The Calyx Femto DAC

Device Type: Digital to Analog Converter
Input: Asynchronous USB Audio Class 2.0 : Up to 24bit, 44.1, 48, 88.2, 96, 176.4, 192 kHz; Two Coaxial, Two Optical, Two AES-EBU, BNC; S/PDIF Up to 24bit, 44.1, 48, 88.2, 96, 176.4, 192 kHz
Output: RCA (single-ended) or XLR Balanced
Dimensions (H x W x D): 4.25 inches X 17 inches X 15.6 inches
Weight: 40.5 pounds
Availability: Authorized Dealers
Price: $6,850.00
US Distributor's Website:
Manufacturer's Website:

There has been a movement in the design of high end DACs to reduce jitter to extremely low levels due to the emergence of extremely accurate oscillator-clocks. Recently, I reviewed the MSB Technology Analog DAC with its Femto clock and claims of extremely low jitter. Calyx Audio, a division of the Korean manufacturer Digital and Analog, have utilized an extremely accurate clock to decrease jitter from the standard picoseconds to femtoseconds ; in this case 500 femtoseconds. One femtosecond is one quadrillionth (0.000 000 000 000 001) of a second or 10−15. Calyx is obviously proud of their clock technology and named their flagship DAC Femto. Digital and Analog not only builds a line of DACs, but also Class D amplifiers and a powered speaker. They have specialized in building class D ICs and Full Digital ICs OEM since 1999. In 2008, Calyx Audio was formed to produce high end audio products.

While removing the Calyx Femto from its packaging, I realized that this was a serious audio product. The DAC tips the scales at 40.5 pounds and it appears to be physically well built. The high quality brushed aluminum case is extremely attractive and reminds me of the Esoteric Audio high end line of DACs. There are 7 small selector buttons on the front panel to control volume, input, phase, filter and mute. The on-off button is located on the left side of the DAC suggesting that the Femto be left on for best performance.The feet used on the Femto are unique in that they are made of cork and no doubt, contribute to the overall sound the designer was trying to achieve.

The Femto Features

  • The Femto supports asynchronous USB utilizing an ESS Sabre 9018 32 bit dac / channel.
  • The DAC also has S/PDIF inputs and optical inputs. Two Coaxial, Two Optical, Two AES-EBU and a BNC are included along with the USB to make this a very versatile DAC. Both the USB and S/PDIF inputs support up to 24/192 kHz.
  • The Volume control is a 32 bit digital control that changes the volume in .5 db steps. When the front panel display indicates 100, the volume control is bypassed for use with a preamplifier.
  • Three filter selections are offered; 50, 60 or 70 kHz.
  • The display is large with orange lighting that indicates the input, sample rate, and volume level.
  • Both single end and balanced outputs are provided with the Femto.
  • The linear power supply of the Femto is shielded in its own case and has dual transformers; one for the digital and one for the analog sections.
  • The Femto comes with a nicely machined aluminum remote providing the same functions as the front panel selectors.
I presented several questions to Seungmok Yi, designer and founder of Digital and Analog and Calyx Audio. His answers to my questions follow:
The Femto uses custom clocks derived from aviation and aerospace industry applications. The Femto clocks are encased in 3 metal cases. The performance of the clocks is considered state-of-the-art and contributes to the Femto’s excellent low jitter specifications.

The 3 filters are modified ESS Sabre filters and not the stock filters.

The power supply in the Femto has 2 custom transformers that are encased to provide shielding to the analog stages. The power supply uses LDO ( low-dropout regulators ) to each IC in the power supply. These LDOs offer very low dropout, fast transient response, excellent line and load regulation.

There is isolation of the incoming power to the USB receiver from the computer to protect the analog stages from computer noise.

Contributing Components and Software to the Femto Review
Equipment Used in Evaluation: MSB Technology Analog DAC with Analog Power Base, Early 2011 MacBook Pro 2.3 GHz Quad Core i7, 16 GB RAM, Samsung 840 Pro SSD, Promise Pegasus Thunderbolt Drive 8TB, GRAID 8TB Thunderbolt Drives. Audirvana Plus/OSX Mtn Lion, JRiver, JPlay/Windows 8 Pro 64. Interconnect cables: Synergistic Research Tesla Apex LE, and Tesla Precision Reference LE. Speaker cables: Synergistic Research Tesla Apex LE. Power cables: Synergistic Research Element C.T.S. Digital, Tesla Hologram D, T3, and Precision AC cables. 2 Synergistic Research Tranquility Bases, USB Active SE cable and Thunderbolt Active SE cables. Other USB cables on hand were the Audioquest Diamond, Synergistic Research Active USB SE, Light Harmonic LightSpeed, and the Wireworld Platinum Starlight.

