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Digital to analogue converter

Price (in Poland): 26 000 zł

Manufacturer: Digital&Analogue Co., Ltd.

Contact: 4F, Bohyun Bldg. | 1458-4 Gwanyang-dong,
Dongan-gu, Anyang-si. | Gyeonggi-do | 431-060 Korea
tel.: 82-31-422-5690


Manufacturer’s website:

Country of origin: Korea Południowa

Product provided for testing by:
GFmod Audio Research

Text: Marek Dyba | Photos: Marek Dyba, Calyx Audio

Published: 2. March 2013, No. 106

It's been already a year since I reviewed Calyx 24/192 DAC (see HERE) and even though I still remember that device quite well and I still consider it very good sounding comparing even with many other devices I listened to later. Why, should you ask? Because it was the first D/A converter I knew that offered a higher quality sound from USB input than it offered from coaxial one. Today, a year later there are still very few on my personal list that achieved the same. Maybe that should not really be a surprise – designers improved coaxial input for many years, and their 'adventure' with PC-Audio and USB inputs started only (relatively) recently. In this industry achieving a perfection (or I should rather say something close to perfection) takes usually many, many years. It's a process that involves many designers, many companies, and the progress is achieved only step by step, and only after a long years of work such a brilliant device as also reviewed by me Accustic Arts DAC can be created offering amazing sound (from coaxial input to be clear). One of the pioneers of PC-Audio was an American company Wavelength that offered USB DAC before most other companies did, but today the competition has already grown strong. Many of manufacturers focus their efforts on creating so called USB converters or transports – devices that convert a signal delivered via USB to a standard that most DACs can accept via coaxial, AES/EBU, or BNC inputs. Fewer companies tried to create D/A converters that sport few digital inputs with USB being one of them and the goal was to achieve same performance regardless of the input used to deliver signal. To be honest so far only very few companies succeeded and Korean Calyx is one of them. Most likely few years back nobody even heard of this company (I mean outside Korea), and today, just 2-3 years later their USB DACs are among the best offered on the market. 24/192 DAC was, when I tested it a year ago, their top model, but than last year they presented a new flagship, called Femto. That’s w D/A converter obviously, but with build in digital volume control, which allows it to drive directly power amplifiers. 24/192 looked a lot like a miniMAC with both shape and size quite similar. But Femto is a true beast with its 18kg (!), and an extremely solid, aluminum casing measuring 430 x 102 x 404, and absolutely beautifully finished. There is nothing fancy about this casing – it's beautiful because of its simplicity. What I also found interesting about the design were cork finish of DAC's feet – no rubber, plastic, no spikes, just metal feet with cork washers. Obviously cork was a choice not a must, and I can only assume that it was carefully made to improve sonic and not the other way around. Femto sports all sorts of digital inputs: 2 x coaxial, 2 x AES/EBU, 2 x Toslink, BNC and USB, all of them accept a signal up to 192kHz, and analogue outputs, both balanced and unbalanced. It looks like guys from Calyx had seen some Modwright devices and decided a very simple bu t clever solution – each sockets has a double description – one above it, let’s say a 'regular' one, and one below, that is turned upside down so you can easily ready it when bending over the device to plug in some cables (which is a case for at least 90% of users I assume). There is a very nice, large, easy to read display on the front, and 7 push-buttons next to it, that allow you to control the device. This above average sized display shows a lot of data like: input, sampling frequency of the signal, setting of a digital filter, phase, and, of course, volume level. There is also a remote control attached – nicely machined from aluminum (not some cheap, plastic one) that sports exactly the same 7 buttons, in exactly the same array as the front panel of Femto. That really makes thing easier for user. The on/off button sits on a side wall of the device which makes it no so easy to track when you use a device for the first time. When I saw the quality of Femto's finished it only confirmed what I already knew – if you want a solid, great looking casing for your device you should look for a manufacturer in South Korea – they are really good at it. Calyx DAC 24/192 was one prove, Eximus DP-1 the second, and now Femto confirming it one more time – solid and great looking at the same time.

