PS Audio Stellar Strata Mk2 integrated amplifiers Review, Part 1 of 2

Kudos to PS Audio for bravery

Manufacturers are often quite sensitive about how much time is spent discussing competitors’ products in a review, understandably so. I have talked a fair bit about the Billie Amp Mk2, but for illustrative purposes. Fear not, PS Audio fans, the rest is about your favorite brand, and it performed even better than the Billie Mk2. That is no slight to the Billie Mk2. It’s a $2K integrated, but the Stellar Strata Mk2 at $3,700 is well worth the extra cash. If I were you, I would not hesitate in the least to pursue the dual Strata Mk2 if the funds permit.

In the DAC/pre/D topology of the Billie Amp Mk2, I wondered whether I had found an unusually capable integrated amplifier, or an outlandishly efficacious system configuration, or both. The only way to know would be to duplicate the system as close as possible with different pair of integrated amps. Enter PS Audio, one of the very few makers of an integrated amp with similar design, DAC/pre/D. In email exchanges to Paul McGowan, I had to explain myself a fair bit to convince him I was not looney. I must have sounded sane enough, as he granted the dual integrated amp review! I applaud him for his openness to such fiddling in the interest of advancement of systems. If the Strata Mk2 comes off looking extraordinary, and readers believe what I say about them, he may sell a shipload of them, and he rightly should!

Most of the designers I have met, and there have been many, would shut down such exploration due to overconfidence in their skepticism and fear of stepping outside the proscribed boundaries. Some manufacturers are so afraid of anything novel that they would soil their pants if anyone tried a novel setup. They fear potential public approbation above all, and it stifles their creativity. Paul seemed curious about the twin integrated setup. He should be, and so should you.

The obligatory information

The intent of this review is assessment of a pair of the Strata Mk2, so let’s first look at the Strata Mk2 as a single component. It’s lovely, brisk, tight, and tonally better than I expected for an affordable solid state integrated amp. I am not going to spend much time on the usual discussion of appearance and basic features because there are far more important things to talk about. Suffice to say, the Strata Mk2 follows PS Audio’s feature rich, layered operational design ethos. I like the trim appearance and neatly laid out backside. It has good build quality and has functioned flawlessly during the review period. It is shipped with ample packing. The remote is spiffy, not overcrowded like the DirectStream Mk2’s remote, and the interface with the unit worked flawlessly. It is easy to see the company is established and cares about reliability and the user experience.

The combo of DAC/pre/D is a winner, with a high level of precision and power enough to not choke on less efficient speakers. I cannot say if the unit will drive less efficient speakers to live or concert listening levels. I do not abuse equipment and have no desire to damage my hearing. I do not recommend listening at such levels, so you will need to find someone else to discuss that point. Again, the combination of DAC/pre/D is an unexpected pleasure, one that budget audiophiles with a yearning for upper end sound should note. I am elated that I selected the Stellar Strata Mk2 for review! There is something uncommonly efficacious about the pairing of these three functions in one unit, and I believe it changes the calculus of system building, another topic of my Editorial.

PS Audio has trickled down much of the performance and user controls of its higher line products. I rather like the options for displayed information on the screen. Some of the indicators are puny and indistinct from the listening seat. When changing the Filter settings, I found it nearly impossible to read the number despite wearing glasses. So much info is jammed into the display that some becomes illegible. Thankfully, the indicators for volume, data management, etc. are larger. The red or green dot indicator for the incoming signal (red = no signal, and green = signal) is very helpful.

The DAC handled every obscure codex thrown at it. Less common rates and bit depths like 88.2/16 and 96/24 did not faze it. There is flexibility in the design, as inputs allow for an external DAC and outputs allow use of an external amp. If you pair the Strata Mk2 with an external DAC or with external amp(s), you will get a different result that is possibly superior. Every system is discrete and must be built to determine whether the performance improves. Those configuration possibilities do not obviate the astounding result of using two units, but it does bode well for those willing to put in extra effort to potentially improve the Strata MK2. Based on what I am learning about system configuration from assembling systems, I am not sure I will build those iterations of systems with a single or pair of Strata Mk2. There are so many iterations of equipment that I cannot get to them all. Likely, you will not be building many iterations, incorporating extra components on hand, though if your goal is the best result, you should. Often, after the review is over, as I continue to build new iterations, the sound quality of the reviewed component continues to rise. The review is a snapshot of a particular moment in the process.

No one can predict the outcome of pairing an outboard DAC or amp with a single or pair of Strata Mk2, but based on its native performance, I believe such exploration would be worthwhile. As an example, when using the Billie Amp Mk2, I used the Line Out feature to incorporate the class D Legacy Audio i.V4 Ultra Amplifier in place of the Billie Mk2’s internal Class D amp. In that setup the Billie Mk2 handled the DAC and preamp functions, and the Legacy amp did the rest. The result was superior to using the Billie Mk2’s internal class D amp. It also provided more robust power to drive the King III speakers. I suspect the same might be true if an amp like the i.V4 Ultra was paired with the Strata Mk2, and given my experience, I would expect the Stellar Mk2’s performance with the I.V4 Ultra to be better. But systems must be built to know for sure. That in no way obviates what follows regarding my euphoria over the use of two Strata Mk2 units.