I had excellent results using the Synergistic Research USB Active SE powered by the Transporter Ultra SE with the Silver Enigma tuning bullets.

Audirvana Plus 1.5.6 was extensively used in this review. The latest version sports a new feature that allows you to select the Priority of Audirvana. I asked Damien Plisson of Audirvana to describe this feature:

“The priority setting (High, Priority, and Extreme) sets the priority of the Audirvana Plus process over the other ones running on OS X. This helps to ensure that the audio playback routine will not be interrupted or postponed when feeding audio, and thus ensures the timings are much more accurate. And the audio signal transmission is done in the shortest period of time (no interruption), reducing the generated interferences of the computer activity.”
The Calyx Audio Femto supported Integer playback with OSX Mtn. Lion.

General Sound Characteristics of the Femto
It did not take me long to discover that the Calyx Audio Femto is an excellent sounding DAC and very competitive with the other high end DACs I have reviewed at this price point. The soundstage of the Femto is wide with perceivable depth that I would rank as very good when compared to most other similarity priced DACs. The Femto has an upfront presentation with excellent detail and focus. The sound is slightly dry with a greater emphasis on fundamentals with less emphasis on the overtones with a short decay. The DAC is quite free of digital artifact hardness and definitely avoids long term listening fatigue. Both macro and micro dynamic contrasts were very well reproduced with the Femto. I did not find large differences between the 3 filter settings, but did prefer the 1st filter. I felt that this filter was the best balanced and the most neutral sounding of the three in my system.

Self-Powered USB
Using the Light Harmonic LightSpeed Split Configuration Cable with a separate USB A for the 5 volt line from the computer, I found that I was able to initiate the handshake connection with the USB reciever and then disconnect the 5 volt line with no loss of connection with the computer. Removing the 5 volt line improved the sound of the Femto. I found the soundstage to get a little bigger and voices and instruments to be a little smoother and fuller sounding. Granted, it wasn’t a huge difference, but it was one that I was able to perceive. And given that the difference was small indicates to me that the Femto’s USB receiver is well isolated from the analog sections of the DAC.

The Digital Gain Control
I did play the DAC utilizing its balanced outputs with the digital gain control, but found that I preferred listening through a high quality preamp like my Ayre KX-R. Given the 6.8 volt rms output through the balanced outputs, the volume setting was less than ideal for my system. I felt that playing the Femto through the Ayre simply sounded better, Given the Ayre’s advanced volume control using Variable Gain Transconductance (VGT) produced the optimum signal to noise ratio regardless of volume setting allowing the Femto to display its excellent characteristic of low noise.

The physical layout of the panel controls and those on the remote were a pleasure to use and obviously well thought out.

The Femto is One Quiet DAC
One of the first qualities of the Femto that grabbed my attention was just how quiet it is. I’m not only talking about background silence, but the reduction of noise that also contributes to a “smooth” grain-free sound with less digital irritation. The Femto floats a very large soundstage with a deep black background. The more I listened to the Femto, the more I was impressed with this low noise quality that allowed voices and instruments to be extremely well focused with reproduction of the original acoustic space of the recording.

I listened to the first track of Jen Chapin’s recording reVisions Songs of Stevie Wonder Chesky Records 24/192 (HDtracks) and heard one large acoustic space with the saxophone off to the left of the soundstage and the bass to the right. The recreation of this large acoustic space with the Femto was one of the best I have heard with this recording. The focus and resolution of the instruments and voice were very impressive.

While everything in the design of the Femto contributes to this low noise attribute, I suspect that the attention to the design of the power supply and isolation of the digital from analog sections has a good deal to do with this low noise result. Also, the extremely low jitter of the Femto Clock is a contributing factor.

Just How Quiet Can the System Get? The Synergistic Research PowerCell 10 SE MK III
I recently changed my amps from Levinson 33H to Ayre MX-R mono blocks. The 33H amps had a unique feature; they had a separate internal amp that provided AC power regeneration to the voltage gain board. This feature did seem to lower noise from the AC line and negated the use of an external power conditioner. I have found over the years that most amps sound better plugged directly into the wall socket instead of a power conditioner. Most power conditioners seem to limit current while others seem to reduce dynamics at the expense of providing a smoother sounding presentation. The Ayre MX-R does have a built-in Ayre power line RFI filter, but the Ayre manual suggests that “in some situations a high-current power-line filter may provide additional sonic benefits.”

