List Price: $6,850


Review by

Malcolm Gomes


Few will argue that the hottest category in high-end audio today is the digital to analog converter. Most of the established brands have got into this segment and competition is not just fierce, but it continues to heat up with new entrants regularly entering the fray with their own DACs.


This fierce completion has been good for consumers as, with each passing year we have seen SOTA technology not just advance, but also trickle down from the top-of-the-line models to the more affordable models. This means that, provided you do proper due diligence, your DAC dollars buy better performance than it did in the past, giving you better value for money than ever before.


The buzzword in the world of DACs for the past decade has undoubtedly been ‘jitter’, which simply put, is the timing error in the digital stream of ones and zeros before the signal is converted from digital to analog. Everything else being equal, the DACs with lower jitter tend to sound better. Thanks to technology advances over the past few years, the better DACs have been able to reduce jitter to a few hundred pico seconds.  When you consider that a pico second is one trillionth of a second, a DAC with jitter of a few hundred pico seconds would seem to be pretty good stuff. However, human hearing is so incredibly sensitive, many of us can still hear and be bothered by jitter measuring a few hundred pico seconds.


This being the case, I was thrilled to learn that Dr. Seungmok Yi, the founder of Digital and Analog, made a breakthrough in jitter reduction and would soon release a DAC under the Calyx brand, with jitter so low, it has to be measured in femto seconds, which is one quadrillionth of a second.   


To help you get a more real world understanding of these units of measure, let me put it in another way: The difference between a picosecond and a regular second is the difference between one regular second and 31,700 years. If you think that is huge, then consider this; the difference between one femtosecond and a regular second is the difference between one regular second and 31.7 million years.

So what does a DAC with less than a pico second (500 femto seconds) of jitter, sound like? That is what I was really keen to find out and so I made sure I got my hands on one of the first production units of the ‘Femto DAC’ to roll out of Calyx.

The first thing that struck me about the Femto DAC was the build quality and the weight (40.5 pounds).  Built like a Victoria’s Secret model driving a tank (I’ll pause for moment so you can capture that visual) it has a case of solid billet aluminum with a sleek, sophisticated design that oozes understated elegance. The other thing that struck me is the size. The Femto is, by far, the largest DACs I have reviewed.  It is 430 mm wide, 102 mm high and 403.8 mm deep. Supporting this hulk DAC are four cork feet, which is quite unusual given that many high-end DAC have chosen to go with feet made out of rubber compounds. According to Calyx, they found that cork enhanced the performance of the unit.

The over-the-top build quality extended to the interior where I found very high quality components including the venerable Sabre ESS9018 patented 32-bit Hyperstream chips, which have 8 converters per channel and are considered by many to be state-of-the-art.  Although the ESS Sabre chip is capable of processing DSD, Dr. Yi decided not to avail of this option so you will not find a DSD input on the Femto DAC. Dr.Yi’s rationale for this omission is that he believes that the DSD signal is susceptible to jitter and external EMI. He also argues that there is still no universally accepted standard format to transfer a DSD signal.



The Femto employs two separate power supplies, one for the digital circuits and the other for the analog output stage. To ensure minimum interference between circuits, Dr. Yi has again gone the extra mile and enclosed each power supply in its own metal-shielded casing. The oscillators in the Femto DAC have multiple PLL to minimize RMS jitter. The Femto DAC design does not utilize any wiring in the signal path, as Dr.Yi believes this to be the better way to go for superior performance. According to him, the Femto DACs are made one at a time and after each one is assembled, it undergoes 3 hours of testing before it is packed for shipping. He recommends at least 100 hours of break in time although he feels that the unit sounds great right out of the box.

All this incredible attention to detail results in a DAC that delivers remarkably low total harmonic distortion, which measure at just 0.0003% @ 1 kHz. The frequency response is equally impressive at 20Hz to 32 kHz @ -0.5dB, as are the signal to noise ratio and dynamic range both of which measure at an impressive 130 dB. The dual mono design results in channel separation that is all the way up to 144 dB which some DACs, even at double the price, cannot match. Unlike some DACs in its price range, the Femto DAC adopts the purist approach, eschewing any form of up sampling or oversampling during the processing of the digital signal.

