The Optologic R2R conversion system aqua believes that the more musical D/A conversion system is based on the circuit usually identified as "resistor ladder". This technology has been substituted in the mass-market by the so-called sigma-delta converters. The sigma-delta converter is a near-completely digital circuit and for this reason it can be can be integrated on silicon and produced at low-cost. A quality resistor ladder DAC instead uses a circuit based on a set of high precision discrete resistors: at least 2 resistor banks, one for each stereo channel. The Formula DAC is the first in the aqua’s production to show a proprietary D/A conversion system, that we name Optologic. The signals sent to the resistor ladders are generated by a proprietary digital circuit, implemented inside an FPGA (Field Programmable Gate Array). Formula has a sign-magnitude converter structure, and this requires not two but four 24 bit resistors banks, each one made of very low tolerance discrete resistors. In order to separate the digital section from the sensitive analog circuits, galvanic and magnetic isolations are implemented between the FPGA and the four branches of the R2R ladder converter. This creates complete isolation of all digital circuitry - including the clock - from the analogue section, for a clean, noiseless ground plane. It also plays the main role in the differential management of the R2R ladders, achieving perfect symmetry between the counter-phase halves. The result is the highest tonal contrast and naturalness.
Pure 1x native sample rate DAC The Formula, like the other aqua models, is a digital filter-less DAC. Our conviction is that in spite of the instrumental measurements showed by upsampling / oversampling DACs, they rarely are able to produce the same emotional and realistic results.
A third important aspect in the aqua production is the modularity of the various electronic circuits. aqua equipment are not short life products: as modular, they are open to future improvements and to follow the evolution of the technology. Formula is made of a set of circuits every one developed on a separate printed circuit board easily interchangeable. As an example, each of the four resistors banks of the converter is separate and mounted on connectors.
State of the art digital and analog electronics As explained before, the Formula DAC uses no digital filter or any other compensation, relying instead on maniacal attention to each sub-circuit. The separate analog and digital power supplies are executed purely by extensive use of discrete BJT, Mosfet, J-Fet 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 electrolytic capacitors, all other caps are Tantalum, solid-polymer OS-CON and double-metalized MKP. The signal path itself is direct-coupled and completely capacitor-free. The two output stages (one single-ended, one transformer-coupled balanced) use discrete BJT and J-Fet with metal-film resistors. All the electronics parts show an ultra-low RF noise. An advanced ARM microcontroller manages the user interface on the front panel, the IR remote command and the communication port (serial, RS232 standard).
The xHD update This update has required significant optimization of code for the main FPGA of R2R ladder DAC which has improved sound quality.
The new hybrid USB XMOS xCore 200 (dual core) + FPGA circuitry enables the high-resolution file playback up to 768kHz PCM and up to DSD256 (Quad DSD)
xHD improvements: • Proprietary hybrid 2-stage XMOS xCore XE216 + FPGA • Fully-floating (isolated) USB decoding and clock generation by FPGA with proprietary code • High quality, long life, low noise parts and modular design that distinguish aqua - acoustic quality equipment • 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)
• Proprietary Optologic D/A conversion system. Pure R2R ladder - FPGA (Field Programmable Gate Arrays) based without digital filter
• Galvanic and magnetic isolations between the FPGA and the four branches of the R2R ladder converter
• Jitter free digital interface AQlink PRO (I2S protocol), uncompromising digital connection to La Diva cd transport
• Discrete R2R ladder DACs with low noise precision resistors
• Zero S/PDIF Jitter design, digital receiver stage PLL (phase locked loop) technology
• High-performance AQ Discrete Regulator (MOSFET, J-FET, BJT) for analog and digital DAC’s power supply
• 2 separate low noise C-Core power transformers, one for the analog and one for the digital section
• MODULAR DESIGN with upgradeable multi board platform