I tried plugging my amps into my $8500 Shunyata Hydra V-Ray II and its Cobra CX AC cord, but the results were less than satisfactory. I then tried the Synergistic Research PowerCell 6 SE $2595 with its Element Tungsten AC cord that I used in my review of the Transporter Ultra SE (see review. The PowerCell claims to not limit current to the devices plugged into it. I had excellent results with my DAC and Transporter Ultra SE plugged into the PowerCell, but had never tried my Ayre amps with this conditioner.

The PowerCell 6 SE with the Element Tungsten AC cord was not a totally satisfactory combination with my two Ayre MX-R amps. The Element Tungsten AC cord did sound very good with DACs and other sources, but these high powered amps were not an optimum match. While the sound did improve in some areas, I felt that the amps were not opening up with the Element Tungsten AC cord provided with the PowerCell 6 SE.

I spoke to Synergistic Research about the use of the PowerCell 6 SE for the Ayre amps, and their recommendation was the PowerCell 10 SE MK III. The $5500.00 PowerCell 10 SE MK III comes with the Element Copper Tungsten AC cord, an $1800 AC cord better suited to high current demands than the Element Tungsten cord. Also the PowerCell 10 SE MK III offers superior AC line conditioning given the larger size of its PowerCell and the inclusion of the Ground Plane technology used in the Tranquility Base. Listening to the Femto with my preamp and amps powered by the PowerCell 10 SE Mk III resulted in the background silence improving significantly becoming very dark, with increased definition of the midrange and highs, a larger soundstage, and better control of the bass. The amplifiers opened up with no constriction of dynamics or bass. In fact, macro and especially micro dynamics were enhanced and beautifully reproduced with a natural relaxed character with non-fatiguing definition.

I felt that I was not able to fully appreciate the low noise of the Femto without using a line conditioner on my amps. Obviously, the quality of the AC varies given your location and time of day. But I will now go on record that the PowerCell 10 SE MK III powering my sources and amps has become an essential reviewing tool for my evaluation of components.

Janos Starker Mercury Living Presence
Given the significant reduction of AC line noise from my system, I was now ready to listen to the Bach Cello Suites 24/176.4 (HDtracks). The SACD recording was converted by Bruce A. Brown for HDtracks and the result is excellent. Janos Starker completed the recording of the Bach Cello Suites in December of 1965 at the Fine Recording Studio A in New York City. I have the original highly sought after Mercury early pressing LPs of this wonderful recording. The Femto did an excellent job of reproducing this recording. The acoustic space of the recording with its ambiance was easily heard with the Femto as was the movement of the bow across the strings and the resonance of the cello. The focus and resolution of the Femto was impressive.

Playing With Fire
This Reference Recordings HRx 24/176.4 recording is a stunning example of a big sounding dynamic recording that will put your DAC and system to the test. Jerry Junkin with the Dallas Wind Symphony are paired with the 7-piece Jim Cullum Jazz Band in the composition "Playing With Fire". The recording has a wide dynamic range that is similar to the other HRx symphonic recordings. For those of you familiar with previous Dallas Wind Symphony recordings on Reference Recordings, you’ll know what I mean. The Femto was a delight to listen to with this recording. Drum solos, massive horn section, and a Dixieland style jazz group accompanied by the Dallas Wind Symphony proved to be a good test for the Femto. The Femto had no difficulty reproducing the complex passages with excellent delineation of the different instruments with no congealing of the multiple voices. The ability of the Femto to unravel complex musical passages was first rate.

A DAC That Does Everything Well
The Femto did a wonderful job playing whatever genre of music presented to it. From Nine Inch Nails to Joni Mitchel to Wayne Shorter, the Femto handled everything with exceptional musicality. Detail, transient reproduction, macro and micro dynamics, focus and ultimate resolution were in a first class category. I just could not find fault with the Femto.