When I asked Dr. Yi if we could expect a DAC from Calyx that would handle music files with a resolution higher than 24/192, he opined that the market did not need it as 32-bit music files are way too large and are virtually non existent at the consumer level, a situation, he does not expect to change in the foreseeable future, which is exactly what our Publisher has said previously. Yi also pointed out that higher resolution than 24/192 would need a more accurate clock that will drive up costs quite exponentially. Having said that, the SPDIF input of the Femto DAC is capable of handling 32-bit signals but the USB is restricted to 24-bit because of the limited capability of the X-MOS chip.

In terms of digital connectivity, the Femto DAC is hard to beat. It offers a plethora of digital inputs including two coaxial, two AES/EBU, one BNC, two optical and one USB. On the analog output front, it offers a pair of RCA as well as a pair of balanced outputs. I find it hard to imagine a scenario where you would need more connectivity than this.

The Femto DAC come with an elegant full function, all metal remote control that is solid enough to match the look and feel of the DAC. Drop it on your toes and you are quite likely to need some medical attention.

The DAC does offer a built-in, high-caliber pre amplifier, complete with a high quality 32-bit digital volume control that eliminate the need for a separate pre amplifier that allows connection directly to a power amplifier. You can adjust the volume level from zero (mute) to 100 (0 dB) in 0.5 dB steps.

I was told that, when using the Femto DAC with a preamplifier, the volume level should be set at 100, which lets you bypass the unit’s own preamplifier. I tried the Femto using its own preamplifier with an external preamplifier. Although the internal preamplifier is extremely capable, I was able to get better results using a high quality external preamplifier, so the remainder of the review was done in this configuration.

The only thing that came out of the carton that I found wanting is the Femto DAC Instruction Manual. This is a bare bones document that gives only the most basic information about the product, although it does offer quite a few charts on various performance aspects of the product.

One design feature of the Femto DAC that I did not care for is that the power on/off button is on the side of the DAC rather than the front. According to Dr. Yi, the power button was placed at the side for aesthetic reasons. I would have preferred to have it on the front where it would be more accessible, but obviously that has nothing to do with the sound quality.

To set up for the audition I connected various sources to the Femto. I hooked the Bryston BCD-1 and the BDP-1 via the AES/EBU inputs.  The Sooloos got one of the Co-axial inputs and my iMac fed it via the USB input. I tried out the DAC with and without a pre amp (Bryston BP26) and with a tube (Ars Sonum Filarmonia) and a solid-state amp (Ayre V3). The speakers used were the Merlin VSM Masters with the Master BAM and RCs, which were connected using Cardas Clear Beyond speaker cables which Stereomojo reviewed recently and are the recipient of our Best of 2011 Award.. The digital and analog interconnects were Cardas Clear.

Dr. Yi told me that the Femto DAC needs good cables to optimize its performance. He opined, and I agree with him, that it is very important to ensure that the cables deliver accurate impedance. Like him, I could easily tell the difference that good cables made. According to Dr. Yi, most cables from reputed brands are well made, although he has encountered some very pricey cables that are so poorly made, they do not deliver accurate impedance, thus adversely affecting the sonic performance. His advice is to test cables before you buy them.

I allowed the Femto DAC to burn in for 180 hours before I began the review. You would be amazed at how many reviewers don’t take the time to properly burn-in review products, even though the designers state that it is necessary for optimum performance.

The music albums I chose for the audition were the ones that I had on CD, in high-rez files on a hard drive on my Sooloos and on my iMac. These included The Definitive Simon & Garfunkle, Boz Scaggs - Dig, Cantate Domino (Oscar’s Motet Choir), Eva Cassidy – Somewhere and Jazz at the Pawnshop. I began with the CDs before moving on to the Sooloos, the digital player and then the iMac.

Right out of the gate, what jumped out at me was the incredible focus with which the Femto DAC locked in the sonic image. The sound stage was enormous; the air around and between the instruments was closer to a live performance than most of other DACs that I auditioned before at the same price point. Tonality was spot on as was the speed and rhythmic timing. Also obvious was the incredibly low noise floor that allowed even very subtle micro details and nuances in the music to show through without having to strain to listen to them.

