Aqua Formula xHD DAC
State of the art NOS R2R ladder DAC with DSD compatibility
Review sample supplied by Aqua
Retail prices in the Netherlands (incl 21% VAT):
Formula xHD: 13.670 euro
Upgrade from Formula to Formula xHD: 1085 euro ex shipping to the factory in Italy
Regular readers know that I still have a preference for multi-bit DACs, especially when they’re built in an R2R ladder, discrete resistor-for-resistor fashion. The EC Design Mosaic was my first encounter with a NOS, filterless DAC using discrete resistors, and it shocked me to find that it did several things better than my then reference Jeff Rowland Aeris DAC.
It was mainly due to my then Apogee Diva speakers’ behavior that I could not stick with the Mosaic DAC and settled on a Wadia 521 instead. The 521 can be seen as the classic Wadia team’s last real DAC, and although not built with single resistors and certainly not NOS or filterless, unlike the brand’s current Delta/Sigma DACs, the 521 is a true multi-bit DAC. All Wadias have very natural timbre but older models can sound a little “wooden”. The 521, however, is the smoothest Wadia I’ve heard. I still don’t know exactly why, but Wadias always sound bold and powerful and the 521 is no exception. Naturally, this also ties in with the output stages, and that is where I found the Mosaic to be lacking: in spite of its better low-level resolution and purer sound showcased so clearly by the Divas, its direct-coupled DAC output simply did not sound powerful enough to really bring these speakers to life.
When Cristian Anelli of Aqua contacted me for reviewing the new Formula xHD DAC, I entertained the thought of moving to dynamic speakers and entirely coincidentally I came across a pristine pair of Wilson Watt/Puppy 8 at the same time that several other speakers, as well as several amplifiers, were over for review, and it was at this time that the Formula xHD DAC was delivered. This made it possible to listen to the DAC in very many different system configurations.
Before I dive into the listening aspect, though, first let me explain some more about the Formula xHD DAC.
Formula
With the Formula xHD DAC, Aqua presents an FPGA-based Pure R2R ladder DAC with no oversampling and no digital filter, but including not one but two very potent output stages, one for the single-ended outputs and one for the balanced outputs. The output stages are built onto 4 separate circuit boards using only discrete components, so transistors, not op-amps, and the balanced outputs are transformer-coupled. This promises not only superb refinement and soundstage layering but also a powerful output.
Optologic is what Aqua calls their DAC system, which uses multi-bit technology as used in their La Voce DAC but with a discrete R2R resistor ladder instead of a Burr-Brown PCM1704 DAC. Further, the Formula DAC has a sign-magnitude converter structure, which requires not two but four 24 bit resistors banks, each one made of very low tolerance discrete resistors. Furthermore, there is Galvanic and Magnetic isolation between the FPGA and the four branches of the R2R ladder converter. According to the manufacturer, “This creates complete isolation of all digital circuitry – including the clock – from the analog section for a pure clean ground plane”. And “It also plays the main role in the differential management of the R2R ladders, achieving perfect symmetry between the counter-phase halves”. The official documentation then concludes: “The result is the highest tonal contrast and naturalness never heard before from digital sources”. Big words, but as would soon turn out during listening, fully justified.
Formula xHD
The Formula DAC has been out for a few years but was recently updated to Formula xHD status. Compared to the Formula DAC it now includes new optimized firmware for the main FPGA and a new hybrid architecture USB board with fully-floating (isolated) USB decoding and clock generation by FPGA with proprietary code. Finally, the upgrade also added full DSD compatibility.
