COS Engineering D1 DAC + Pre-Amplifier Review

Diving into the sound of the COS D1

In recent years I have spent a fair bit of time building streamlined rigs consisting of integrated DACs (DACs with a preamplifier functionality built in) connected directly to amplifiers. It is redundant in such a situation to insert a preamplifier, so systems including a preamp will not be given much consideration here. The scope of this review will include two other DACs, two amplifiers and two pairs of speakers. This will give enough perspective to appreciate how the D1 compares to other designs I have reviewed.

One of my favorite systems in recent years presented itself early on in this review. I assembled the following: Small Green Computer sonicTransporter AP i7 4T and SONORE Signature Rendu SE, Clarity Cable Supernatural USB (1m), COS D1, Clarity Cable Organic RCA Interconnects, Belles ARIA Mono Amplifiers, Clarity Cable Natural Speaker (shotgun), and the Kingsound King III electrostatic speakers with the VAC Royal Power Supplies. All power cables were the ANTICABLES Reference Series (Level 3) Power Cord, under review.

I could tell from my first listen that the D1 had terrific potential. I say “potential” because a component is never maximized simply by being inserted into a system. Any component can be elevated in performance over time as I learn how to play to its strengths. The appeal of this particular setup was the simple signal path; the COS D1 and the Belles ARIA Monos are clean designs without frills.

I appreciated the completely fatigue-free character of this system, which is not a given when using electrostatic speakers. The clarity of the ARIA Monos fit well with the Buffered operation of the D1. The ANTICABLE Reference Series (Level 3) Power Cords were the surprise! I thrilled to how they opened up the entire system and brought a very high degree of definition to the D1 without the stridency of some laddered DACs.

Things got even better when I substituted the Benchmark AHB2 Amplifiers in Mono Mode for the ARIA Monos. There was not much gained in the areas of cleanness and tonality, but the increase in power was appreciated, as the King III takes a powerful amplifier to open up the sound. The combination of the D1 with the AHB2 Amplifiers in Mono brought the King III closer to my reference sound for them.

The masterstroke that propelled the performance of the D1 to the best result with these speakers happened when I implemented what I call the Schroeder Method of Interconnect Placement. I discuss this more at length below, but it involves doubling up interconnects! Stop, impetuous readers! Do NOT leave this article and go to double up your interconnects without educating yourself to the risks associated with it in certain systems! If you wish to read about it after this review, feel free, at:

https://www.dagogo.com/audio-blast-schroeder-method-interconnect-placement/

In just a bit you will read how the Benchmark DAC3 DX was competent, but not able to defeat the D1 in a head-to-head comparison. The Benchmark AHB2 Amplifiers, however, were nothing short of stellar with the D1 when using the Schroeder Method. I am not boasting here about my discovery, but rather discussing a highly efficacious method that took the D1 as a source to a level of refinement beyond what is possible with normal interconnect placement. What follows is discussion of the sound of this system with comparisons between the COS D1 DAC and the Benchmark DAC3 DX.

“Space Dive-Opening” is the leadoff performance for the BBC/National Geographic soundtrack by Daniel Pemberton of Felix Baumgartner’s epic free-fall from the edge of space. The pulsing waves of the orchestra mixed with sustained LF bursts capture the sense of vastness to the event. The trilling of the harp recessed into the background lends an air of the ethereal. Between the need for resolution of the harp and control of the LF bursts there is plenty of room for error. Hearing this music on electrostatic speakers is a treat, as there is no other speaker technology that can create such a solid, enormous canvas of sound with such precision.

The D1 put up a good show, cataloguing the sonic bursts with a limitless character that hinted at the heavens opening up to receive its plummeting offering. The event was catalogued musically with intensity and vastness. The DAC3 DX closed the heavenly window a bit, and the LF pulses were less commanding, leading the senses to perceive a dramatic, if not epic, experience.

Dave Grusin has a lively rendition of “Peter Gunn”; I will never forget the instrumental version by Emerson, Lake and Palmer. In Grusin’s rendition there is a terrific amount of lower end band instrumentation, and the DAC3 DX couldn’t quite tease out the confluence of instruments. On the other hand, the D1 showed more insight into the congested bottom half of the performance allowing formerly abutted sounds to separate nicely to gain appreciation of the instruments’ lines entwined. With the D1 the band was swingin’ with loads of vibrancy.

Part of the problem for the DAC3 DX was the poor placement of the USB port literally right next to the 15A IEC socket. A typical round-barreled aftermarket plug will not allow the insertion of the USB cable! The only power cord in my collection that was workable was an older Harmonic Technology Pro-AC 10 that had a square body to the IEC plug. The COS D1 was already more incisive with the same power cord, but the D1 is not hindered in selection of such, so I moved to the ANTICABLES Reference Series (Level 3) Power Cord, and the gap in sound quality between the two DACs grew sizably. Here the D1 showed itself as an impressively refined integrated DAC, suitable for matching with an upper end stereo amplifier or monoblock amps. I would not hesitate to run the D1 direct into the finest amplifiers.

Inputs and outputs

I was disappointed to see that the D1 has no AES/EBU (XLR) input. This was quite a surprise since it has two optical inputs. This left me with practical use of the USB and SPDIF/Coaxial, one can certainly get excellent results with these inputs, too. I spend most of my time with file and streaming audio playback and I usually only return to Redbook playback and the SPDIF/Coaxial connection to informally compare the sound quality to file playback through USB.

If anyone doubts the potential of USB file playback and streaming audio, just this week I entertained local audiophiles who brought their discs to evaluate my system. We played the discs on a discontinued Musical Fidelity M1CDT Transport, which is a pity since in the past I had paired it with particular DACs and equaled the sound of not one but two $10K CDP players. My guests presumed the silver disc would be the reference sound of the system.

