PS Audio AirLens and DirectStream DAC Mk2 Review

We put bits of electronics, wires, and drivers together to create something ephemeral which we hope will also be ethereal. Digital bits seem a strange way to conjure music, but they are no stranger than the coded structure of our being. Someone wrote that code, just as someone wrote the code that operates the PS Audio AirLens and DirectStream Mk2 DAC. This article is about my interaction with these components, a matter of nostalgia for me, as about twenty years ago I owned its debut class D amplifier, the HCA-2.

In the ensuing twenty years, mostly class A and A/B solid state and tube amps have resided for a time in my room, but I have never given up on class D. There was something different, viable about the HCA-2 even though there were shortcomings tonally. At that time there was a gulf between the ripeness of class A or A/B and tube amps versus the sterility of class D. Not any longer! Now, the performance gap between the finest class A, A/B, D, and tube amps is vanishingly thin. After manhandling my share of heavy solid-state amps and superheating my over-built and well insulated listening room with tube amps, I am back to class D! The Legacy Audio i.V4 Ultra has been a gem and my mainstay for a couple years now – a veritable eternity in time of possession for a system builder. I am rolling at high speed with the i.V4 Ultra and finding them pleasurable in every parameter of sound quality with an expanding range of equipment. The more refined the systems that I build, the better they sound, the mark of a great amplifier.

Digital upgrade path

Over the years as I review, I have a tangential goal to upgrade my components, cable set, and speakers in approximate five-year cycles. This year the focus has been on the digital source. Consequently, I have been reviewing digital source components including the Aurender A20, Aurender N20, and Bricasti M1 Series2 DAC and M5 Network Player. I purchased the M5 as a flexible streaming component that will work its way into many rigs.

It would be nice if every component we liked had every input and output we desire to facilitate the utmost flexibility in building systems. Most do not, which is one reason why I own multiple components. Getting the most out of the equipment that one owns involves building many iterations of the system, trying all possible permutations. It is not possible to optimize a system by sitting and looking at it, waiting for it to do something. A system is optimized by manipulating the variables such as connections and cables to achieve a better result.

Ideally, my digital source would have all the standard outputs, including SPDIF (Coaxial), AES EBU, USB, and I²S, but most do not. Ideally, my DAC would have all these inputs, but most do not. I am continuing the search for additional digital front-end gear that might become a staple of system building because I wish to have every advantage in achieving sound quality that mesmerizes me.

The caveat with the Mk2 lies in the fact that it does not accept an input from a typical USB streamer. It has a USB input, but it is confined to network connections, i.e., attached to the local computer network. Thus, even though the Briciasti M4 Network Player is attached to my network, its USB output did not work with the Mk2. Especially irritating was the fact that the DAC was receiving the signal from the M5 but not producing sound. Evidently, a driver must be used to allow the MK2 to convert the signals from a device inputting via USB, relegating USB as a connection only for playback from a computer on the local network.

PS Audio’s rationale for that decision is because the company feels that USB is a noisier carrier to SPDIF or I²S. While that may be true, I caution the reader to take any blanket statement of standards with a grain of salt. During the AirLens and MK2 review, I had an in-depth conversation with a designer of a dedicated NOS (non-oversampling) DAC that has only one output – USB. That designer considers an external I²S connection to be redundant and inefficient and refuses to use it! That how the audio industry rolls; one designer swears off USB and the other promotes it! The audiophile is left scratching their head. I have encountered such contradictions consistently, so it no longer shocks me. In one sense, I could care less whether the favored connection is USB or I²S, may the best sounding connection in my system win!

I serve up audio systems like a cook serves fine dining experiences. As a system builder, owning multiple components is enriching and the more configuration options a component offers, the more I am drawn to it. The qualifier “quality” is critical. Aside from severe fiscal restraints, there is little point in having many mediocre options. This review will investigate not only the flexibility of the PS Audio gear, but whether its several options results in high quality sound.

All equipment discussed in this review is compatible with the user interface software ROON and Audirvana, and the music services Tidal and Qobuz. I operated these user interfaces using a Samsung S5 Tablet.