Below are some of the most important features:
- Proprietary hybrid 2-stage XMOS xCore XE216 + FPGA
- Fully-floating (isolated) USB decoding and clock generation by FPGA with proprietary code
- Sample rate in “Bit Perfect” up to 768 kHz PCM and quad-rate DSD (DSD256)
- Latest version of customized XMOS X Core Driver on Windows OS (W7, W10)
- Native X Core Audio on Mac OS (Bit Perfect)
- USB Audio 2.0 operation on Linux (Bit Perfect)
And while I’m in spec-mode anyway, let’s include some more manufacturer-supplied technical info: “The Formula DAC uses no digital filter or any other compensation, relying instead on maniacal attention to each subcircuit. The analog and digital power supplies are executed purely discrete by extensive use of BJT, Mosfet, Jfet and ultra-fast diodes. Passive parts were selected not just for the best sonic result but also for their top quality, longevity, and reliability. With the exception of six superior quality electrolytics, all other caps are Tantalum, solid-polymer OS-CON and double-metalized MJP. The signal path itself is direct-coupled and free of all capacitors. The two output stages (one single-ended, one transformer-coupled balanced) use discrete BJT and JFET with metal-film resistors. All the electronics parts show an ultra-low RF noise”.
Lots of buzz words for sure, and all this indeed reads like very thorough attention to detail and a very carefully built product. But in the end, all the technology in the world means nothing if it does not distill into great sound. Fortunately, after having heard the Formula xHD DAC, I can testify that this DAC is truly magnificent!
Connectivity
As you would expect, the Formula xHD DAC is compatible with virtually all sources. Naturally, the DAC offers all the usual inputs such as SPDIF on RCA (cinch), SPDIF on BNC and AES/EBU as well as USB, but also has a proprietary AQlink input which provides an I2S connection for their own CD transport as well as music servers which use the same standard. Additionally, there is a Modular input which can be opted for during purchase or later, should the connection needs change in the future. The available options for the Modular Input are AES/EBU, RCA, AT&T ST Glass and Optical TOSlink. This modular input is a great feature, which only shows the top of the iceberg in terms of the utterly modular concept that the xHD DAC is.
Inside everything is divided into separate boards which can be swapped if and when the need arises. The change from Formula DAC to Formula xHD has been the perfect example of the advantage of this concept, allowing the DAC to be upgraded by only swapping the USB board. How’s that for future-proofing?
The outputs are available in balanced (transformer-coupled) XLR and (direct coupled) cinch. There is an IR sensor but no supplied remote control. For this, Aqua has an optionally available system remote control, capable of operating the CD transport as well as the DAC.
Above and below: this is the optionally available B-21 remote control. The buttons are well laid out and it operates intuitively. It looks heavier than it is but is very sturdy nevertheless.
While this sure is a very nice remote control, it would have been even better if a standard remote control was included while having this luxury version as an option.
Hi Christiaan, I’m about to change my Bryston BDA-2 with a new dac.
My dilemma is right between Bricasti M1 SE and Aqua Formula xHD.
Who better than You can give me the right advice, having heard them in comparison?
I know they are both excellent dac, but I would like to know, having to keep only one, which is your choice.
If you prefer answer to me in private, I left my e-mail.
Many thanks
Roby
Hi Roby, these two DACs could not be more different, meaning that this is very much a personal matter. What I would choose personally ties in with my preferences and the rest of my system and can change depending for example on which preamp and speakers I use.
Basically: if you want to relax in a luxurious smoothness and a more forgiving sound: go with the Bricasti. If you want superb articulation and the highest resolution and transparency as well as tonal accuracy: go for the Aqua. Technically, and importantly for me as a reviewer, the Aqua is more revealing and so it is better at outlining differences upstream and so is better for assessing Music Servers. It is not only a good reviewer’s tool though, I also find that I prefer it for its more honest sound most of the time, even if it can lay bare deficiencies in the source material. In addition to its more revealing character, it is also more “alive” which lately I find one of the most important aspects of sound. But again: this is very personal. My reasons and taste need not match yours.
Tank You Christiaan,
My system:
Bryston BDP-2 / BCD-1
Convergent SL1 Ultimate MKII
Bryston BDP-26
Bryston 7B sst2 mono
Convergent JL2
PMC BB5i Passive (A loudspeakers)
Rogers LS 5/9 – LS 3/5a (B, C loudspeakers)
Which one do you see best in this system?
Thank You again
Sorry, Roberto, this is impossible for me to specify. Even with a list of your equipment, I cannot tell you what you will like. Room integration and taste still come into play and more importantly you have not indicated what it is about your current system, or the BDA-2 in particular, that you like or dislike, or which direction you want to take it. This leaves me with no clues to go on.
