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ANKits DAC 2.1 Signature DAC

ANKits DAC 2.1 Signature

This is a rare bird in the pages of TAS—a kit report for the intrepid DIYer, who’s in search of an affordable DAC and not afraid of wielding a soldering iron. Well, to be more specific, my report is strictly about the sonics of this DAC since I purchased the unit fully assembled. Yes, this is an Audio Note UK (AN) design. But while originally the kit business was integrated with AN’s finished-product side, in 2004 it was shut down internally due to the support-heavy requirements and low margins of kits. It was then that Brian Smith approached AN’s president, Peter Qvortrup, with a proposal to keep the kit business going, and the end result was ANKaudiokits.com. To avoid confusion, the branding was changed to ANK or ANKits. By 2014, after many regular engineering trips from Canada to the UK and lots of AN part purchases, the kit business was taking on a life of its own, with a full range of products including EL34, EL84, and 300B amplification, phonostages, preamps, and DACs. It’s absolutely brilliant that ANK can leverage Audio Note’s engineering and parts development for DIYers, who can thereby approach the AN sound at a lower price point.

The $1700 DAC 2.1 kit is considered an entry-level product, but is one of ANK’s longest running products with a significant DIY following. It has seen several variations, though currently production is only focused on an upgraded version known simply as the DAC 2.1 Signature. As Brian puts it, ANK basically sends out a box of parts, and 50% of the success is ultimately in the customer’s hands. The one exception is the digital board, which is supplied fully assembled. As with other kits, the customer has total freedom to experiment in wiring, capacitor choices, and tube-rolling to tailor the sound to his liking. It needs to be emphasized that ANK is not in the business of manufacturing finished products, though they do occasional build for U.S. customers for a reasonable surcharge.

As I survey the past 40 years of digital audio and consider the sonic carnage inflicted by so many DACs and CD players, I am reminded of the title of Don and Carolyn Davis’ book, If Bad Sound Were Fatal, Audio Would be the Leading Cause of Death. Having suffered through a multitude of excruciating digital products, I was almost ready to fully retreat into the soothing world of vinyl. Eventually, the art got better, and, to my ears, a key element was the embrace by some manufacturers of R-2R DAC technology with no oversampling (NOS) digital filters. Audio Note did much to popularize this approach. In fact, the kit’s digital board doesn’t even have an anti-aliasing analog filter.

ANKits DAC 2.1 Signature DAC

The digital board is outfitted with an Analog Devices AD1865 dual-18-bit stereo DAC chip. It was introduced in 1991 and has by now been designated obsolete by Analog Devices, not an unusual outcome for R-2R chips of that era. That’s actually a shame because in the early 1990s R-2R DAC technology had come of age through the use of segmented DAC architecture to reduce glitching at major digital code transitions. Partial segmentation was incorporated on the AD1865 by separating out the first four most significant bits (MSBs) of each DAC and segmenting them into 15 resistor elements with their own logic. The 14 remaining least significant bits (LSBs) were converted using a standard R-2R ladder. The expense in manufacturing was driven by laser-trimming both the segment and R-2R resistors to provide extremely low total harmonic distortion.

The AD1865 can accommodate up to a 24/96 data stream. That means that it cannot handle high-res 24/192 PCM data. In addition, being an 18-bit DAC, the AD1865 will truncate bit depth from 24 bits down to 18 bits. There is nothing to worry about if you’re spinning CDs or streaming 16/44.1 files. But how important is the six LSB bit-depth loss during playback of 24/96 or 24/48 PCM files? Theoretically, greater bit depth increases dynamic range, and on a good recording that should push the threshold of audibility closer to the recording’s noise floor. As a result, delineation of transient decay and hall ambience should both improve. Could I hear the difference? Well, it was subtle, but I thought so. For example, streaming Miles Davis Kind of Blue at 24/96, I did notice a slight loss of ambient detail through the DAC 2.1 when compared with the more expensive 26-bit discrete R-2R Denafrips Terminator DAC reviewed in Issue 316. However, to be fair, it isn’t clear if the differences noted are strictly assignable to bit-depth reduction or influenced by the current-to-voltage converter or the output stage. That would be tubes in the case of the DAC 2.1 and solid-state for the Terminator. 

The ANK DAC is a tube aficionado’s dream come true. For starters, the high-voltage power supply is tube rectified as well as tube regulated using an ECL82 pentode-triode configured as a shunt regulator. The power supply represents an enhanced version of Audio Note’s original M2 design taken from its finished product line. It includes a beefy power transformer and a capacitor-choke-capacitor filter network using Rubycon electrolytic caps. The AD1865’s current-output-to-voltage conversion is accomplished via a pair of custom transformers, which couple the signal to the analog driver board. Voltage amplification is performed by a pair of 6922 dual triodes, one per channel, each of which is configured as an SRPP stage. Output coupling caps on my unit were Audio Note copper-foil types. The DC filament supply for these tubes is also regulated. 

