Aqua Formula xHD Rev. 2 Optologic R2R Reference DAC

The Optologic R2R conversion system

Aqua believes that the most 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, and does not oversample the incoming signals.

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.

Modularity

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 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 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 metallized film pulse capacitor
- ultra-fast diodes
- halogen free cables

• Aluminum anti-resonant cabinet with Nextel

• RC5 IR remote controller (optional)

• Designed and handmade in Italy

Specifications

Digital to analog conversion type
Proprietary Optologic D/A conversion system
Pure R2R ladder - FPGA (Field Programmable Gate Arrays) based without digital filter

Supported Native Sample Rates
AQlink / I2S serial bus - USB PC Audio : 44.1kHz to 768kHz PCM up to 24 bits
DSD64, DSD128, DSD256, DSD512
Supports Native DSD via USB and DoP on all inputs

DAC architecture
Multibit sign magnitude R2R ladder (upgradable)

Asynchronous USB (High Speed)
USB Audio Class 2 with Type B connector

Digital Receiver
PLL (phase locked loop) technology 128 or 256 FS internally selectable

AQlink (I2S bus)
LVCMOS level

Oversampling factor
1x

Digital inputs
- RJ45 AQlink (I2S serial bus) - PCM 24 bit / 768kHz – DSD64, DSD128,
DSD256 via DoP
- BNC coax (S/PDIF) 75 ohm - PCM 24 bit / 192kHz – DSD64 via DoP
- RCA coax (S/PDIF) 75 ohm - PCM 24 bit / 192kHz – DSD64 via DoP
- AES/EBU balanced 110 ohm - PCM 24 bit / 192kHz – DSD64 via DoP
- USB port - PCM 24 bit / 768kHz – DSD64, DSD128, DSD256, DSD512
Modular input:
- AES/EBU balanced 110 ohm - PCM 24 bit / 192kHz – DSD64 via DoP
- RCA coax (S/PDIF) 75 ohm - PCM 24 bit / 192kHz – DSD64 via DoP
- AT&T (ST Fiber) - PCM 24 bit / 192kHz – DSD64 via DoP
- Optical TOSLINK - PCM 24 bit / 96kHz – DSD64 via DoP

Analogue Outputs
UNBAL 2 RCA Output 2.4 V RMS
BALANCED ( passive transformer's symmetrical ) 2 XLR Output : 3.8V RMS

Output Impedance
10 ohm RCA - 600 ohm XLR

Load Impedance
10 kohm (min.) RCA - 600 ohm XLR

Frequency Response
20Hz to 22kHz +0.5dB/-0.5dB

Phase Response
Linear phase

THD + N
0,016% at 1kHz 0dB

Main processor
STM-ARM microcontroller

Controls
9 Button on front panel, IR Remote, Isolated RS-232 D-SUB 9-pin connector

Front Panel
Power, phase invert, mute, input switch, RC5 remote sensor

Power Consumption
100-115V / 220-240V; 50 or 60Hz - 58VA

Dimensions
( W x D x H ) 450 x 370 x 100 mm

Weight
9 kg

Front finish
Satin Alu Silver or Satin Black

Case finish
Grey Nextel powder coated