"With the original La Scala 2 being one of my two reference converters and the top deck in contributor John Darko's DAC index, exploring audible space beyond it seemed, truth be told, a rather tall order. How much room was there left for improvement? What ungodly reference gear would it take to hear it? As it turned out, the Formula delivered a demonstrable lead with €6'500-class ancillaries like a Pass Labs XA30.8 or pair of Zu Audio Druid V speakers. If you're an audio aboriginal who goes deep walkabout into gargantuan soundstages to cherish size, scale and utmost specificity about recorded space, this Italian formula has your number. But it's not merely about the usual 3D markers and how precisely and widely spaced they are. It's about an added dimension. That accesses the emotional mood or climate of the playback scenery. Whilst costlier decks came through earlier, none of them did it at that potency. Granted, to fully matter relies on superior recordings. Lesser or purely synthetic efforts reveal that they lack that particular magic. Finally there's this peculiar easy-digital aspect as though your brain's usually active aural processor went on holiday because it's not needed. As such, I must highlight Aqua Hifi's Formula with one of our sparsely administered awards. True, it's serious money. But it's seriously well built. And it delivers very serious performance. Yet all this multi-stage seriousness melts away when one is faced by such deep holistic listening satisfaction. That's what the 'high' in hi-end should be all about. Cachet, pride of ownership, resell value and bling to impress the ignorant with all factor. But they pale to nothing against delivering the actual experience. The Formula does. So it pays to study its recipe in detail. It really is something else."
X Core Driver on Windows OS (W7, W10) for new Frormula xHD
"The great thing about the Formula xHD DAC is that it offers unprecedented purity and all the advantages of the aforementioned R2R designs and adds to this all the dynamic power and drive that I could ask for, while totally avoiding imposing any character onto the sound." "But in the end all the technology in the world means nothing if it does not distil into great sound. Fortunately, after having heard the Formula xHD DAC, I can testify that this DAC is truly magnificent!"
Christiaan Punter of HIFI ADVICE: “WOW”, this is a seriously great DAC!
"Aqua Acoustic Quality’s Formula xHD is an extremely fine-sounding DAC whose warmth and ability to decode files of extremely high resolution should win it many admirers. Many will also applaud its designer’s rejection of digital filters, oversampling, upsampling, and MQA. Thanks to the Formula xHD’s ability to smooth over digital’s rough edges, I don’t hesitate to recommend that it be auditioned by anyone with $17,000 to spare, and whose system suffers from bright or harsh sound, or who values, above all else, the warmth and bloom often ascribed to analog sources."
Jason Victor Serinus Stereophile - June 2018
Jason Victor Serinus | Stereophile: “Formula xHD is an extremely fine-sounding DAC”
"The best sound at CES-indeed one of the best sounds I’ve heard at a trade show- undoubtedly came from the big, $191k, three-and-a-halfway (two 1" diamond tweeters, two 7" Omega 7 midrange drivers, and two 11" Nomex-Kevlar woofers in a D’Appolito configuration) Kharma Exquisite Midi Grand Signature floorstanders, driven by Lamm Industries’ ML3 Signature monoblock amps, LL1.1 Signature preamplifier, and LP1 Signature phonostage, sourced by a TechDAS Airforce 1 turntable (with SME 3012-R tonearm and Clearaudio cartridge) and an Aqua La Diva transport and Formula xHD DAC, and wired by TchernovCable. Housed in a large room on the 35th floor, this sensational system was spacious like nothing else at the show-and gorgeous like nothing else at the show, producing a supremely beautiful sound wherein everything was in balance, everything was exquisitely defined (though not over-controlled), everything was imbued with lifelike bloom and color.... it was worth coming to Vegas just to hear this system. "
The "Greatest Bits”, new award for the Formula DAC
The Mono and Stereo Upper Echelon Product Award
"Ladder DACs have revived my interest in digital few years back and it was quite a shift for an analog guy who couldn't stand the digital for more than few minutes."
"The Formula Xhd DAC encompass THE very attributes of 21st century high-end audio digital replay with the "set of skills", that were unthinkable few years back. I'm talking about sound quality without even entering the price point."
"Acoustic Quality Formula Xhd DAC has now climbed up the ladder and reached the plane, where the sense of realism is more closely mimicking the real thing."