Nagra’s HD DAC Archives

Nagra’s HD DAC Archives

Nagra’s HD DAC Archives

Nagra’s HD DAC Archives

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Reviewer:
Srajan Ebaen
Financial Interests: click here
Source: 27" iMac with 3.4GHz quad-core Intel Core i7, 16GB 1.333MHz RAM, 2TB hard disc, 256GB SSD drive, ADM Radeon HD 6970M with 2GB of GDDR5 memory, PureMusic 1.89g in hybrid memory play with pre-allocated RAM and AIFF files up to 24/192; Audirvana 1.5.10 in Integer mode 1, Metrum Hex, AURALiC Vega, SOtM dX-USB HD with Super-clock upgrade & mBPS-d2, Aqua Hifi La Voce 2
Preamp/Integrated: Nagra Jazz, Esoteric C-03, Bent Audio Tap-X, Crayon CFA-1.2, Bakoon AMP-12R, Gato Audio DIA-250, Job Pre2[on review]
Amplifier: First Watt SIT1, FirstWatt F6, Goldmund/Job 225, AURALiC Merak [on loan]
Speakers: soundkaos Wave 40 + Zu Submission, Albedo Audio Aptica, Boenicke Audio W5se, German Physiks HRS-120
Cables: Complete loom of Zu Audio Event, KingRex uCraft and Light Harmonic LightSpeed and Zu split USB cables, Van den Hul AES/EBU cable, Tombo Trøn S/PDIF cable, AudioQuest Diamond Toslink
Stands: Artesania Audio Exotyeric for front end, Rajasthani hardwood rack for amps
Powerline conditioning: GigaWatt power strip on amps, Vibex Granada on all components
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters
Room size:Irregularly shaped 9.5 x 10m open floor plancombines the living/listening room, kitchen and office. Added to this space the speakers see the air volume of the entry hall and a long corridor plus the 2nd-storey 6 x 9.5m loft. Wood-panel ceiling slopes up to the loft. Parquet flooring. Lots of non-parallel surfaces ('vertical gable' windows, twin-angle ceiling, spiral staircase enclosure, fireplace enclosure). For a pictorial tour, see here.
Review component retail in Europe [incl. VAT]: €19'900 with 2 x ACPS II power supplies; €22'900 with MPS and 2 x 1.25m DC cables, HD VFS €1'750 [for DAC], VFS €1'650 [for MPS]j


The ultimate DAC would arguably need a dual-core engine: true 1-bit for DSD, discrete R2R for PCM. Nagra's HD DAC—something even more ambitious was in R&D to explore viability of a dual-core circuit—neared completion by the close of 2013. The team in Romanel-sur-Lausanne was working hard to wrap the project. This spanned 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.


This spin-off from Nagra's secret extreme converter research project was previewed as prototype at Munich HighEnd 2013 but then still in a temporary box. Final production would adopt classic compact Nagra livery. Even though that builds out real estate by going considerably deeper than my Jazz preamp, it still sprouts two outboard power supplies for digital and analog respectively. That's because the trademark ¾ width low-rider casing is otherwise too crammed with signal-path circuitry, interstage and balanced output transformers plus two very large custom coupling capacitors and a valve to leave room for anything else.

Nagra audition room with Verity Audio Lohengrin II speakers.

Fully DSD64/128 and 24/384kHz PCM compliant, the HD DAC is based on a small core module from Andreas Koch of Playback Designs as probably hifi's 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. "The sampling frequency reaches 5.6MHz and the internal calculations use 72-bit precision. This method produces a signal with such quality that the steep-slope input filters on the analog section can be eliminated. The result is that the harmonics and transients are perfectly maintained, allowing the music to conserve its natural depth and essence."

Bread-boarded HD DAC prototype circuit during my April 2013 visit to Nagra.

The board in the foreground shows an early version of the Koch module.

'Jumper central' was installed for easy listening comparisons of various circuit and parts options during prototyping.


Everything pre/post the custom Koch board is Nagra's own They tap directly into Koch's analog reconstruction filter to follow up with their own ultra-precision chip-based impedance converters and drivers for each half of the symmetrical output. This direct-coupled stage applies neither voltage gain nor feedback but operates at a truly 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 which the listening team arrived at by careful auditions.