Please understand that especially in this price range there is no such thing as a product that is “absolutely better” than any other, on all aspects, in all occasions and to all people. Both the Bricasti and the Aqua are great but cater to different tastes. I think I have explained very clearly how these two DACs sound. It is now up to you to judge which of the two you would like to add to your system.
Ok Christiaan,
I thank You again for the advice, and to answer I can tell you that I am satisfied with the sound of my system, and that the room has no problems, mine is just an attempt to grow the overall quality, replacing my already well played dac with a model of absolute level. My confusion arises from reading about the choice between the Delta-Sigma and R-2R conversions, and the fear that Delta-Sigma is an outdated technology in which it is not worth investing for a high-priced DAC.
” Listening ” audio devices through articles is complicated 🙂
Sorry my poor English.
Hi Roberto, No worries about your English, I understand you just fine:-)
Yes, indeed the decision between Delta/Sigma and Multibit is an important one. However, very many high-end brands are using these chips now. Multi-bit has become really rare. That said, I still find that Multibit has more energy to it, resulting in a more direct and lively sound. The Aqua is more like the Wadia 521 in that regard (the last “real”, multibit Wadia), but more like the Bricasti in terms of refinement and resolution, and therefore, if you want to retain your overall balance, probably the better successor to your Bryston than the Bricasti would be. I think this may be the answer you were looking for?
Many Thanks Christiaan, I will think a little more and then I will make the choice. I’m sure I will not be disappointed by the dac that I will buy ….because I will not listen to the other one … 🙂
Haha, quite right:-)
Hi Christiane, thinking about DACs I rarely found reviews on Bryston BCD3 and Hegel Mohican: both dedicated DACs designed only and for CD 16/44.1KH. Vantages,Disavantages ….May be you can bring in a little “light” about.Thanks.Andrés-Spain,
I’ve not heard the Mohican so I cannot comment on how it would compare to the BCD-3. I do know the BCD-3 and I like it a lot. What hifi’s comment “Bass lacks a bit of bite and scale” does not make sense to me at all. This player has bass that is solid, fast and dynamic, almost Wadia-like… Please, do place comments under a related article, in this case for example the BCD-3 review would have made a lot more sense than the Aqua DAC.
I don´t focus on comparing BCD3/Mohican ,but on comparing a few DACs designed specifically for CD format and the rest which follow the current mainstream.
Thanks, Andrés
I am wondering if you have in mind to review the La Scala MK II Optologic version. From your reviews of the Ayon hybrids I would think that the sound of its tube/MOSFET design might be up your alley even more than it’s non-tube Formula XD version.
Also, I think it’s unfortunate that Aqua doesn’t include a preamp section with their dacs. I note that with the Ayon Stealth you found the combo better than the dac alone with a separate preamp, and from a practical point of view it cuts out those of us who want to drive an amplifier (or active speakers) directly – and need a remote to do it! Given that a separate preamp will alter the dac’s sound, I wonder if their decision is really driven by sound purity or cost issues.
I will be reviewing La Voce soon but for the La Scala, I have no plans just yet. I’ll see if I can fit that one in as well. Indeed I also find it would have been so much more convenient if the Aqua DACs had volume control, even if only passive, although that method has its own disadvantages. I can only speculate as to why they don’t include preamp sections but I assume that it is not about cost and rather because they just want to focus on digital and indeed the purity of the signal.
Thanks for the reply. It would seem worth asking Aqua about the preamp/remote issue, since without one they have no control over what’s used to complement dacs – tubes or straight digital. And they do put out a hybrid dac, so pure digital wouldn’t seem to be the reason. I thought it might have to do with the commonly deleterious effects of a volume control, but that’s just passing the buck.
Hi Gene, I asked Cristian Anelli of Aqua why they do not include volume controls. He replied: “We do not love the digital decoding (of digital volume control) and we believe in the match of top-class level preamplifiers with pure analog volume control.”
Hi Gene, as it turns out, I can review the La Scala DAC next month.
Great. Look forward to it.
