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Nagra audition room with Verity Audio Lohengrin II speakers.

The ultimate DAC would arguably need a dual-core engine: true 1-bit for DSD, discrete R2R for PCM. Nagra's current DAC project—something even more ambitious is in the works—nears completion. The team in Romanel-sur-Lausanne is firing on all cylinders. This spans from conceptual to mechanical, from multi-layer PCB layout to advanced power supplies, from analog and digital circuits to control logic, display coding, firmware authoring and more.

Anticipated to come in at ~€15.000 - €18.000 depending on PSU option, the first spin-off of Nagra's extreme DAC project is to be previewed as a prototype at the upcoming Munich HighEnd show next month. Final production will be housed in classic Nagra livery. Even so it'll sprout two outboard power supplies for digital and analog respectively since the compact trademark casing will be far too crammed with this signal-path circuitry, interstage and balanced output transformers plus two very large coupling capacitors and a valve to leave any room.

breadboarded DAC

Fully DSD64/128 and 24/384kHz PCM compliant, this as yet unnamed deck is based on a core module from Andreas Koch of Playback Designs as the ultimate authority on DSD. From him Nagra commissioned a custom ceramic board. The heart of its circuit is a Xilinx FPGA coded to operate as a true 1-bit DAC since commercial true 1-bit chips no longer exist.

'Jumper Central' for easy listening comparisons of various circuit or parts options during prototyping.

Everything before and after that small board is designed by Nagra's in-house team. They tap directly into Koch's analog reconstruction filter and follow it with their own ultra-precision chip-based impedance converters and drivers for each half of the symmetrical output. This direct-coupled stage applies no gain or feedback and operates with a colossal slew rate.

Next come ultra-complex Teflon-layered mu-metal enclosed interstage transformers with very thin primary wire and even thinner secondaries. They load the Koch module at a very specific impedance arrived at by careful listening.

These ITs sport extended bandwidth and linear phase response. After 12 prototypes which took Nagra's in-house expert half a day each to wind, engineering finally signed off on this challenging magnetic part with the bright blue metallic glass core.

These mono ITs generate passive voltage gain—+7/+11dB for 1V/2.5V outputs— further impedance conversion and signal summing since the Koch module outputs symmetrical but Nagra's circuit is single-ended. The ITs then see an auto-bias single mil-spec ECC82-related inverted triode buffer.

This US JAN valve benefits from special treatment on its larger plate, far lower microphonics, higher spec consistency and longer life expectancy over its common ECC82 equivalent. This cathode-coupled tube stage has negative voltage gain, no feedback but off-the-charts bandwidth. And its noise performance is better even than the ~130dB SN/ ratio of Koch's module. During my two visits the final coupling caps were giant silver/gold Mundorf issue because Nagra were still waiting for their very own custom Teflon/tin-foil equivalents.

4-in-1 MPS power supply (three AC supplies, one DC feed, LEDs still pre-production).

For Nagra whose chief PCB layout architect has worked in 16(!) layers for a previous military contract employer, the DAC boards here are very basic 4-layer affairs (two layers for signal, two for power supplies). Digital and analog grounds operate at deliberately different potentials. There are 22 dedicated power supplies with stout Elna Silmic 2 capacitive storage. Two of these are for high-speed USB alone to bypass buss power.

The MPS in bits'n'bobs. The case lacks the transformer, battery and battery logic board. The final production fascia shows the smaller now yellow LEDs marketing manager Matthieu Latour insisted on.

There are separate miniature isolation transformers for each of the two AES/EBU and two coaxial digital inputs plus three more for the 1GHz Ethernet-formatted I²S input. There's also a discrete headphone circuit, optional transformer-coupled fixed balanced outputs, remote-controlled analog volume for the RCA outputs and a menu-driven display for custom options like digital filter and fixed volume settings.

The type of stock Nagra PSU of which the DAC will get two (one for digital, one for analog).