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 output is symmetrical but Nagra's circuit deliberately single-ended. The ITs then see an auto-bias single mil-spec ECC82-related inverted triode buffer.


This US JAN valve at the time was built with special treatment on its larger plate and offered lower microphonics, higher spec consistency and longer life expectancy over its common ECC82 equivalents. This cathode-coupled tube stage has negative voltage gain, zero feedback but off-the-charts bandwidth. Its noise performance is superior to even the ~130dB SNR of Koch's module. During my two visits the final coupling caps were giant silver/gold Mundorf issue because Nagra were still waiting on their very own custom caps.

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

For Nagra whose chief PCB layout architect has worked in sixteen layers for a previous military contract employer, these DAC boards are very basic 4-layer affairs (two for signal, two for power supplies). Digital and analog grounds operate at deliberately different potentials. There are 25 dedicated power supplies with stout Elna Silmic 2 capacitive storage and 32 decoupling capacitors. Two of the power supplies are for high-speed USB alone to bypass buss power.

The MPS in bits'n'bobs. The open case here still 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 true 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. Owners of multiple Nagra components can use the new MPS shown above. This eliminates running multiples of the compact stock power supplies shown below and centralizes Nagra power. Out of its four feeds the MPS runs one on pure battery power. The MPS can thus drive the HD DAC, Jazz or Melody preamp and a Nagra phono stage whilst only taking up a single wall or conditioner power outlet.

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

To better appreciate the gestation of any Nagra product, we'll now take a look at the team responsible for the HD DAC.

Otherwise empty prototype case at Munich HighEnd 2013 - in production one of the coaxial S/PDIF inputs became BNC.

Источник: [https://torrent-igruha.org/3551-portal.html]
, Nagra’s HD DAC Archives

Review: Nagra HD DAC; or, Closing the gap between digital and analog

Nagra founder Stefan Kudelski

There is not much to be said about Nagra Audio that has not been said already. The company goes back six decades, when Stefan Kudelski, a young talented engineer born in Poland but due to the second world war forced to move in Switzerland, after completing his studies in the Swiss Federal Institute of Technology in 1948 finally launched his first portable audio tape recorder.

The company remained an industry reference for portable audio recorders for decades, just consider that more than 10.000 Nagra III reel to reel tape recorders were sold. In 1997 Nagra finally released the first audiophile oriented product, the PL-P vacuum tube pre-amplifier followed in 1998 by the Vacuum Tube Power amplifier while their first audiophile DAC came out in 2003.

Very few companies can vaunt a pedigree of audio excellence like Nagra’s.

And you might think, how does all this heritage translate today. Put in just one word, it translates into music. I won’t tell you to go out and buy the Nagra HD DAC for one simple reason, it is pricey. But if you are in a hurry, the bottom line is this: Nagra HD DAC equals music.

The sturdy box screams classic Nagra lines, with the power knob sitting on the right side of the front panel, the iconic “modulometer” on the left, a two-line matrix screen next to it and the controller knob next to the volume lever. A headphone jack along with three small leverages (for the screen’s luminosity control, the option of switching the output to the headphones and for mute) complete the front panel. The round controller knob when pushed in enables the menu, so you can actually read and alter far more details than you might expect, including input selection, language, output level selection (there is selectable high and low gain output), phase, firmware version and how many hours are on the tubes (yes, tubes, will get back on that later on).

The headphone section makes only partially sense for this kind of product and I won’t be going deep into my analysis. Reason is simple, someone who can afford this kind of equipment chances are will be buying a standalone headphone amplifier and probably a good one too. For the record I gave it a try, and while timbre was spot on and music was highly textured, there was a driving issue with stubborn planar magnetic headphones. If, on the other hand, you have easy to drive headphones you might find out you don’t even need that standalone headphone amp after all.

The HD DAC is complete with both balanced and single ended outputs, a ground terminal, USB, I2S, optical, two AES/EBU inputs and two SPDIF, one with RCA connector, the other with standard BNC connector for true 75Ohm link. On the far right of the back panel there are two mini-LEMO connectors for the necessary power supplies, one for the analog circuit, the other for the digital section.