Even challenging transients were executed with uncommon ease and the softer instruments like the flute and oboe were rendered with the fragile delicateness they possess, which added greatly to the listening enjoyment. Bass was deep, tight, authoritative and well controlled. However if you are looking for that artificial explosive bass impact that you can feel on your chest, which hardly ever occurs at acoustic live performances, the Femto DAC is not going to give it to you.    

What also struck me was that, besides revealing very minute details in the music, there was also a distinct lack of digital artifacts. I could hardly detect any glare or hard edges to the music. In fact I was struck as to how close to analog the sound was. I should say that I have always had a very strong bias towards analog (vinyl) music reproduction.

Vocals, especially female, came through with eerie presence and with a lot more texture and body than I am used to hearing even through stratospheric priced DACs. The emotion that came through when listening to Eva Cassidy’s “Blue Eyes Crying in the Rain” gave me goose bumps. Dynamic contrast came through in spades. Even at very low volume I could hear micro details that usually disappear at this level. When playing certain complex tracks with a lot going on in the music, at very high SPL, I could detect a very slight hint of smearing.

Reproducing choir performances is always challenging. Many DACs reproduce them as a blended whole. The Femto DAC was different. Listening to the Oscar Motet Choir’s rendition of “Advent” was a revelation. The various voices were rendered like the separate entities they are but harmonizing beautifully together, which is closer to what you hear when you listen to a choir performing live.

The only time I have enjoyed listening to Simon and Garfunkel more than this was on very high-end vinyl equipment. At this level, you really appreciate the incredibly synergistic harmonies of this talented duo. I can’t remember when I enjoyed the classic “Mrs. Robinson” more via a digital source. There were also many tracks on other albums where, for the first time, I heard a much softer second voice gently harmonizing with the main voice. Hitherto, all I heard was the main voice.

Jazz  at the Pawn Shop is generally acknowledged as one of the best recordings ever made. Through the Femto DAC, it is easy to see why. What came through was not just great articulation of each and every instrument on this album, but the subtle spatial cues which allowed me to suspend disbelief and imagine that I was at the recording venue, enjoying the ambience of being surrounded by diners enjoying their meals and drinks while waiters scurry between the tables serving them. Before, very few DACs allowed me to sense the acoustics of this performance venue so accurately. I particularly enjoyed listening to “High Life” and “Limehouse Blues” where Arne Domnerus’ performance on the alto sax and clarinet sounded so real, they made me want to order a JD and Coke.


The front to back, side-to-side and top to bottom sonic image was so holographic it was as much a visual experience as a sonic event. The sound also had the kind of liquidity that enchants the listener and helps connect emotionally with the performer.

The amazing accuracy with which the Femto DAC reproduced the recordings was a double-edged sword. It made good recordings sound truly glorious, but it ruthlessly revealed flaws in bad recordings. It was also not so forgiving with lower resolution digital files. Audio files 320 kbps or higher sounded great. The files with 256 kbps still sounded reasonably good, but files with lower kbps were revealed for their threadbare character.  

The Femto DAC offers three filters that offer different LPF in the digital domain at 50kHz, 60kHz and 70kHz. Although the differences were very subtle, I preferred Filter 1 and auditioned the DAC on this setting.

Given the ease and effortlessness with which the Femto DAC delivers music, I decided to test out its fatigue factor. I invited a few audiophile friends over during the weekend and we began a listening session at around noon and, except for a lunch and dinner break, we stretched it out well into the wee hours of the next morning. Amazingly, we found ourselves still wanting more. That says a lot for how fatigue free the Femto DAC is. It also says a lot about the progress of digital playback in general.

Unlike its smaller and more affordable sibling the 24/192, where the USB input clearly outperformed the SPDIF input, with the Femto you get great sound irrespective of which input you use. The USB still had a slight edge over the others, followed by the AES/EBU, the BNC and the Coaxial. The optical input, while still pretty good, was not in the same league as the other inputs. Dr. Yi is in the camp that believes that USB 2.0 is fast enough and so there is no added advantage to using some of the new, faster interfaces like USB 3.0 and Thunderbolt. Dr. Yi’s preferred source for the Femto DAC is a "very silent computer".