One caveat to this review is that I do not have a suite of PS Audio separates to compare the twin Strata Mk2. I suspect the odds are very good that the twin Strata Mk2 might outperform any given certain combinations of PS Audio separates. After all, they have outperformed by a long shot many very good, very notable components. PS Audio may not believe me, unless they build the system and hear for themselves. If they find it to be efficacious, they will benefit from designing a very high end dual mono integrated system either separately or in one chassis. The problem is convincing the ever-skeptical audiophile community that it is a superior system building method.

A weakness of my assessment is that I have not done direct comparison with all the equipment I am stating underperforms the twin integrated amp setup. Some will conclude that it is illegitimate, and here are my two responses to that objection. First, over the 17 years of reviewing, my reference standard has risen steadily. I march the sound quality upward and hang on to components that give the best sound. Secondly, I make a lot of systems with components, so I gain a good grasp of their innate capability. It is possible that a few combinations of high-quality components I used in the past would outperform the twin integrated configuration. However, based on the rising reference and the way that the twin Strata Mk2 blew past that reference sound, I judge it unlikely that past equipment would surpass the twin integrated amp setup. You must judge whether my criteria are legitimate. I caution you not to simply conclude due to skepticism or convenience that your combo of gear would humble the twin Stellar MK2 configuration. It’s that kind of presumptuousness that kills system advancement.

What does the Twin Strata Mk2 configuration look like?

The Stellar Strata Mk2 is a tight, refined sounding solid state integrated that is surprisingly inoffensive. At the price point one would not expect such a sweet result. Did I mention that I suspect that a good deal of the generosity of the twin integrated configuration is due to a DAC/pre/D topology? The benefits of a truly black background, a generous and informationally saturated rendering, and uncommonly warm tonality await discovery.

The Strata Mk2 combines three winning technologies. The DAC is based on the ICEpower module. Legacy Audio’s i.V4 Ultra Amplifier which holistically outperformed previously reviewed Class A, A/B, and tube amps, uses ICEpower. The input stage of the Strata Mk2 has what is called an Analog Cell, which relies upon MOSFET chips to control volume digitally versus in the analog domain. Digital volume control cleans up the signal and allows surprising amounts of fine details to be heard. The Exogal Ion PowerDAC employed digital volume control and was exceptional in lowering the noise floor and allowing minutia to be heard through the Comet DAC. The Strata Mk2 achieves the same result. The DAC uses galvanic isolation to separate the audio signal from noise associated with power. Now, imagine these three impactful technologies leveraged, and you begin to appreciate the potential of dual Strata Mk2!

When I reviewed the PS Audio DirectStream DAC Mk2, I quoted the company’s website and stated that while the description of the DAC sounded inflated, it was accurate. Now, I quote the company’s description of this integrated amplifier, “Here, engineer Darren Myers used the Analog Cell where he could lavish upon the music the sweet, tube-like quality of Class A biased MOSFETs. Combined with the ruler flat high linearity of Strata MK2’s high current output stage, richly overlaid layers of music’s inner details are preserved even in the most complex orchestral crescendos. There’s nothing like Strata MK2 when it comes to musicality.” There is some truth to that claim, however, I assert that there is nothing like two Strata Mk2 when it comes to musicality! Two are outrageously better than one!

Those who have set up passive bi-amping of speakers know the bump in performance achieved from dedicating the power supply and doubling the amplifiers used to drive a single speaker. There is a twist in the configuration of the system when a pair of Strata Mk2 are used. Because the digital signal entering it and the outputs are designated Left and Right, stereo, it would confound the speakers’ operation to simply connect both outputs of the respective integrated amplifier to one speaker. The result in doing so is that the channel separation will be mixed. That would introduce a noticeable amount of distortion to the speaker’s performance.

The proper connections are to dedicate each integrated amplifier to a set of drivers of each speaker. I configured one Strata Mk2 to drive only the bass drivers, its respective outputs Left and Right, sent to the appropriate speaker’s bass posts. The other unit drives only the mid/treble drivers, its Left and Right outputs sent to the respective speaker’s mid/treble posts. Proper polarity, positive and negative connections, are maintained throughout. The process becomes intuitive when you consider that most bi-wired speakers offer two sets of posts, one for Bass and the other for Mid/Treble. If you wire these integrated amplifiers as described above, you have accomplished what is called horizontal bi-amping. You can do so with bi-wired speakers in a traditional audio system that uses two amplifiers, each with a pair of outputs. I have tried that method in the past, however, in most cases, I felt that vertical bi-wiring, using one amp dedicated solely to one speaker, was superior. That cannot be done with the Strata Mk2 because it is a stereo integrated amp. If it were a mono integrated amp, like the Pathi, then one unit could be dedicated to each speaker. The bottom line is, one Strata Mk2 is used for bass and the other Strata Mk2 is used for mid/treble.