Thanks, Christiaan. Not surprised. Some users of the Directstream dac have also noticed this too, which has been solved around by dimming the LED screen to black, either by setting or remote.
I noticed in one of the dac reviews that you went back to the Ayon Stealth for comparison, as if you’ve been keeping it around for its satisfying sound. What I’ve been curious about are the sound differences you hear between it as dac/preamp and the CH Precision dac/controller and the Aqua ones (the latter’s ladder dac you compared in the Stealth review, but it didn’t read like the comparison was to the Ayon dac/preamp combo, just the dac). I ask because the CH and upper Aqua are out of my price range (esp. in the States), but hearing your descriptions gives an idea of what one might expect. Thanks,
Hi Gene, indeed, I keep the Stealth around because I really like it. I currently use it as an analog preamp when playing records in the main system. The Ayon’s outputs in that case are patched directly to the CH A1.5 amp. It also comes in handy whenever I need an analog preamp for review purposes, for instance when comparing DACs that do not have volume controls. While the Stealth sounds bold and powerful and it possesses that midrange magic that really only tubes seem to be capable of, it is not the most transparent sounding preamp. That’s why I don’t want to use it permanently in the main system, not for digital use, anyway. Maybe I haven’t found the perfect preamp yet but, so far, I find the C1 DAC to sound best directly to the A1.5 power amp, so without a preamp inbetween. I have not compared the Stealth as a DAC+Pre to the CH C1 directly because, so far, the latter has always come out winning and I don’t feel that there would be much value in doing so anyway since the two products are in such different price classes. Nevertheless, it might be an interesting experiment! When I have some time I will do so and add this to the Stealth review.
Thanks.. I asked because In my set up, with a modified Oppo 203 as source, I’ve skipped the preamp and feed active ATC SCM19A floorstanders and JL Audio e-110 subs directly from a dac, currently the DirectSteam. It’s very nice sounding, but it does teeter on the edge of sounding digital, depending on the recording.
I can see your point but if you like the sound of the DS you might need to re-adjust to the sound of the Ayon Stealth as it has a very different character. Maybe adding a preamp could be a simpler solution? (I almost wrote Soulution… slip of the keyboard). Please don’t hold your breath for my test to appear as I have several other reviews in the pipeline that need to be completed first.
No hurry. My goal has been to keep things as simple as possible, hence the appeal of a dac with (remote) volume control or a dac/preamp combo, but alas I’m running up against what developers have in mind (the Oppo 203’s mod eliminated the analog section, even if its volume control provided satisfactory SQ). Hence why my thoughts about a Stealth or Stratos instead of the added cost and hassle of a finding a “right” preamp and cables. But I am open to suggestions in the latter’s spirit that would mesh well with the Directstream.
Thanks for the La Scala review, which sounds intriguing, although it would still require a good preamp. Thanks,
Hi Gene, I compared the Stealth to the C1, both as DAC/preamp. All the details are added to the Ayon review.
Hi Christiaan
Do you have any experiences with Lampizator DACs?
I would like to try an R2R DAC like the xHD and own a Golden Gate mit 4 x 300b now.
No idea if the R2R technic from the Aqua is the bringer or the tube output stage from the Lampi??
I like the sound from the GG, perhaps I should search for a used GG with R2R??
Best regards, Reinhard
Hi Reinhard, I’ve no experience with Lampizator yet but based on the tube versus transistor DAC comparisons that I did, I would think that the Formula xHD will sound quite different from the DAC you’re using now. I have compared the xHD to the La Scala mkII and the latter’s tube output definitely provides a different dimension. As it is the most transparent and highest-res DAC that I have heard yet, the Formula xHD will likely surprise you in certain aspects but whether you will like the different presentation I’m afraid only a direct comparison could unveil for you.
Reinhard — The new design – I’m forgetting its designation – can be built as R2R or with tube rectification as an option. That applies to the Atlantic TRP, which I have, and I believe to the GG as well. I know that one of Lampi’s No. American reps prefers the R2R sound, and I wish that I had been able to compare the two. Lampi itself and Lampi owners – see What’s Best forums – would presumably be the best sources of info about this.