Comparisons to Previous DACs Reviewed
The Playback Designs MPD-3 at $6,500 (see review) had a similar forward perspective with excellent detail, dynamics, and speed. The Femto presented a larger soundstage in both width and depth. The Playback Designs had a greater feeling of smoothness or less dryness to the sound perhaps the result of its double DSD output. This is not to suggest that the Femto is the least bit hard sounding, but the Playback Designs MPD-3 sounded more like the qualities heard with a good native DSD file. Also, the MPD-3 is capable of DSD 64 and DSD 128 playback and supports sample rates up to 384/24.

The MSB Technology Analog DAC ($7,000 see review) was very different sounding compared to the Calyx Femto. The Analog DAC with its standard Desktop Power Supply sounded more laid-back and exhibited less presence in its presentation. The Femto sounded more vivid with a greater emphasis on detail and focus in the upper midrange and highs. The Analog DAC with the standard power supply had a wider and deeper soundstage compared to both the Femto and the MPD-3. The Analog DAC also had a more relaxed sound that some would equate as “analog” sounding.

Upgrading the Analog DAC with the Volume Control, and more importantly, the $3,000 Analog Power Base power supply resulted in a DAC that was now $11,000.00. The Analog DAC with Analog Power Supply had the large soundstage of the basic Analog DAC, but now with the focus and speed of the Femto. The upgraded Analog DAC matched the Femto in overall quietness but at a significantly more expensive price. The upgraded Analog DAC with the Analog Power Supply was fuller and more analog-like than the other DACs. Also, both versions of the Analog DAC support DSD 64, 128 and sampling rates up to 384 kHz.

The Calyx Femto, by anyone’s measure, is an impressive sounding DAC. The well designed power supply, very good isolation of the digital and analog sections, and the state-of-the art clock technology all contribute to its excellent performance. The only thing that left me wanting was the absence of native DSD support. Perhaps Calyx Audio will add this feature in future updates. But that aside, the Calyx Femto will please many listeners with its special qualities.

Associated Equipment

christopher3393's picture

Steven, In my opinion this is a very helpful review in part because it is carefully and thoughtfully done. Thanks.

I wonder, do you have a second system that might provide broader insight into the dac"s capabilites?

It is not unusual for reviewers to use A) the equipment at hand and B) for that equipment to be reference quality. The problem that this leads to for me is exemplified by reviews that quite reasonably do not favor the digital volume control to the analog control on their reference pre. It has been hard for me to discover how much I have to spend on a pre to get significantly better quality volume control. In my case that includes interest in the quality of sound for low volume level listening. I've yet to see a professional review that says " Here is a somewhat affordable pre that will do a much better job controlling volume than this dac and a number of other dacs with digital volume control". That would be a real gift to me. For example, the Ayre Acoustics KX-R was preferable for volume control. But would that also apply to the Ayre K-5XE MP?

Now in no way would I expect you or Michael to be able to do this unless you happened to have suitable review equipment available at the time, or could easily shift the review component to a second, humbler system which Michael as well as other reviewers do as best they can. But sometimes issues like this one do seem to fall between the cracks in the audiophile journalism world.

Steven Plaskin's picture

Hi Christopher,

Your points are well taken and unfortunately, I don't have another system.

The Ayre K-5XE MP is an excellent preamp. I would probably prefer the Ayre with the Femto. But a number of our readers prefer to remove an additonal component like a preamp and would be very happy to use the Femto's gain control. I guess in the end, you would just have to try it.

Perhaps Michael can give me a big raise for a 2nd system angle

silvertone's picture


Thanks for the review.

In your opinion what prevented the Calyx from getting the 'greatest bits' award?  Is it the lack of DSD support or the sound was not up to par with other DACs?




Steven Plaskin's picture

This DAC is definately on par with other DACs I have reviewed. I would have liked to see DSD support.

bsm's picture

The feet used on the Femto are unique in that they are made of cork and no doubt, contribute to the overall sound the designer was trying to achieve.

What qualities would the cork contribute?

Steven Plaskin's picture

You and I both know that every material used for feet resonates at different frequencies. Some dampen a range of frequencies.  You would have to ask Calyx Audio why they selected cork. It is not a common material used for feet on an audio product.

bsm's picture

My apologies for questioning your baseless assumption.

