In Barn: Aqua Formula Optologic DAC

The Aqua Formula Optologic DAC ($14,000).

From Aqua HiFi:

The Optologic R2R conversion system
AQUA believes that the most musical D/A conversion system is a "resistor ladder" circuit.

This technology has been substituted in mass-market DACS by sigma-delta converters.

The sigma-delta converter is a near-complete digital circuit and for this reason it can be integrated on silicon and produced at low-cost.

A quality resistor ladder system by contrast uses a circuit based on an array of high precision discrete resistors: at least 2 resistor banks, one for each stereo channel.

The FORMULA DAC is the first in AQUA’s history to implement a proprietary resistor ladder conversion system we call OPTOLOGIC.

The signals sent to the resistor ladders are generated by a proprietary digital circuit, programmed inside a FPGA (Field Programmable Gate Array).

In order to separate the sensitive analog circuits from the digital section, galvanic and magnetic isolation is implemented between the FPGA, and four branches of the R2R ladder converter.

This achieves complete isolation of the entire digital circuit - including clock - from the analogue section resulting in a clean, noiseless, ground plane.

It also serves a critical role in the differential management of the R2R ladders, creating perfect symmetry between the counter-phase halves. The result is the highest tonal contrast and naturalness.

The FORMULA has a sign-magnitude converter structure which requires not two but four 24-bit resistor banks; each one made with low tolerance discrete resistors.


Sample Rates Supported AQlink / I2S serial bus – USB PC Audio : 24 bit / 384 Kh, DSD/64 & DSD/128
S/PDIF – AES/EBU : 24 bit / 192 KH
Supports DSD via DoP on all inputs
Asynchronous USB (High Speed) USB Type B
Digital Receiver PLL (phase locked loop) technology 128 or 256 FS selectable
AQlink (I2S bus) LVCMOS level
Digital to Analog Conversion type Proprietary Optologic DAC
Oversampling Factor 1x
Analog Conversion Method Pure R2R ladder—FPGA (Field Programmable Gate Arrays) based digital decoding without digital filter
Digital Inputs
  • RJ45 AQlink (I2S serial bus) – 24 bit / 384 KHz – DSD/128
  • BNC coax (S/PDIF) 75 Ohm – 24 bit / 192 KHz – DSD/64
  • USB port – 24 bit / 384 KHz – DSD/64 & DSD/128
  • Modular input:
  • AES/EBU balanced 110 Ohm – 24 bit / 192 KHz – DSD/64
  • RCA coax (S/PDIF) 75 Ohm – 24 bit / 192 KHz – DSD/64
  • AT&T (ST Fiber) – 24 bit / 192 KHz – DSD/64
  • Optical TOSLINK – 24 bit / 96 KHz
Analogue Outputs UNBAL 2 RCA Output 2.4 V RMS
BALANCED (passive transformers symmetrical) 2 XLR Output
Output Impedance 3.8V RMS
Load Impedance 10 Ohm RCA – 600 Ohm XLR
10 kOhm (min.) RCA – 600 Ohm XLRS
Frequency Response 20Hz to 22kHz +0.5dB/-0.5dB
THD + N < 0,016% 1KHz -10dB
Main Processor STM-ARM microcontroller
Control Connectors 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 – 82VA
Dimensions ( W x D x H ) 450 x 380 x 100 mm
Weight 9 kg
Front Finish Satin Alu Silver or Satin Black
Case finish Grey Nextel powder coated