The name of this DAC – Femto – comes from a femtosecond, which is the unit of time equal to 10−15 of a second. These are the unit used to measure a jitter of this D/A converter, which according to the manufacturer is the lowest that any device on the market has to offer. Most competitors measure a jitter of their products in picoseconds (10−12 s). Of course it is debatable whether a human ears can really catch a difference, but on the other hand human ear is able to pick up some things that it hypothetically isn't supposed to. So if Calyx is able to provide us with a device with the jitter measured in femtoseconds, why the hell not?
As I already mentioned Femto sports a digital volume control that works in 0,5dB steps from 0 (total silence) to 100 (0 dB), and that allows user to drive an amplifier directly with it. When used with a preamplifier volume should be set to the maximum which allows to bypass the digital volume control. 24/192 DAC used an ESS Technology ES9018 Sabre chip and Femto uses exactly the same one, but two pieces of them, one for each channel. The USB input works, of course, in an asynchronous mode, and its based around XMOS chip. As usually Apple computers need no drivers to work with Femto, and PC owners have to download and install proper driver. Installation on my AudioPC went smooth even though I have a 64-bit Win8 installed (which creates problems with many different drivers) with JRiver 18 and Jplay.


Recordings used during test (a selection)

  • Bobo Stenson Trio, Indicum, ECM, B008U0FJ9Y, FLAC.
  • Arne Domnerus, Jazz at the Pawnshop, FIM XRCD 012-013, CD/FLAC.
  • Ella Fitzgerald & Louis Armstrong, Ella and Louis, Verve/Lasting Impression Music, LIM UHD 045, CD.
  • The Persuasions, A capella dreams, Chesky Records, B0000D9PHK, CD/FLAC.
  • AC/DC, Back in black, SONY, B000089RV6, CD/FLAC.
  • Tsuyoshi Yamamoto Trio, Autumn in Seattle, FIM XRCD 043, CD/FLAC.
  • Hanna Banaszak, Live, Polskie Radio, 5907812243944 , CD/FLAC.
  • Keith Jarrett, The Köln Concert, ECM/Universal Music Japan, UCCE-9011, CD/FLAC.
  • Rodrigo y Gabriela, 11:11, EMI Music Poland, 5651702, CD/FLAC.
  • Led Zeppelin, Led Zeppelin, Atlantic/Warner Music, WPCR-11611, CD/FLAC.
  • Beethoven, Symphonie No. 9, Deutsche Gramophone, DG, 445 503-2, CD/FLAC.
  • Muddy Waters & The Rolling Stones, Live At The Checkerboard Lounge, Chicago 1981, Eagle Rock Entertainment, B0085KGHI6, CD/FLAC.
  • V.A. Mozart, Le Nozze di Figaro, Harmonia Mundi HMC 901818.20, CD/FLAC.
  • Pink Floyd, Wish you were here, EMI Records Japan, TOCP-53808, CD/FLAC.

Even though the distributor informed me that this particular unit was already fully broken in I still gave it 2 full days for a warm up in my system before I started my listening sessions. This test preceded the one of Accustic Arts, and so I did not have this high quality CD Transport by AA at my disposal at the time. But to be honest I was primarily interested in USB input's performance. Also I knew that Femto would get its chance to shine in a full Reymio system, fed with signal from one of the best transports available.

Femto po USB

I started my audition with Femto acting as a D/A converter only, with my AudioPC as a source, Modwright LS100 + KWA100SE setup amplifying signal, and with fabulous Ardento Alter, that I received again for auditions in a slightly modified version. Why did I go with computer first? Because, as already explained, I remembered very well a great performance of 24/192 DAC and I assumed that in Femto case also an USB input might be superior. Also, to be completely honest, there is plenty of DACs that offer great performance when fed via coaxial input, but quite a few that can offer similar, or better performance when signal is delivered via USB. Calyx had already made a name for itself of a company offering great USB converters so I counted on it.

The first note I took during first listening session was, I quote: 'amazingly musical performer'. This Korean DAC surely belongs to this category of devices that don't allow listener to focus on sound analysis. Its performance immediately attracts listener's attention, involves him in the amazingly colorful world of music. In my case the first recording, that impressed me so much was fantastic (for both, technical quality and music) recording from ECM label – a Bob Stenson Trio Indicum, played from 24/48 FLAC files. When I played it for the first time I managed to focus on task – which was supposed to be Femto's assessment – for like 5 seconds, because right after that the world created by musicians and reproduced so well by a system with Femto in it, swallowed me and I forgot about basicaly everything, not just the assessment. So I had to play it for the second time to write anything else apart from: 'fantastic, brilliant, amazing' and so on. What attracted attention most was beautiful, rich, vast in volume, magic and magnetic piano – as I see it now at least equally great as the one delivered from a CD by Accustic Arts source (with Transport hooked up to the DAC with coaxial cable). But of course it wasn't a solo piano recording. There was also very impressive percussion – each time a stick hit one of the cymbals the sound was not only very immediate, not only amazingly vibrant, but also delivered with even tiniest details regardless of drums being only a support instrument placed in the back of the stage. And finally my favorite instrument – the bass, also rather supporting piano in this recording rather than taking lead, but still very rich, colorful, dynamic, with lots of wood and long, wonderful decay. Spacing was also great – very plausible, 3-dimensional with each instrument precisely placed on the stage and recreated as a 3D source of sound, not just a point in space. Also the space between instruments was filled with air that allowed each of them to breathe. And finally this device allows listener to get really deep into the music and its ambiance, to feel its heart and soul which is a breathtaking experience that simply doesn't leave any space for anything else but music, or in other words it makes everything but the music irrelevant.