In terms of outputs, the XLR fully balanced outputs had a small but significant advantage over single ended RCA outputs, offering more full-bodied sound with a blacker background.

As I mentioned before, using good digital and analog interconnects made a significant difference to the performance of the Femto DAC. As part of the review I exchanged the Cardas Clear for lesser quality interconnects and it was easy to tell the difference.  

At $6,850, the Femto is hardly a cheap DAC, so is it worth the money? From the overall performance point of view, it is definitely not embarrassed by most of the solid state DACs at the same price point and better than a few of them in certain areas.  When it comes to build quality and connectivity, it blows away most of the completion. One area where it lags some of the other DACs in its price range is in brand recognition. Calyx does not have the same brand recognition and image as Berkeley, Wavelength, DCS or Weiss, to name a few. Of course, name recognition comes from what, dear reader? Advertising. Advertising in this business begats reviews. Pay enough, you get on the cover of magazines. Ever seen a bad review of a stereo product on the cover of a magazine? However, if Calyx continues developing products with the quality and performance level of the Femto DAC, it’s only a matter of time before it, too, becomes an aspirational brand because of owner word of mouth.

Compared to the Invicta, which I reviewed for Stereomojo, the Femto DAC has comparable build quality but more connectivity. It also has an edge in performance especially via USB. The advantage that the Invicta has over the Femto DAC is the SD Card reader capability, a digital-out option, an HDMI interface and headphone capability, which Invicta has implemented very well. On the flip side, the Femto DAC’s remote control is a classy, elegant, solid metal component with full functionality. In contrast the Invicta has a plastic remote with limited functionality. But, the Femto is close to double the price of the Invicta and that would compel me to give the Invicta a slight edge in terms of value-for-money.

I also compared the Femto DAC to the Bryston BDA-1, which at $1,995 is less than one third the cost. We reviewed it when it came out a few years ago. The only area where the The BDA-1 could approach the Femto DAC is in connectivity. In terms of performance and build quality, the Femto is streets ahead even when connected to Bryston’s own BCD-1 and BDP-1. Justifiably, a lot has been made of the outstanding synergy between the BDP-1 and the BDA-1, but when I connected the BDP-1 to the Femto DAC, performance reached a whole new level. The BDA-1 is a very good DAC and the BCD-1 is a superb CD player, but the Femto truly revealed the heights that these two components can reach if connected to a great DAC.


Three of the very highly regarded solid-state DACs today, which are in the same price range as the Femto DAC, are the Berkeley Alpha DAC Series 2, the Weiss DAC 202 and the dCS Debussy. The Berkeley Alpha DAC series 2 sells for $4,995, the Weiss DAC 202 retails at $6,670 and the dCS Debussy can be had for $10,999.

When comparing the Femto DAC to these three stalwarts, you have to keep in mind that, while the dCS offers a USB input, the Berkeley and the Weiss do not and you need to invest in a good USB to SPDIF converters to enjoy music via USB. This adds around $1,500 to $1,800 to the price, which would bring the Berkeley to around the same price bracket as the Femto DAC and puts the Weiss at more than a grand over the Femto price.

In terms of overall sonic performance, I found the Femto DAC to be in the same league as these highly regarded DACs. However, each of the four DACs has their own strengths and weaknesses. In comparison to the Debussy, the Femto is not nearly as adept at retrieval of micro details. In this regard the Debussy is not unlike an electron microscope. It has few rivals at revealing ‘everything’ in a recording to deliver the best resolution of all the DACs that I have heard.

For short term listening, you’ll be hard pressed to find a DAC that will satisfy you more than the Debussy. Ironically, the trade-off is that it is too much of a good thing and listener fatigue can set in during very long listening sessions. In contrast, the Femto DAC may not have the extreme detail retrieval of the Debussy, but thanks to the ease and effortlessness with which the Femto DAC delivers music, you can listen for hours with negligible listener fatigue.