Arrival and features of the Airlens and DirectStream DAC Mk2

The AirLens and Mk2 arrived in their unique suspended isolation packaging akin to industrial bubble wrap built into the cardboard interior of the shipping boxes. There was a set of clip-on digital cable filters supplied with each unit and a pair of white gloves for handling the Mk2. I never did use the digital filters because the WireWorld Starlight Ethernet cable I use is physically incompatible with them. I also have used magnets as tweaks on cables previously and they failed my Law of Efficacy. I will pass on further discussion of PS Audio’s snap on filters.

The Mk2 is a complex component that has a full suite of inputs, two sets of analogue outputs (RCA and XLR), and a high output volume control that enables it to drive an amplifier directly. Integrated DACs are the up and comer in the industry, and the MK2 is a beauty! The multi-colored LED screen with a large, teal-colored numbers and letters has a selectable display wherein volume, sample rate, etc. can be enlarged for a quick glance. I appreciated the understated black case with rounded edges and illuminated sine wave swoosh, which reminded me of well-made Nike apparel.

The extensive Owner’s Reference (Manual) is online, and it covers the options associated with the main menu’s features; Balance, Phase, Pre-Emphasis, Versions (informational only), and the Sub-Menu items Audio Input, Audio Output, System, and Network.

The remote for the Mk2 was not available, so a PS Audio system remote had been tweaked to run the DAC. A note with the packaging instructed the owner to use two buttons that were reprogrammed to give full access to the Mk2’s features. I found the remote to work seamlessly with the DAC, but it is rather cluttered. As the manufacturing lag subsides, purchasers can request the Mk2’s remote be sent to them gratis. Even though the remote buttons are backlit, they are small. It would be nice to have a smaller, simpler working remote for basic operations of its DACs or preamps.

The MK2’s notable features include Pre-emphasis, which allows the user to counter recording techniques used on some compact discs which emphasize high frequencies. The owner can select On, Off, or Auto. The default setting is Auto. Other options allow inputs to be named, the ground on each input or output lifted, the shield or shell of an XLR interconnect lifted, and Polarity inverted. I was particularly interested in the Shell Lift feature, which the Owner’s Reference states may slightly improve the sound. There are many fine points to operation that can be studied by viewing or downloading the Owner’s Reference found at the PS Audio website.

Galvanic Isolation

PS Audio is trying to clear the digital air by ridding all incoming signals of noise and subjecting them into uniform processing. The primary technologies used in the AirLens are Galvanic Isolation and what the company calls Digital Lens Technology. There is a brief discussion of galvanic isolation on its website under the phrase “Galvanic Isolation”. I am reproducing most of it here:

The term galvanic refers to a galvanic cell, named after its inventor, Luigi Galvani. The Galvanic Cell is technically described with a mumbo jumbo of words: “an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell.”

More simply stated, it’s a battery.

This can be confusing because when we refer to galvanic isolation we’re not talking of batteries, but rather we’re referring to electrical isolation. A battery-operated flashlight can be said to be electrically isolated, but so too could we suggest a battery-operated DAC is electrically isolated, yet we’d be incorrect unless that DAC’s inputs and outputs are connected via optical cables.

And it is to this last point that we get to the heart of the matter.

To be galvanically isolated there can be neither physical connection nor direct electrical current involved. Even our old friend ground must not touch. In this way, whatever happens on one side theoretically shouldn’t be mirrored on the other side of the circuit.

The methods of achieving such isolation are to connect via non-physical means such as magnetic fields or light—hence the use of isolation transformers and opto couplers.

How does PS Audio accomplish the galvanic isolation in the AirLens? The website futureshop.co.uk had this explanation, “Typically, a common power supply provides ground and power to both inputs and outputs. Once a non-galvanically isolated device is connected to a noise source at its input, its shared ground passes the noise through a common ground to the output stage where the DAC is connected. The challenge with the AirLens was to design two fully isolated stages: input and output and connect the digital audio signal between the two without any loss. To do this PS Audio incorporated a low-noise galvanically isolated DC-to-DC converter to feed power to the AirLens’ output stage. The received digital audio data is then delivered to that clean output stage using only air as the interface.”

In layman’s terms, it uses a battery-to-battery interface to avoid electrical noise contamination. But will that make it sound inherently better than a renderer such as the Bricasti M5 Network Player? Comparisons must be conducted!