Back panel carries all the necessary connections

Built quality is superb, despite someone managed to bend the ground terminal before sending me the review sample. Nothing is left to chance, just consider that the footers (probably the best I have ever seen as standard on a piece of audio equipment) are made from non-magnetic copper-nickel-zinc non-ferrous alloy and sport a Delrin resin tip. For an additional grand and a half one can buy the specially designed, sand blasted, aluminum made bases that Nagra calls VBS (for Vibration Free Systems ) and place them (as they come in pairs) underneath the HD DAC. The base has some jelly like feet which in conjunction with the DAC’s footers made a perfect vibration isolation.

Bells and whistles (expensive ones)

Signal Projects Golden Sequence power cord, Das Klang USB cable and Nagra power umbilicals

As I said, those vibration bases come in pairs and my delivery package had four. If you were paying attention you must have noticed the two power supply inputs at the back of the chassis. Nagra provided the MPS external power supply for the HD DAC. An alternative could be a pair of ACPS II Nagra power supplies but if you want to do things properly (and trust me, you want) the Multiple Power Supply is the way to go. This external power supply is practically a necessity as the DAC it-self has no power supply at all, not even a small, auxiliary one. The MPS is slightly smaller than the HD DAC, looks and built quality are in  typical Nagra fashion. Now add another set of VFS base plates for the power supply. The sum of all this goes including Nagra’s umbilical DC cables would go north of 30.000 euros, divided into 23K for the HD DAC, 6K for the MPS and another 4K for the two sets of isolation bases. Fortunately Nagra offers the whole when sold as package at $29.995 and for that price you get the Nagra remote control and a pair of white gloves for handling the devices without leaving fingerprints behind for free!

Started my reviewing with standard (as in bloody cheap) cables, only to find out that the HD DAC craves fancy bells and whistles. A friend dropped by with an Argento power cord which made a significant difference on the overall performance and triggered an all-out cable assault. Off they went some industrial black power cords and my trusted Belkin Gold USB cable, in with Signal Projects Golden Sequence power python cord and exotic, as in made from vintage copper, Das Klang USB cable. In conjunction with my reference for more than a year now Black Cat Triode interconnects (exceptional value for money in Sommovigo’s designs) performance was elevated to sublime levels, though not before a small misadventure.

The devil hides in the details

The first three days were a reviewer’s nightmare. Reason was the HD DAC underperformed, at least for what I was expecting it to be. Yes, I was using a plain vanilla power cord and the Belkin USB cable but still, there was something not going very well as my Rockna Wavedream DAC was clearly better performing (and may I add at a fraction of the price). The Wavedream is a fantastic value for money, a ladder DAC with proprietary FPGA receiver and excellent master clock, not to mention it sounds detailed and natural at the same time. The HD DAC at first sounded rather constrained in dynamics and lacked inner resolution.

After giving a call to the local importer I was granted the opportunity to open the DAC’s case and check the interiors. My thinking was that the bump that bend the grounding terminal had wreaked havoc on the delicate circuits.

Nagra’s built quality is second to none, the sight of the internals was an audiophile’s oasis crammed with boards, custom Nagra and Duelund capacitors, hand wound interstage transformers and a single JAN 5963 double triode in the output stage. The conversion module was shielded under a gold metallic case, presumably for keeping it safe from EMI/ RFI along with curious eyes. Inside the golden cage lays a 72bit FPGA (field programmable gate array) chip capable of 2xDSD and 24bit/384KHz PCM playback.

Being there I decided to pop open the power supply as well, not much of a surprise there, Nagra quality was to be expected. The MPS outputs 4 separated 12V supplies meaning you can use it with other Nagra devices such as the CD player or the pre-amps. What appears to be an empty space next to the Nagra made toroidal transformer is the place where a Li-Ion battery fits. The provided sample was not equipped with the aforementioned battery, after all I was not planning on any field trips with 30K worth of equipment.