All the next jazz recordings only confirmed what I already observed, proving also that Calyx is fully capable of rendering any and every well recorded instrument delivering very convincing, life-like sound. I played some recordings with a trumpet, saxophone, clarinet and vibes and each time there it was – the 'wow!' effect, as I was amazed with the way Femto beautifully rendered each of them in the space, how plausible these instruments seemed in my room. These recordings presented also clearly other strong virtues of Korean DAC – extraordinary resolution and selectivity. With bands bigger than trios, the 'wow!' effect was still there regardless if I was following the big picture or even the smallest details, nuances usually hidden somewhere in the back of the mix. To be honest during listening sessions with Femto I acted a lot like a kid in a toy shop – look Mom this toy is the best, no the other one is better, or wait there is a next one and it beats all, and so on, and so on. I was in fact cruising across my music files directory just wondering and then checking how particular piece, or sometimes just a single instrument would sound played via Femto. And even though my expectations grew with every recording, this fabulous DAC kept satisfying them. So I kept challenging it again and again and... finally I had to stop, as the time of each review is somehow limited, unfortunately.

It was time to check how well could Femto deal with other music genres. So I moved from acoustic jazz to vocal recordings. I started with The Persuasions and their Acapella dreams (24/96 files) – the purest form of vocal, a capella. Once more did Calyx fulfill its job amazingly well delivering voices in the most convincing, involving way. The already mentioned great selectivity allowed me to follow any chosen voice, to study its texture, timbre, all the details that differentiated this particular voice from others.

Presentation was also so palpable that I 'saw' these five guys standing maybe 3 meters away from me. Voice was coming not only from a proper horizontal placement of each guy, but also from a proper height. I could 'see' them moving to the rhythm of their singing, making faces and so on – it was one of the closest experiences to the ones from live concerts.

Moving to a much more dynamic music, like some AC/DC recording did not impress Calyx much – it was clearly not afraid of a need to 'make some noise'. There was rhythm, timing, bass extension and extraordinary differentiation, hefty, clear and vibrant treble, and quite a lush and smooth midrange with a very good resolution, that allowed Brian Johnson's vocal to be heard and, what's more difficult, to be understood. Femto seemed also to be able to deliver almost overwhelming energy produced by Angus Young and his crew. The Metallica's black album proved that proper kick of a rich, deep bass wasn't a problem to reproduce, and neither was a bit harsh, powerful but very fluent sound of electric guitars and equally rough voice of one James Hatfield. I have to admit that I liked this presentation a lot also because Calyx delivered bass the way I liked it which was a perfect match for my Modwright + Ardento setup – bass was very well extended, had a good grip, it was rich, there was impressive differentiation, proper weight and power and all these elements were key ones for Femto's presentation, and not a supersonic speed, or some extreme tautness that were priorities for some other DACs.
Another very energetic experience was a listening session with a 'new' hi-res files of Michael Jackson's Thriller. This album played from a CD could not compare in any aspect with fantastic performance of a vinyl edition. CD lacked the timing, and power of a record, and only the latter provided truly impressive pace&rhythm. But the hi-res version from HDTracks proved that a digital copy of this great album could also sound amazingly well, at least as well as the black record did. Under one condition, of course – the rest of the system has to be able to keep the pace with this recording. My system, with Femto as a source, did, in my opinion, fabulous job. I was totally blown away while listening to Beat it, or Billie Jean, and the volume knob wondered to the area it never went before. I knew my neighbors would hate me but at the moment I didn't care, I couldn't resist this pure joy and great entertainment that Calyx offered.