I enjoy nice little surprises, so while one of their discs was playing the Eagles’ “Hotel California” from the Hell Freezes Over album, nice sound, disgusting lyrics, I set up the streaming audio of the same track on the USB DAC input. I leaned over to them and like a school teacher in a mock terse manner put my finger to my lips, “SHHHHH!” They looked at me wide eyed as if to say, what’s gotten into him? I simply wanted them to hear uninterrupted the transition between the track on the disc and the streaming audio cached and played back through the sonicTransporter and Signature Rendu SE. A few seconds later it was playing via USB and both men’s eyes grew much wider when they realized it was playing via my tablet through the cached playback from the server, and it was head and shoulders above the CD! It seemed this was the first time they had heard a clear, direct demonstration of the superiority of streaming audio over CD. I hasten to add that this is not always possible, but the sonicTransporter and Signature Rendu SE are fabulous with USB DACs.

The little switch on the backside

Which brings us in meandering fashion to discussion of the little switch on the back of the D1! One little switch built into back of the D1 is the AC Voltage switch that allows you to match the voltage of the D1 to your country’s outlet voltage. This is important and a thoughtful feature for a DAC that is for connoisseurs across the globe. This is not the little switch I would like to discuss at length.

Sometimes curious little switches on components can yield very big changes. The Benchmark components have diminutive switches on both the DAC3 DX and the AHB2 Amplifier. The audiophile who owns them is well served to investigate them; I discussed them in the review. Likewise, the D1 has a second, wondrous tiny toggle named “BUFFER,” which recalls Buffy the vampire slayer. It’s laughable what people consider worthwhile entertainment. Let’s call this switch “BUFFER the Jitter Slayer,” since it at least has an important function, as opposed to fictitious vampire slayers.

COS provides the following description of the BUFFER feature in the Owner’s Manual:

There is a buffer switch on the back panel of D1, and it should be turned on for optimum performance. Sometimes digital music data do not move along and get converted in perfect tandem, which causes jitters, and even a few micros-second timing error is enough to perturb the ears and frustrate the mind. Therefore, D1 uses one-second depth buffer, along with an independent and accurate clock, to receive data, align them and send them out in precise time frames for conversion.

I’ll be perfectly honest here; there is just about as much I do not like about the character of the Buffered sound as I do like about it. It is apparent when comparing the two settings that the chief differences lie in the unbuffered presentation being perceptually “thinner,” that is, less robust than the Buffered operation. However, the Buffered operation is at times sounding congested due to an emphasis in the mid-bass.

I find a parallel in the two playback modes of the D1, non-Buffered and Buffered, to the difference between the PureAudioProject Trio15 Horn 1 Speaker and the Vapor Audio Joule White Speaker. The former is a hybrid two-way open baffle and the latter a dynamic three-way with full cabinet. Switching between them is a cause for surprise, as the leaner, tighter Horn 1 sounds perfectly full until replaced by the Joule White. Similarly, the Joule White seems very clean and transparent until the Horn 1 replaced it. In a similar fashion, if the D1 was offered in only one mode, the audiophile would be able to adapt the DAC to many systems without complaint. But since two options are offered, a tug of war ensues, the mind latching onto aspects of either mode’s operation that are appealing.

Those admiring a softer, less aggressive nature to their music will find the warmer, fuller aspect of playback with the Buffer engaged to be ideal, while those seeking a more “in your face” and stripped down version of their tunes will achieve it with the Buffer feature turned off. When the unit first showed up, my initial listening was with the Buffer operating. My first impression of the D1 was that it leaned toward being soft and somewhat indistinct and I am used to an exceptionally high degree of information retrieval. That impression changed when I began flipping between the two settings. I could hear that the unbuffered setting yielded a less rich result; the Buffer was not so much convoluting the sound as “thickening” up the sound.

A couple examples will suffice to elucidate the effects of the Buffer feature. The system used was: Small Green Computer sonicTransporter and SONORE Signature Rendu SE; Clarity Cable Supernatural USB (1m); COS DAC1; Clarity Organic XLR Interconnects; First Watt J2 Amplifier; Clarity Natural Speaker Cable (shotgun); Vapor Audio Joule White bi-wired. All power cords were ANTICABLES Reference Level 3 (review forthcoming).

The Buffer had an effect similar to airbrushing a portrait, or touching up a digital image. With the Buffer engaged Gregory Porter’s “Real Good Hands” was smooth, comfortable, with a generous amount of warmth, as though the lines of a face were filled in and softened. However, the edge, the urgency of the topic, his courting his true love and seeking her father’s blessing upon the suitor’s request for her hand in marriage, was also softened. The unbuffered operation stripped away some color, but the sense of pathos, passion and contrast was improved. Without the Buffer it was easier to identify minute details, Gregory’s voice sounded more raw and unprocessed, but like an untouched photo, there was less “perfection.” With the Buffer the song was woven tightly, drawing less attention to particular elements and more to the entire composition.

I had used this same setup with the Kingsound King III electrostatics and opposite to what most people would expect the King III was more forgiving on this track than the Joule White. I could run the unbuffered operation of the D1 on nearly any kind of music without fear of stridency. With the Joule White I had to be more careful because defeating the Buffer meant some music was harsher than I anticipated, thanks largely to the laser-like precision of the RAAL ribbon tweeter. Shelby Lynne’s “Just a Little Lovin’ “ is a reference for me as a test of micro dynamics and detail retrieval. It also is good for testing the refinement of the LF, the extension of the Bass as well as the cleanness of it. Shelby’s performance needed just a little lovin’ in the form of the Buffered playback. In this song the opening thwacks of the drum reverberating deeply across the recording venue set the stage for her rich, strain-free vocals.