Actually a miracle from bellow. There was no obvious fault in the circuitry and I was getting nervous, could not understand why the HD DAC was not delivering. Sound was good rather than great and knowing Nagra, there is absolutely no chance they would have thrown a sub-par product on the market. The culprit was found accidentally, while swapping cables I moved the external power supply away from the DAC, down near my Raspberry streamer and all the sudden, fiat lux! Detailed and dynamic sound finally emerged from the DAC. Remember listening to Schubert’s Unfinished symphony  with Phillipe Jordan on the podium and thinking how dramatic his take is. I’m a sucker for modern, full of passion and drama recordings and the Wiener Symphoniker delivers in spades. Powerful crescendos and vibrant horns and bassoons make for a masterpiece of a composition and a judge of a system’s macrodynamic capabilities, the Nagra was finally alive and kicking! Those big swings on the second, andante con moto, movement were making me spring from my seat.

A month worth of music

Courtesy of the Nagra HD DAC, something like five or six weeks flew away. My Synology NAS is mostly packed with classic music but jazz is also covered with approximately 2000 quality titles which for some reason seemed highly appropriate for the Nagra HD DAC. Am I allowed to say that a component capable of transmitting jazz emotions can be for good reason called “musical”? Benedikt Jahnel, Antonio Miguel and Owen Howard made an exceptional work with their 2012 Equilibrium (ECM) full of rhythmic variations and contrasts between the piano, drums and double bass.
On the track Sacred Silence the HD DAC gave a perception of a big piano dominating the center stage while cymbals hovering above it. Imaging and soundstage were very good but most importantly the sound was yes, warm but not overly mellow. The Rockna DAC was a tad more neutral in comparison, providing only slightly more firm bass whereas the Nagra was more full-bodied. Tubes and interstage transformers are dangerous toys, in the hands of non-experienced engineers can end up creating syrupy results that make a fuzzy mess instead of music. Thankfully Nagra kept an exquisite balance between detail and warmth, with the end result being what we so often and for no good reason call “analog”.

In this case “analog” it is. Andreas Koch, known for his work with Sony and the SACD/ DSD format designed the conversion unit for Nagra which transforms all PCM incoming signals into 5.6MHz DSD. This begs the question, how good a pure DSD DAC is when playing DSD? Answer is quite simple, the Nagra HD DAC was the only DAC that made me search for more DSD titles up to now. Not that my Rockna did not handle them rather well, still there was no clear difference between titles in PCM and DSD, not one that would have me trying to expand my DSD library with passion. The HD DAC on the other hand offered a sense of ease, flow and lack of digital artifacts while playing Eden Atwood’s This is Always: The Ballad Session record that attracted me like only my turntable ever managed to.

No, the HD DAC is not a turntable and again no, it won’t take my Garrard’s place in the system. For the fun of it I played a few tracks in tight A-B comparison between my 401 fitted with Kuzma 4point tonearm, ZYX 1000 airy 3 MC cartridge, Signal Projects Apollon tonearm cable going straight to the ASR basis exclusive phono stage and while the results were close, the analog-analog set up had the upper hand compared to the digital-analog sounding DAC, at least with analog recordings and in terms of pace and timbre. With modern, digital recordings, the HD DAC was superior in terms of channel separation and detail retrieval thanks to the ultra-low noise floor. Reason why I rarely invest money on digital recordings pressed on vinyl, also reason why I wish the HD DAC was here to stay. Even if you are a hard core analog listener like yours truly, you still need a top notch DAC for what comes out nowadays.

A complete NAGRA HD DAC with matching power supply and isolation bases comes dangerously close to the $30.000 mark. This is a level that only a few years back was almost taboo for digital front ends; it remains so for many of us, which is worth a note, especially when so many capable DACs cost ten to twenty times less. The HD DAC after all is rather compact in size and might seem to many audiophiles a poor value.

Truth could not be more distant.

The internals are literally packed with boards and components placed in vertically; if those same components were laid out in “audiophile” fashion the case should have been twice as big. Second point, the quality of the components is unbelievable and expensive like few other products out there. The analog section of this DAC is tube based but very quiet, in fact Nagra says that it is even quieter than the digital one! Another reason for paying big money is the exclusivity of having a preeminent designer such as Andreas Koch working for you on what he knows best, DSD conversion on custom FPGA code. This is exclusivity for Nagra and not the same “code” you would buy if you were to pick his own Playback Designs DACs and players. Besides all this, one must add to the recipe a ten year guarantee and a brand name, Nagra, synonym of Swiss made precision.