The Femto DAC is a lot closer to the sound of the DAC202 than to the Debussy. Both the Femto DAC and DAC202 deliver sound that is full bodied, smooth and very organic. The DAC202 has a slight edge in delivering the higher frequencies, which it does with a more delicate touch than the Femto DAC. There is not much to choose between the two when it comes to mid range performance but the Femto DAC definitely has the upper hand in bass reproduction, especially in the two bottom octaves. The bass reproduction of the Femto DAC is tighter and more tuneful than the DAC202. The differences are not huge, but at the same time, not so difficult to detect.




In comparing the Femto DAC to the Alpha DAC Series 2, both do an incredible job communicating the emotions in the music. I experienced ample goose-bump moments while listening to both. While listening to the Alpha DAC Series 2, I did detect a more pronounced bloom and a captivatingly sweet treble, which while not necessarily always true to the recording, is very seductive indeed!

The sound stage created by the Femto is a smidgen more solid and forward. In comparison, the Alpha DAC Series 2 is a bit laid back. Both DACs are great at reproducing bass. However, there are subtle differences. The Alpha DAC Series 2 delivers bass that could be described as warm and full, while the Femto DAC’s bass is tighter, deeper and ever so slightly more tuneful.

If you use live music as a reference, to my ears, the Femto DAC is closer, in that it was easier to suspend disbelief and imagine that you were in the presence of a live performance. The Alpha DAC Series 2 is more forgiving of less than stellar recordings than the Femto DAC, which mercilessly revealed recording flaws.

If I were to allocate human personalities to these two DACs, I would describe the Alpha Series 2 as the sweet talker and the Femto as the straight talker. I guess the only really dramatic difference between the two is their physical weight. If they were boxers, the Alpha Series 2 at nine pounds, would probably be classified as a welterweight, whereas the 40.5-pound Femto would undoubtedly belong with the heavyweights.


Unlike the Femto, the Alpha Series 2 and the DAC202 offer the option of detecting, whether or not the signal received by the DAC is a bit perfect version of the original data stream. In addition, the DAC202 also offers the option of a firewire connection, which is technically superior to USB 2.0 and so may be tempting if you own an iMac. On the flip side, the Femto DAC is USB compatible whereas the Berkeley and DAC202 are not.

Berkeley believes that to obtain the best USB performance, it is important to house the USB to SPDIF circuitry in a separate chassis. After auditioning the Invicta and especially after reviewing the Femto, I now find that argument harder to accept. Both the Invicta and the Femto DACs have implemented their USB solution in a single chassis well enough to convince me that a separate chassis for the USB to SPDIF conversion does not necessarily or automatically hold a performance advantage.

Given how well the Femto is designed and built, I just had to find out more about Seungmok Yi, the man behind Digital & Analog Co., Ltd. and the designer of the Calyx Femto DAC. I wanted to know what motivates him to strive for perfection with such passion. What I learnt is that Dr. Yi loves attending live concerts and has made it a point to attend them very frequently. Now that explains a lot. As most people who frequent concerts (myself included) realize, there are few pleasures on earth that can match the sonic majesty of a live concert performed by talented musicians at a venue that has superior acoustics.

Frequenting live concerts also give you a great mental reference of what live music really sounds like. It makes you realize that even state-of-the-art high-end audio systems still have some way to go to emulate the true majesty of a live musical performance. The quest to design products that bring reproduced music as close as possible to the live event is what drives Dr. Yi to go to great lengths to get each and every detail right irrespective of how long it takes or how much it costs in R & D. Academically, Dr. Yi majored in two areas, namely math and physics, which he feels gives him a very good understanding of audio circuitry. In 1991, he did his Ph.D. in math at The State University of New York at Stony Brook.


Dr. Yi got his first audio system in 1983 and it included a Garrard Zero-100 turntable, a Kenwood receiver and an AR 100 which were gifted to him by a friend as a token of his thanks to Dr. Yi for introducing him to the world of live classical music. Fast forward to 1993 when Dr. Yi joined ‘Hifinet’, a distributor for high-end audio brands in South Korea. A couple of years later he started a distribution company to import high-end audio brands there. Then in 1999 he established a company to manufacture class D integrated circuits and analog to PWM modulator ICs. To help get this venture off the ground, he put together a team of the best engineers he could find in South Korea.  This Company was so successful, it became a supplier of OEM parts to the top electronic companies in Korea, including Samsung Electronics and Daewoo Audio Technologies. The emphasis at the time was in mass production, but the music lover in Yi soon started getting the urge to design and manufacture affordable audio systems that would enable the man on the street to enjoy great sound that approaches the live performance.