My DAC was shipped with JJ Electronic 6922 tubes, which make for a decent starting point, though they do require a minimum break-in period of about 20 hours. After a few weeks I decided to roll in a pair of Amperex 6DJ8 tubes (orange globe logo). And that resulted in a dramatic sonic payoff. In hindsight, it became clear that the JJ is a pretty boring tube, at least in the context of the ANK DAC. The Amperex yielded greatly improved dynamic contrasts, resulting in a significantly livelier boogie factor. Tonal colors became more vibrant. Harmonic textures gained in delicacy, while the treble range perceptibly opened up with a greater sense of space. In all, the Amperex 6DJ8 proved to be a truly worthwhile investment. 

I decided to forgo the optional USB input, since my intention all along was to deploy Matrix Audio’s exceptional SPDIF-X 2 USB interface to convert the USB data stream off my laptop to SPDIF format. This is a Class 2.0 asynchronous digital interface based on the XMOS U208 chip, with a built-in high-quality femtosecond clock and FPGA processing unit. Initially, that is before the arrival of the iFi SPDIF iPurifier2, streaming off my hard drive and Qobuz through the Alldaq ADQ-USB 3.0 isolator and the Matrix Audio USB interface proved superior to direct SPDIF input off my transport. 

Before the iPurifier2, direct SPDIF input lacked imaging precision, clarity, especially through the treble range, and most importantly for me, timbral fidelity of soprano voice. The ANK’s onboard digital audio receiver, an industry-standard Crystal Semiconductor CS8414 chip, wasn’t apparently able to cope with the jitter produced by my CD transport. Enter the iPurifier2. Connected between the CD transport and DAC, right at the ANK’s SPDIF input, it was responsible for a radical enhancement in sound quality. It was now difficult to differentiate CD playback from USB streaming through the Matrix Audio interface. This latest version from iFi offers much better jitter reduction relative to the Gen1 version via a fast 10MHz master-timing femto clock. The SPDIF iPurifier2 is so good that it has become a permanent fixture in my playback chain. My purchase off the Bloom Audio website (bloomaudio.com) was a pleasant experience, so be sure to check it out.

Unlike so many DACs that manage to sound uninvolving, no matter how outstanding the digital circuitry, the ANK stayed true to its tube essence. That was both good and bad. The bad part was a concession in the bass range to the Terminator DAC, which clearly dominated in bass control. That was most evident on upright bass, which lacked the ultimate in pitch definition. But as compensation, tonal colors were nicely saturated and harmonic textures were silky smooth. I auditioned the ANK DAC in the context of quite a few preamps. A clear case of synergy emerged with all-tube units such as the Supratek Chardonnay, bringing about a liquid, lush, and lyrical midrange. The effect was so totally relaxing I felt as though I had been immersed in a warm bath. 

You may wonder if such a warm and luscious presentation obscured too much low-level detail. OK, so the ANK isn’t the most detailed DAC on the planet, but there was still enough detail being resolved within an organic musical tapestry that I didn’t feel cheated. In fact, I detest a hyper-etched presentation. My preference has always been for a natural flow of detail which closely mimics my concert hall experience.       

Plain and simple, I found the ANK DAC 2.1 Signature to be a reliable conduit of good sound. It allows the music to flow in a natural manner. Wave goodbye to digital brightness and washed-out tonal colors. Its limitations are mostly imposed by the choice of an 18-bit 96kHz DAC. It performs well with Red Book PCM data and doesn’t give away much with 24/96 PCM data. If like me your sonic priority is the midrange, then you can’t go wrong with this DAC. For me it proved to be a DAC made in heaven. 

Specs & Pricing

Output tubes: Two 6922
HV regulator tube: ECL82
Rectifier tube: 6X5
Digital inputs: 75-ohm RCA (SPDIF); optional USB
Analog output: Two RCA
Output level: 2.0V RMS both channels
Output impedance: 1.3k ohm
Dimensions: 38.1cm x 14.6cm x 40.6cm
Weight: 24 lbs.
Price: $1700

ANK AUDIO KITS
613-869-0011
ankaudiokits@gmail.com
www.ankaudiokits.com

Associated Equipment
Loudspeakers: Fleetwood Sound Company DeVille, Tannoy System 1000, Watkins Audio Gen Four
Digital front end: Audirvana 3.5 software, Alldaq ADQ-USB 3.0 isolator, audiolab 6000CDT transport, Matrix Audio X-SPDIF 2 USB bridge, ifi SPDIF iPurifier2
Power amplifiers: Ayon Spirit P/A, Linear Tube Audio ZOTL40 Reference, Red Dragon Audio S500, VTL Manley Reference Series 100/200 monoblocks, Air Tight ATM-300R SET
Preamplifiers: PrimaLuna EVO 400, Supratek Chardonnay, Blue Circle Audio BC21.1, Sonic Frontiers SFL1 Signature Platinum, Experience Music AVC, Ed Schilling’s The Truth
Cables: Mogami and Kimber KCAG interconnects; Analysis Plus Oval 12, FMS Blue, & Take Five Audio Cryo treated Mogami 3103 speaker cable
Accessories: Sound Application CF-X & TT-7 power line conditioners

Tags: DAC DIGITAL TO ANALOG DIY

Dick Olsher

By Dick Olsher

Although educated as a nuclear engineer at the University of Florida, I spent most of my career, 30 years to be exact, employed as a radiation physicist at the Los Alamos National Laboratory, from which I retired in 2008.

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