{"id":13241,"date":"2017-12-31T22:17:23","date_gmt":"2017-12-31T20:17:23","guid":{"rendered":"http:\/\/www.hifi-advice.com\/blog\/?p=13241"},"modified":"2021-04-19T12:50:40","modified_gmt":"2021-04-19T10:50:40","slug":"aqua-formula-xhd-dac","status":"publish","type":"post","link":"https:\/\/www.hifi-advice.com\/blog\/review\/digital-reviews\/spdif-dac-reviews\/aqua-formula-xhd-dac\/","title":{"rendered":"Aqua Formula xHD DAC"},"content":{"rendered":"

State of the art NOS R2R ladder DAC with DSD compatibility<\/h2>\n

Review sample supplied by Aqua
\n<\/a>Retail prices in the Netherlands (incl 21% VAT):
\nFormula xHD: 13.670 euro
\nUpgrade from Formula to Formula xHD: 1085 euro ex shipping to the factory in Italy<\/h4>\n

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<\/a> 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<\/a> DAC.<\/p>\n

It was mainly due to my then Apogee Diva<\/a> speakers’ behavior that I could not stick with the Mosaic DAC and settled on a Wadia 521<\/a> 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<\/em> enough to really bring these speakers to life.<\/p>\n

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.<\/p>\n

Before I dive into the listening aspect, though, first let me explain some more about the Formula xHD DAC.<\/p>\n

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Formula<\/strong><\/p>\n

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.<\/p>\n

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Optologic<\/em> is what Aqua calls their DAC system, which uses multi-bit technology as used in their La Voce\u00a0 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.<\/p>\n

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Formula xHD<\/strong><\/p>\n

The Formula DAC has been out for a few years but was recently updated to Formula xHD<\/em> status. Compared to the Formula DAC it now includes new optimized firmware for the main FPGA and a new hybrid architecture USB board\u00a0with fully-floating (isolated) USB decoding and clock generation by FPGA with proprietary code. Finally, the upgrade also added full DSD compatibility.<\/p>\n

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Below are some of the most important features:<\/p>\n