His first foray into this field was to design audio systems using class-D circuits, which would deliver great sound for the price. He marketed these under the Calyx brand and the rest, as they say, is history.

After experiencing the impressive performance of the Femto DAC, I was curious to know more about Dr. Yi’s design philosophy. That proved to be quite straightforward. Rather than try and voice a product, Dr. Yi focuses on doing everything possible to reduce or eliminate noise.  He points out that many people are unable to differentiate between noise and resolution in the higher part of the audible frequency spectrum. In many cases they mistake noisy artifacts for crystal clear resolution in the higher frequencies.

As a keen amateur deep-sky observer since 1978, he uses the analogy based in astronomy. According to Dr. Yi, one way to get the best image of the moon, planets, star clusters and galaxies is to acquire a huge ultra powerful telescope. However the more powerful telescopes can cost a small fortune, so a more cost effective way to achieve the same objective is to find a location with less light pollution where even a modestly priced telescope will let you gaze at the heavens with enough clarity to enjoy the experience.

Carrying this analogy to music reproduction, Dr. Yi believes, the darker the background the better the image, be it visual or sonic. So in a nutshell, he believes that the lower the noise, the better the audio reproduction. He feels that this is the most cost effective way to achieve audio nirvana. He therefore pays great attention to the design patterns on a printed circuit board and then tries out many different parts before selecting the ones that lower the noise the most and thereby delivers the best performance. Well done Dr. Yi, the Femto DAC is proof positive that your approach works.  



If you have a budget of around $7,000 for a DAC, and if you have multiple digital music sources or plan to add digital sources in the future, you would be well advised to seriously consider the Femto DAC.  It is not exactly cheap, but it does offer good value for money. When you compare it to DACs in the $5,000 to $10,000 range, make sure that you are comparing apples to apples. If the DAC that you are considering does not offer a USB input and needs another component to make it USB compatible, then factor in the cost of the add on component and the cost of additional interconnects before comparing it to the USB compatible Femto DAC.  

If features like true high-end performance, comprehensive connectivity, bulletproof construction and build quality are important, you could do far worse than the Femto DAC. It may not retain its value as well or lead to a bidding war if and when you decide to sell it like some of the aspirational brand names do, but if you are not a compulsive, serial upgrader who succumbs to the temptation of splurging on new technologies or the latest and greatest at the drop of a hat, you can count on the Femto DAC to be your sonic companion in making beautiful music together for a long, long time.


Associated equipment:

CD Player - Bryston BCD-1 (SS)

Digital Player – Bryston BDP-1 (SS)

Amp - Ars Sonum Filharmonia (Tube) Ayre V3 (SS)

Speaker Cables - Cardas Clear Beyond

Power Cords - LessLoss Signature

Single ended and balanced Interconnects - Cardas Clear and Transparent Reference MM2

Digital - Transparent Reference (digital co-axial), Analysis Plus (Toslink), Cardas (USB)

Stands and Racks

Black Diamond Racing (The Shelf for Sources and LM series) 

Black Diamond Racing cones 

Shelf placed on bed of pure silicone sand, equipment placed on the shelf via the cones

The gear being evaluated does not receive any of these tweaks or enhancements.

Reference DACs - Neko Audio D-100 Mk2 / Benchmark DAC1 HDR

Power Conditioner -  Isotek Sigma II

Music server - Sooloos 5 complete 3-piece system, iMac (latest) with Amarra 2.3 and Decibel media players 

Software - Audiophile CDs from Cheskys, Dorian, MFSL and Sheffield Lab

Hi-res tracks downloaded from Linn and HD Tracks. MFSL LPs

Listening room – 90% underground, 18’ X 27’ X 8’ with extensive room treatments and solid concrete walls (with drywall over Roxul Safe & Sound) and concrete floor (Berber carpet).



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