Steven Plaskin's picture

I do know that the cork material was selected for its particular sound. I'm sorry that I can't be more specific. 

bigrasshopper's picture

Or, you could send Micheal the review sample for a second opinion on the second system.  When you sent the MSB Dac to him I thought it was very valuable to hear the same unit from a different perspective.  But I know it's not the same.  I also thought it was interesting that Micheals favorite Dac seems to be the Mietner so far, that was my impression.  So I was disappointed that Steven did not weigh in on that unit.  Was that your choice Steven ?     I think doing intra-site comparisons helps to unravel the unit from the system from the listener..helps.  I guess you guys have chosen different towns and differnt Dacs ?  Nice review by the way.  This is one Dac that has aroused curiosity.

oscar_nr's picture

Thank you Steven for your good review.
As owner of this DAC I think that your comments are spot on. I agree with you that one of the main streghts of the Femto is that deep black background from where music flows. This DAC works more substracting noise to the listener than adding filters, etc to the chain. It is a very clean (not sterile) DAC with null digital hardness and superb musicality (as effortless comunication of the music reproduced). Curiously, the great focus, soundstage and detail it shows does not magnify the flaws of recordings. I use it most of time with redbook rips and even not-so-good recordings sound very very listenable, better than I never suposed. Obviously, good recordings sound superb.
BTW, I do not think that there is any work in progress to add DSD to the Femto (although the chip inside could support it). I do not use it, but it could be a fantastic addition.

Best regards

silvertone's picture


Did you also find some of the 'dry' sounding observation Steven mentioned?

What does the rest of your system consist of?



oscar_nr's picture

Hi, silverstone. I haven't any of the DACs Steve compared the Femto with, but I wouldn't say it as a dry sounding DAC per se. Many of us almost equate 'dry' to harsh or 'digital' (and I think Steven do not consider it in that way). It has a lot of detail and is not laid-back by any meaning, but like I said in the previous post it sounds very natural and it is not the kind of musical  flaws microscope amplificator that one associate with a DACs like the dcs debussy. In fact I feel that the listening fatigue is negligible ( I can listen for hours without  any fatigue, and my musical habits aren't audiophile recordings precisely). Like I also said before I think that that is related with the substraction of the maximum amount of digital noise from the chain, leaving a clean 'message'.

My system are Mcintosh tube preamp and Mc power amp to focal scala utopia loudspeakers. The USB input is excellent and I use a MBP, amarra and a Tellurium Q black diamond USB cable.

If you can test the Femto. I do not think you will be disappointed. You can't go wrong with it or with the MSB Analog, for example. It is more related with  equipment synergy and sonic preferences, or need for native DSD.

best regards


Steven Plaskin's picture

Please don't take the statement about the DAC being "dry sounding" as implying that it is the least bit hard or bright. The Analog DAC ( Desktop Power Supply) is warmer sounding and less detailed sounding than the Femto. 

I agree with Oscar's statement about system synergy and personal preference. My reviews are just starting points and should not replace listening to these DACs in your system.

Axiom05's picture

"My reviews are just starting points and should not replace listening to these DACs in your system."

If only this was so easy. No offense intended, but unfortunately things can be quite different out here in the real world.

Steven Plaskin's picture

I hear ya Axiom05. I live in San Diego, but even in a city this size, I can't audition most of the DACs I have reviewed.

This is why Michael, Jason, and I try very hard  to accurately describe what we are hearing as well as comparisons of the DACs.

I do appreciate your comments.

Best regards,



oscar_nr's picture

I undestand your frustation, Axiom05. I had to buy my Calyx femto blindly, because there were/is no even distributor in my country. And doing home demo trials are almost impossible. I tried to contact recently with MSB distributor for doing a home trial and not received even an answer, so I did not go further looking for their analog DAC. Sad but true. Anyway, I concur with Steve that your perceptions/synergy equipment match could be different and the last word is to test it.

bigrasshopper's picture

Forgive me for thinking out loud, but Im just trying to imagine a way to sample a Dacs sound and send it to people for virtual listening.  Fremer does this with analog sources through various cartridges by converting to digital and making available for download.  I have to say that I have not tried this, but apparently, something meaningful seems to be getting through.  It would seem impossible to hear anything better than your own Dac, but you might be able to hear certain sonic signature  differences.   If I thought I could hear a significant difference virtually, it might make me more motivated to listen in person.  I happen to be very happy with my current cartridge.

otaku's picture

Something seems odd to me:

" I found that I was able to initiate the handshake connection with the USB reciever and then disconnect the 5 volt line with no loss of connection with the computer. Removing the 5 volt line improved the sound of the Femto. "

If that is true, then couldn't Calx spend 50 cents to include a relay to disconnect the USB's 5v when the connection is made?