serves as foundation to what follows.
Acoustic Quality = Aqua. Their R&D guy Cristian Anelli sets the scene: “Since 2005 we started to research a different solution from the upsampling / oversampling converters. One of the main factors about La Scala and La Voce different sonic approach is the elimination of digital filtering. We realized that the ‘heart of the sound’ lay not only in eliminating the digital filtering but also in the quality of PCM signal transmission (I2S, etc).”
Fashioned at their Milan HQ, Aqua have quietly folded thrice on old school methodology:
1) The La Scala doesn’t come with the digital board alternatives of its younger sibliing, the La Voce S2. With the La Scala you get Hobson’s choice: 4 chunks (2 per channel) of the aforementioned Burr Brown PCM1704-K.
2) DFD = ‘Direct From Decoder’. That’s Aqua speak for a digital decode that bypasses on-chip filters.
“Our DFD circuitry is purely made out of logic gates. La Scala’s DFD circuitry is more sophisticated than the La Voce’s: a galvanic and magnetic separaton circuit is achieved using high-speed opto-couplers.”, continues Anelli.
3) Tubes: a hybrid ECC81(12AT7)/Mosfet pairing runs output staging that’s Class A and doesn’t draw upon negative feedback.
Anelli again: “What is important for a modern DAC is to avoid obsolescence: Aqua’s philosophy allows all previous customers to replace the conversion modules (and new PCB releases) as easy as possible.”
This design modularity recalls California’s Schiit-stirrers Mike Moffat and Jason Stoddard. No need to dispense with your DAC baby when you only wish to refresh the bath water. Similarly, the La Scala MKII assuages anxiety of inherent obsolescence at buy-time. Snap in new digital and/or USB board as and when Aqua bring them to market. At this kind of sticker price such thinking moves beyond Schiit sensible to near-mandatory; a sentiment echoed by AMR whose recent digital board update to their DP-777 converter can be applied to owners of existing version one units.
What else? Power comes from two E-L core transformers, one each for digital and analogue sections. If op-amps cause you to sniff n sneeze know that current-to-voltage conversion is 100% discrete. As one might rightly expect at this end of the market, both single-ended and balanced outputs are included.
All digital inputs deal up to 24bit/192kHz PCM: 75 Ohm BNC, 75 Ohm coaxial, AES/EBU and USB. Windows users will need to install the USB driver available for download from Aqua’s website but I confirmed plug and play status to be flawless on both a MacMini OS 10.9.2 and a Fedora Linux-driven Antipodes DS music server. Want DSD? Look elsewhere. The i2s (“AQLink”) input is for direct coupling to Aqua’s La Diva CD transport (untested here).
USB reception across the swathe of budget D/A converters can best be described as a mixed bag. USB often sounds diluted when compared directly to the same DAC’s neighbouring S/PDIF feed. I start to expect more from decoders that cause financial spill above $2k so I’m pleased (and relieved!) to report that at the even loftier asking price of five thousand Euros, the La Scala’s XMOS USB input is rock solid. When directly connect to a MacMini via USB the La Scala MKII sounded no weaker than calling on the Resonessence Labs Concero HD to intercede as USB-S/PDIF middle man.
Broader flavours. Although stronger on swing and sweetness, the Italian’s eyes don’t bulge with the wide-eyed technicolour tonality of the AURALiC Vega, which wins out for all-round illumination, resolution and (perceived) neutrality. With their INVICTA Mirus, Resonessence Labs take the AURALiC recipe and stir in elegance, beauty and moisture. The Mirus contrasts the Vega as a little ‘chalky’, something I don’t notice with the AURALiC standing alone. This notion of wetter musical skin is what places the La Scala closer to the Mirus than the Vega.
That said, timing and rhythmic snap put the La Scala genetically closer to Metrum’s Hex. The Italian takes the same propulsive DNA but stretches it across a sonic canvas that’s larger than the Dutchman in all three dimensions, especially depth. It’s a presentation that’s cavernous yet location specific. Spatial cues cruise in on the back of more abundant ambient information than any of the aforelisted rivals. A deeper dig for textural detail leads to a better sense of traction – think grippier bow on gut. This is most noticeable among lower bass notes. When things get musically dense, layer delineation doesn’t crumple; even with less than stellar recordings like Arcade Fire’s “No Cars Go”. The La Scala contrasts the Hex’s vibe as more plain Jane, less engaging – again, not something I hear from the Metrum unit standing alone. This comparison has me wondering about the other D/A converter in Aqua’s range. Could the La Voce S2 (2195 Euros) be a viable, similarly-priced alternative to the Metrum Hex? The La Scala MKII might give those considering AMR’s DP-777 pause for thought.
There’s no doubt that this is the finest sounding DAC to date to grace my life/system/website with its presence. Prior to that it was Resonessence Labs’ INVICTA Mirus (US$4995). Aqua Hifi provide us with proof positive that the return on moving well beyond a $5k spend is very real. VERY REAL. Whilst the La Scala MKII is a decoder capable of stunning performance, it remains prowess that’s presented quietly, sans piety and without Aqua needing to substantiate their modus operandi with daft PR proclamations that things aren’t as good as they used to be, that the good old days are behind us, that modern life is rubbish, that summers aren’t as hot as they were when we were kids, that policemen are getting younger or that your current DAC sounds ‘broken’. That spells twice the triumph.
Further information: Aqua Hifi