Aqua Formula xHD

The Optologic R2R conversion system

Aqua believes that the more musical D/A conversion system is based on the circuit usually identified as the "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 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 analog 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. In spite of the instrumental measurements showed by upsampling/oversampling DACs, they rarely are able to produce the same emotional and realistic results.

Modularity

A third important aspect in the aqua production is the modularity of the various electronic circuits.

aqua equipment is not short-life products: as modular, they are open to future improvements and to follow the evolution of the technology.

The 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 native DSD512

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 DSD512

• 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)

Features

• 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 metalized 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