Femto didn't let me down also when playing some classical music like my favorite Beethoven’s 9th Symphony conducted by Boehm, which truly benefited of all key features of Calyx's sound – great resolution and selectivity, liquidity of the sound and the overall musicality of its presentation. I use this particular performance often as a test of how well the particular device can differentiate dynamics, how it deals with sound going suddenly from pianissimo to fortissimo which provides a lot of information on dynamics in both micro and macro scale. Considering how well this test was going so far I kind of hoped that I would finally find at least some scratch on the surface of so far 'perfect' sounding device. But I didn't find any – I just sat there, on my couch, totally enchanted, listening to a presentation that was more engaging than any other I had heard before.

The easiest summary of Femto's USB performance would be as simple as that: Femto is the best USB DAC I heard so far, period! Already 24/192 DAC was something special considering its USB performance, but Femto goes easy beyond that with much more refined, sophisticated sound. It achieved a level of performance comparable with what amazing Accustic Arts TUBE-DAC II MK2 presented together with dedicated CD transport hooked up with BNC cable. Obvious advantage of the Korean device is its ability to play hi-res files, that sound better than 'regular', 16/44 ones. Personally I'm not one of these people who claim that there is a gigantic quality difference between 16/44 and 24/192 files, but still I admit there is a difference to the favor of hi-res files, only it's not as huge as many people claim, and Femto clearly shows that difference – 24 bits mean in practice 'more music in music'. The presentation seems denser, has more weight to it, its more tuneful, easier to absorb as it sound more natural. In my opinion Femto proved that the more important part of the equation are bits and not sampling frequency which was clear to me when I listened to Bobo Stenson Trio played from 24/48 files. Anyway – if you're looking for the top USB performer for your system, Femto is a must on your 'for audition' list.

Femto as a preamplifier

I shall not elaborate much on that topic, as although Calyx did its job of driving Modwright's power amp pretty well, but the system as a whole sounded far better with LS100 preamplifier in the system. Femto, you might say, drives amp just fine, and it's hard to point out any downsides, but all I had to do was to set its volume to the maximum (to bypass its volume control) and hook up LA100 to hear the difference. Sound was now richer, smoother, more colorful, and the only aspect I thought might not had improved was transparency. Obviously LS100, although not too pricey, offers fantastic price/value performance and, in my opinion of course, it is hard to find a better tube preamplifier even at twice the price. Plus of course it works with same manufacturer's power amp damn well. So these two fact make it really tough for any device with volume control to beat LS100+KWA100SE combination. Don't get me wrong – Femto's volume control is pretty good, so if you want as simple system as possible, you can surely use it to drive power amp (assuming you don't have any analogue source of course) and you'll be fine. What you need to know is that a high quality preamplifier will allow you to hear even more of the great potential of Korean D/A converter. In one of the reviews the owner of Calyx admitted that they were working on a preamplifier themselves, so (that's of course only my presumption!) they might have come to the same conclusion as I did – to show the full potential of this outstanding device one should use even better volume control than the digital one implemented in it.

Femto via coaxial input

As I already mentioned I do not own any highest quality CD transport myself, nor I had any at my disposal at the time of this test, so I couldn't really expect to explore the limits of a coaxial input's performance, ergo achieve as great performance as from USB input. Indeed, sound was bit less liquid, not so amazingly rich, I lacked a bit of this fantastic differentiation I had heard before, and the soundstage wasn't so incredibly palpable as before. Again – don't get me wrong, this was still a very good performance but not so impressive after what I heard before from USB input. Yes, via USB I could play hi-res files, which made a difference, but I also played 'regular' CD rips, so 16/44 and these still sounded better, than CD themselves played via coaxial input. Also, even though it happened bit later, Accustic Arts setup (CD transport + D/A converter) proved that CD might still sound damn well, incredibly well even. Hell, even German DAC with the very same Oppo (that I used with Femto) as transport sounded bit better than with Korean device. So I had two choices – either to draw a conclusion that Femto's, just as 24/192 DAC's before, USB input simply outperformed coaxial input, or I could still give it a chance with some top quality CD transport. I chose the latter. Unfortunately Calyx and fabulous Accustic Arts Drive II did not meet under my roof, so I did the same thing, as already couple of times before – I called some friends and we met at Jacek's place to test Calyx in a Reymio system, that included a CDT-777 CD Transport – one of the best I knew. Femto settled in this Japanese system (a system that doesn't like 'strangers' much) really nicely. Soon we started even to poke our host gently suggesting that he could consider replacing his Reymio D/A converter for Femto because it sounded so good. With CDT-777 Femto delivered amazingly smooth, liquid, rich and palpable sound, which reminded me very much what I had heard before using AudioPC as transport via USB input. It seemed now, that with top quality CD Transport Femto was able to deliver sound with the same, or at least very similar qualities, as when fed via USB. We couldn't experience head to head comparison as Jacek (at the time) didn't use any computer as a source in his system, but in my ears it felt at least close enough to acknowledge that Calyx did a great job and this time offered a device capable of delivering top performance not only from USB input. All you need is a top performance CD Transport.
Obviously considering both the price of Femto and the number of digital inputs one would rather consider it obvious, that the Korean manufacturer wouldn't charge customers that much just for a great USB performance. I still believe that the best, most complete, mature sound you get from Femto comes from USB input, but I have to admit that with proper transport you can get almost the same level of performance from other inputs. And don't let this 'almost' mislead you – that is still a top performance that many other D/A converters, even some more expensive ones, are not able to match. It seems that whatever input should you use an amazingly musical, involving, precise, and detailed sound is what you'll get. I believe that it is a USB input that can get you absolutely top performance of this DAC, but the other inputs are just a half step behind if you provide a high quality source. This device will fit even into most high-end systems, even though it doesn't cost as much, as many other high-end D/A converters. Way to go Calyx! You did a fabulous job – it's the best USB DAC I heard so far, but also one of the best ones all together.