How good is this maneuver? It is everything! It is the ultimate! It is stunningly efficacious and will likely result in the best sound you have ever heard in your room regardless of previously used equipment. If your collection of separates is $50K or less, you should try it. I am aware these seem like absurd claims, and you likely do not believe me. Most will think, “Is he insane, suggesting I spend $7K to try dual integrated amps?” I am used to that kind of reaction. Some will believe me, try it, and find out for themselves.

Disappointment to elation with I²S

But it got better when I figured out how to use the I²S input! PS Audio makes much of its implementation of I²S, the signal transfer protocol inside most DACS. It is said to be cleaner and result in superior quality. It is the company’s preferred link between the AirLens and the Strata Mk2.

Could I split the I²S signal like the SPDIF, so that I could send identical signals to the two units? I knew it was a gamble because I²S is intended to be used point to point, not point to two points. (At this point the community is cleaved, with half thinking I am an idiot, and the other half contemplative, “If he succeeds, what are the implications?”) PS Audio uses HDMI cables to transmit this signal. I still had the Audioquest HDMI cables from the DirectStream DAC review, but I needed a way to double the signal. I researched it and found no definitive evidence. After all, who is crazy/dumb enough to try to split an I²S signal? Me! I fully expected there to be some degradation from splitting it, but as I had already demonstrated with the SPDIF (coaxial digital) signal, I suspected that the overwhelming benefits would far outweigh the losses.

I talked to cable makers about using an HDMI splitter, and they said it wouldn’t work. HDMI is a different protocol, and the signal would not come through. But I used Audioquest HDMI cables for the DirectStream DAC, so what did I have to lose? I went to Best Buy and bought both a powered HDMI splitter and a passive USB to dual HDMI adapter. The staff was split (pun!) on their opinion whether either would work. Neither device worked. I was dejected and nearly quit at that point. I am SO happy that I didn’t quit!

I emailed Paul and told him the splitters didn’t work. He saved the day by suggesting that I perhaps try an HDMI Y-cable, if one existed. Such cables exist, but they are junk products sold on sites like Amazon for about $10. Now, some of you are thinking, “Why is this guy an audiophile reviewer? He doesn’t know anything about design or electrical theory!” True. But if I find a method or system configuration that is a performance outlier, then it’s not stupid. Keep reading.

What if splitting the I²S signal wrecked the circuitry in the pair of Strata Mk2? Then I would have a problem, an expensive problem. But what is life if you risk nothing? Boring! What is audiophilia to me if I don’t try anything interesting? Boring! It is worth it to me to put some money on the line in searching for the outlier, the absurdly efficacious system. When I have reason to believe in an alternative configuration, I am willing to spend money if it can pay off handsomely in performance. It takes guts to pursue a configuration that every industry member I spoke with (except Paul; he didn’t say anything much but gave the go ahead) had reservations. I held my breath as I turned on the units, looking hopefully for… A GREEN LIGHT! It worked! The I²S signal was successfully split and received by each unit! But would it sound good or distorted?

Extraordinary experiences

Do you Remember the first time you went to the symphony and were enraptured? Do you recall the first kiss with your lover (in my case, my wife of 32 years). Have you ever climbed up to the Sun Gate overlooking Machu Pichu, been on the Great Wall of China, seen the Taj Mahal, swam with stingrays or skydived? I have been blessed to have done all those things. Do you understand what I am saying? This was not just another of the dozens of incremental improvements from adjusting traditionally configured systems. This was entirely better, a new way, a new era opening for me! This is the only system configuration under $10K that has ever bested upscale separates, very fine, expensive separates. We are talking many dedicated components in traditional configurations averaging from $50-75K!

This result was while using two different Audioquest HDMI cables. Yup, this was not even a kosher cable setup. I violated one of the most basic rules of system building which calls for consistent cabling to amplifiers. Why? Because I did not have two of the same cable, so I did the next best thing and used two very similar HDMI cables. There is no way, absolutely NO way that this getup could sound good, especially when using to different HDMI cables to the integrated amps. Right? Wrong! I knew I could get away with it, because during the DirectStream Mk2 review I commented that the sonic differences between the Cinnamon and Thunderbird HDMI cables did not pass my Law of Efficacy. That meant they sounded so similar; it was not possible to easily distinguish between them. Ergo, they would work well enough as a pair for this experiment, and they did. That is not to say a homogenous pair would not sound better (I will get that opportunity when the additional Audioquest HDMI cables arrive), but that they were close enough to hear what the system was doing without noticeable Left and Right variances. The result is the equivalent of an economical rig with one hand behind its back whooping many more prodigious rigs.

Speaking of variances, when using the remote to change the Filter setting on the units, if one changes and the other does not, causing two different Filters to be used, it is instantly noticeable and unpleasant! There is a warpage of the sound stage, and it literally sounds distorted. It snaps back into place when the Filters mirror each other. Conversely, the different HDMI cables produced no warpage or skewing of the sound stage, and the tonality was so close that a person who did not know would not suspect they were different, which confirmed my assessment that they had not passed my Law of Efficacy.