The Optologic R2R conversion system

Aqua believes that the more musical D/A conversion system is based on the circuit usually identified as a “resistor ladder”.
The so-called sigma-delta converters have replaced this technology in the mass market.
The sigma-delta converter is a near-completely digital circuit, and for this reason, it can be integrated into silicon and produced at a 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, requiring not two but four 24-bit resistor banks, each one made of very low tolerance discrete resistors.
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
Like the other aqua models, the Formula is a digital filter-less DAC.
Our conviction is that despite the instrumental measurements shown by upsampling/oversampling DACs, they rarely produce the same emotional and realistic results.
Modularity
A third important aspect of aqua production is the modularity of the various electronic circuits.
aqua equipment is not a short-life product: as modular, they are open to future improvements and to follow the evolution of the technology.
Formula is made of circuits developed on a separate printed circuit board that is easily interchangeable.
For example, each of the four resistor 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 for the best sonic result and their top quality, longevity and reliability. Except for 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 electronic 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 code optimisation for the main FPGA of the R2R ladder DAC, which has improved sound quality.
The new hybrid USB XMOS Core 200 (dual-core) + FPGA circuitry enables high-resolution file playback up to 768kHz PCM and native DSD512
xHD improvements:
• Proprietary hybrid 2-stage XMOS Core 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 DSD512
• Latest version of customised 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)
Analog module Rev. 2
A new level of sonic performance. The new boards implement new output transformers, specially selected super-fast active components and improved polarisation of circuitry.Formula xHD Rev. 2FEATURES• 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
• Transformer-based true balanced audio output stage
• Fully upgradeable high-speed USB hybrid 2-stage XMOS XCore XE216 + FPGA, Fully-floating (isolated) USB decoding and clock generation by FPGA with proprietary code
• Proprietary USB Firmware/driver:
Apple MAC OS – Linux OS: USB asynchronous native support, no need to install drivers software
• Digital phase selector on the front panel
• High-quality parts selected for sound quality:
– Tantalum, solid-polymer OS-CON and double-metalized MJP capacitors
– low noise Metal Foil ultra-precision resistors
– double metabolised film pulse capacitor
– ultra-fast diodes
– halogen-free cables
• Aluminium anti-resonant cabinet with Nextel
• RC5 IR remote controller (optional)
• Designed and handmade in Italy

Aqua Acoustics