The astute reader took note of the 'super' symmetrical circuit. She probably suspected that the FPGA meant glue logic for non-audio R2R chips à la Metrum Acoustics. Actually, "there are no DAC chips, only R2R ladders executed with discrete precision resistors which are separated from the field-programmable gate array via optocouplers". With that, Aqua Hifi join the small band of merry R2R diskretniks like Aries Cerat, LampizatOr, LessLoss, MSB, Rockna Audio, S.A.Lab, TotalDAC and Wagner Audio who build their own ladder-type converters one resistor at a time. Unlike the former range topper LaScala MkII, the Formula has no tubes. That reiterates how Cristian Anelli isn't married to any given tech. He uses what works best for a given application. The breakdown of this formula was beginning to look most interesting. "Over our prototype R2R network without galvanic isolation, the 'optologic circuit' improved its performance. This became a one-step solution with dual benefits: perfect symmetry for the R2R network; and a true analog ground."

For connectivity, the Formula's six toggle-selected inputs correspond to AES/EBU on I, BNC on II, coax on III, modular (AT&T ST fibre, I²S, AES/EBU, coax or BNC) on IV, USB on V and AQlink/I²S on VI. The 9 pin D-SUB for the RS232 interface serves home automation, PC remote and such. "Our main micro controller is an advanced ARM STM32." Now we get Optologic DAC. Given the unexpected twin benefits of optocouplers between digital input stage / housekeeping FPGA and where conversion to analog happens in balanced resistor ladder pairs, optical isolation was the next logical thing. To give credit where due, Cristian added that "it is a pleasure to let you know that I designed the DAC's discrete FPGA conversion and STM32 micro controller in collaboration with engineer Gianfranco Meneghetti. He has more than 25 years of experience in the electronic industry working for various companies like ST Microelectronics, Ascom Safnat, Samsung Electronics Italia, Jabil Circuit and Teradyne. Gianfranco is great." A day after the Munich show, "I'm in the tunnel of the Optologic DAC upgrade project for the La Scala MkII." Cristian wouldn't rest on his laurels but shine more light—isolation by optocoupler—on his earlier models? "La Scala will have the same proprietary discrete R2R ladder architecture as Formula." How would Formula differentiate itself against La Scala MkIII? "The FPGA and logic parts will be the same but Formula gets costlier R2R resistors and a more sophisticated power supply for its DAC section. The LaScala will retain its hybrid tube/Mosfet circuit with the ECC81."*

* The retail price of a La Scala MkII Optologic DAC is €6'600; or a revamp charge of €1'000 for owners of an original MkII which will require shipment to the Italian factory for the conversion.

Here it's fair to be reminded. Unlike most DAC fabricators, Aqua are a more complete digital provider. They continue to support disc spinning with their dedicated La Diva transport. It's one of the potential I²S-over-CAT5 senders for their DACs' AQlink inputs. Below we see a short assembly line of transports at left; and at right Cristian's prototype white circuit boards of the Formula during a bug exorcism prior to the Munich HighEnd 2016 show.

Removing 12 hex bolts with additional plastic contacts to protect the cover's Nextel paint revealed unbelievably well-built innards executed with multi-stacked modules for non-obsolescence. Below we see the central housekeeping DSP board to the left, then three of the four discrete resistor ladder boards, with the vertical single-ended outboard module at the far right.

Next comes a view of the power supply board with its high-current jumper connections from the twin transformers.