All this would not be enough if the sound was not top notch, but the HD DAC from Nagra closes the gap between analog and digital.

Nagra HD DAC

  • Internal processing:  5,6 MHz, 72 bits
  • Compatible digital formats: PCM 24 bits up to 384 kHz, DXD, DSD x 2
  • Bandwidth: 5Hz to 40 kHz (+0 – 3dB)
  • Noise level: -128 dBr (linear)
  • Distortion: < 0.02% (at -20dBFS)
  • Digital inputs: 2 x S/DIF, 2 AES/EBU, 1 Optical, 1 Audio USB (mode 2), 1 x I2S (Nagra format)
  • Outputs: 1 stereo on RCA connectors, 1 stereo XLR (Symmetrical on transformers available as an option)
  • Dimensions: 277 x 350 x 76mm (12.2 x 13,7 x 3 inches)

MSRP

  • Nagra HD DAC with MPS power supply and VFS-L package $29.995
  • Nagra VFS-L $2.225
  • Nagra MPS $6.495
  • Nagra DC power cable 1.25 $495/ each
  • Nagra spike kit $350

Associated equipment

  • DACs and Headphone amplifiers: Rockna Wavedream, Chord  Mojo, LH Labs Geek Out 1000
  • Streamer: Raspberry Pi2 with linear PSU running Archphile OS
  • Local Network: TP Link Archer router with linear power supply, Synology DS216 NAS, Seagate Archive HDD with 128MB cache, Belkin Gold USB cable, Das Klang USB cable, Supra CAT 8 ethernet cables, Baaske medical grade Ethernet filter
  • Speakers: ATC Studio Control Monitors 100SL
  • Amplifier: ASR Emitter I HD integrated amplifier with external power supply, external battery
  • Akku and  phono module
  • Turntable: Garrard 401 in custom birch plywood plinth on top of a solid block of limestone for a total of 200+lbs equipped with NSC motor controller
  • Tonearms: Kuzma 4Point , SAEC 308L, SME 3009  S2 modified, Rega RB300
  • Cartridges:  MCs: ZYX  1000  Airy3 X  Low, Denon DL-102, Denon DL-103R, Fidelity  Research
  • PMC-1.
  • Phono stage: ASR Basis Exclusive, double board phono stage with external battery Akku
Источник: [https://torrent-igruha.org/3551-portal.html]
Nagra’s HD DAC Archives

Nagra HD DAC

There’s still a buzz about Nagra. Even those who have racked up a lot of miles on their audio clock get a little worked up over a Nagra product, and when that product is the first of the company’s new cost-no-object range, the long-awaited HD DAC, it’s hard to keep your feet on the ground.

Let’s get the aesthetics bit out of the way first: you have to be some kind of cold-hearted anti-geek not to love Nagra’s industrial styling. With the large recessed dials, switches, and that famous ‘modulometer’ on the front of both DAC and MPS power supply, the HD DAC has the classic look of a product made back when ‘built to last’ meant something. And yet, it’s not simply retro styling for its own sake; everything is there for a purpose. But regardless, it’s hard not to be impressed by the look and feel of these solid pieces of audio architecture.

However, it’s also important not to let the whole ‘it’s a Nagra’ element swamp the sophistication of what’s going on beneath that solid alloy case. This is a ‘back to the source’ digital project, leveraging years of professional digital audio engineering to basically start again with digital to analogue conversion. The professional audio side becomes apparent at the point of contact for a datastream; all the HD DAC’s digital inputs are filtered before being passed to a multiplexer circuit. This means the AES/EBU input on XLR and the S / PDIF inputs on BNC and RCA connectors each has its own individual transformer. This might seem like overkill to most digital companies because a digital datastream is not influenced by the impedance and level of the signal. However, the same does not apply to the electronics that process the datastream, and using the kind of best-in-the-business grade of transformers that Nagra can get for the task means the datastreams from each input are ‘presented’ to the digital processing section in the best possible condition.

Источник: [https://torrent-igruha.org/3551-portal.html]
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