Calyx Femto is a digital-to-analogue converter with digital volume control. Unlike its predecessor, 24/192 DAC, it is much bigger, and better equipped device. The design will impress most audiophiles from the very first look, as it sports a very solid, simple but elegant, aluminum casing, available in silver or black. It sits on metal feet finished with cork, that according to the designer did its job better than other material. Front sports a nice, large display, that makes reading any information displayed on it easy, even from a distance of a few meters. On its right side there are 7 push-buttons that allow to control the device. Femto comes also with a very nice, handy, aluminum remote control that sports exactly the same 7 buttons in exactly the same array as on the front panel The main on/off switch sits on the side wall of the device. The back sports a large array of 8 (!) digital inputs, that include: 2 x coax, 2 x AES/EBU, 2 x Toslink, 1 x BNC, 1 x USB, and analogue outputs, both balanced (XLR) and unbalanced (RCA).
It's a dual-mono design, with separate 32-bit, 4-channel ESS9018 Sabre DAC chip for each channel, each of them being equipped also with a separate, ultra-precise, ultra-low jitter oscillator with jitter measured in femtoseconds – it measures (according to the manufacturer) 500 femtoseconds (which is a 0,5 picosecond). Now the name of this device should be self-explanatory. Not only both channels have their own oscillators, also the USB input has its own. Each of those oscillators is shielded in a metal casing. Femto employs two separate power supplies, one for the digital circuits and the other for the analog output stage and each of them is also shielded in a separate metal casing to separate them from electronic circuits.
USB input uses XMOS chip set, which operates asynchronously. Mac users don't need any additional drivers to start using this DAC, those with Windows operated Pcs have to install a driver that is available on manufacturer's website. I had no problem installing it on my WIN8, 64-bit system.

Specification (according to Manufacturer)

  • Digital inputs: Two Coaxial / Two Optical / Two AES-EBU / BNC / USB
  • Sampling rate: 44.1kHz ~ 192kHz
  • Frequency Response: 20Hz ~ 32kHz @ - 0.5dB - Balanced Output / 20Hz ~ 38kHz @ - 0.25dB - Unbalanced Output
  • Total Harmonic Response: Less than 0.0003% @ 1KHz, 0dB - Balanced Output & Unbalanced Output
  • Signal-To-Noise Ratio: 130 dB, A-weighted - Balanced Output / 124 dB, A-weighted - Unbalanced Output
  • Dynamic Range: 130 dB, A-weighted - Balanced Output / 124 dB, A-weighted - Unbalanced Output
  • Channel Separation: 144 dB @ 1KHz, 126 dB @ 20KHz - Balanced Output, 140 dB @ 1KHz, 124 dB @ 20KHz - Unbalanced Output
  • Output Voltage: 6.8 Vrms - Balanced Output / 2 Vrms - Unbalanced Output
  • Output Level Control: - ∞ ~ 0 dB, 0.5 dB Step
  • RMS Jitter: 500 Femtoseconds
  • Dimensions: 430mm x 102mm x 403,8mm (W x H x D)
  • Weight: 18,5Kg