Anyone listen to Zu Audio's Definition Mk3?

>>What I noticed with the Sophia’s in reference to the M60’s is that they were a little sweeter, had a little more “density” to the midrange tone, and a little more sense of coherency or “cut from the same cloth” sound (at least from upper bass to treble); however, the latter seemed, upon further listening, to be a coloration imparted on all music and ultimately became a bit of a distraction.<<

All of this is consistent with what you should expect from competent SET v. push-pull -- even OTL. However, I cannot reconcile your statements. At least within the terms you chose to use, I don't know how "coherency" can be judged a coloration. It can take awhile to get used to, after years or decades of hearing push-pull crossover notch grunge, subtle as it is, as normal. But I'm guessing that whatever you heard as a coloration was something else about the Sophia. I don't regard the Sophia 845s as objective as the Audions, but they get closer than most competing 845 SET amps. The Sophia design is a more in-your-face presentation, and that's not just a function of acoustic energy. It's more aggressive.

>>There was also something going on in the upper midrange / lower treble that showed up on some tracks.<<

That something was likely the 845A tube's signature upper midrange glare, which the B tube mitigates, as does (to a lesser extent) the 845A Cryo. I know why amp makers ship with the 845A (it's dirt-cheap and consistent) but I don't know why any of them insist that's how their amp sounds best -- it doesn't. Not anyone's. I can't listen to the Sophia happily either with the stock tube. There is also some further tunability in the Sophias via the input, driver and rectifier tubes. It's not as simple a circuit as Audion's. The downside is less palpable intimacy and finesse. The upside is you have more tubes to roll for custom contouring!

>>The Atma M60’s had significantly more drive, a larger soundstage, more air on top & weight on bottom, though none of the aforementioned was perceived as lacking while listening to the Sophia’s.<<

Ralph's M60 is a muscular amp and it has deep bass performance more precisely defined and textured than almost any SET amp. Can't comment on the soundstage differences since when I've heard both of those amps, soundstage was as large as I could want, appropriate to the music and the room. That none of these comparative shortcomings were perceived when listening to the Sophias shows vividly how subjective evaluation is. A/B comparison can make both contenders sound "wrong."

>>I have heard that the Sophia’s have a lower noise floor than the Audion’s?<<

They have in the past, though to me the difference was not actionable. Audion has recently changed their power transformer shielding and made some other internal wire routing changes, in part based on results from some work that Bob Hovland did on my Black Shadows. These amps are now as quiet as Sophia's, which were the quietest 845s on the the market, previously. You can also run the Audions very quietly by virtue of their high input sensitivity. If you have ample gain in your preamp, you can run the input level controls quite low and use more of the gain in a quiet preamp. In any case, this nosie floor difference between the two brands' 845 amps is now effectively moot.

>>Although noise didn’t significantly factor into my evaluation of the Sophia, I wouldn’t want it to be too much higher. Can this be a distraction with the Audions?<<

I'd need to know you much better to say. I've been listening to tubes my whole life, and vinyl too. What's a little power amp noise after all that? Power amps are quiet compared to recordings and sources. There's noise in the world, including at any live performance of music. Compared to my guitar amps, my hifi amps are silent. I didn't consider noise a problem with my Audion power amps before and they're over 10db quieter since Hovland had a go at them, so I never think about it. on the other hand, I know people who love the sound of a tube amp but because of scant spurious noise, they listen to solid state they enjoy less. People are funny.

Phil

>>From what I surmise from some of his writings, room acoustics, power conditioning, and wire are a waste of time.<<

This is not nearly a correct summation of what I think about these topics.

Power condition is difficult to prescribe. That is, the precise results in any given home and system are not strictly predictable. I use voltage correction, isolation, and on my sources, balanced power. All these have been helpful to me. I generally recommend large balanced power isolation transformers as the most cost-effective power "conditioning." But I've also heard installations where no conditioning sounded unmistakably better than any alternative. I can recommend balanced power unconditionally, but I can't predict exactly what method power conditioning will be best for you.

I've never written that cabling is not valuable. I have written that I have not found much correlation between cable price and contribution to sound quality. I've also written that I view cables as having distinct sound signatures -- that they are effectively "fixed parametric equalizers" -- and there are more important aspects to pay attention to if money isn't unlimited. The role of cables is affected by context. I prefer soncially neutral cabling that is also practical to use. That excludes most of the cable on the market.

On acoustics, I've written that room treatments tend to underperform though in some rooms, an acoustic dysfunction may be so egregious that correcting for that is indispensible. A friend has a room that without elementary treatment, it's first-order dysfunction simply builds cumulatively, like a figurative sonic Hadron Collider. Fixing that is worthwhile regardless. But most treated rooms end up overdamped and unnatural. My personal preference is to eschew dedicated listening rooms, keep the hifis out in the open living areas of my home and mitigate with room furnishings and placement. The rooms are to live in first, to optimize for sound second. Here's the thing: No matter the room, I can always hear the signature(s) of the gear through the prevailing acoustics, and that defines the actionable elements to what I'm hearing. But the room as an acoustic environment becomes just that -- environmental -- and easily forgotten. Put another way, no room has ever gotten in the way of me enjoying music, but much gear has proven too deleteriously distracting be enjoyed.

Phil

>>Question for Phil: do you have any addendums to add to your room philosophy in light of recent experience with Keith and panels, etc?<<

Keith has a severe first order acoustic dysfunction in a nearly square space. We couldn't take down his ceiling panels but Defs mitigate floor and ceiling effects much more than the speakers he owned when he had the room treated. So put that aside. But it was easy to remove his reflection-points damping panels. In that space, removing the damping panels had the effect I expected, but worse --- the room goes "runaway" -- a sonic Three Mile Island in the making. It also eats bass below 100Hz or so, like a grizzly romping through a salmon farm. The Def4 sub eq helps there. I've never chosen to live in a space that mandated a virtually square acoustic domain for listening. If I had a first order problem like that, I'd minimally treat it too.

But I don't. I have normal US sheetrock-on-frame aberrations: some rising bass response, a little slap echo, some excitable sheetrock glare when I run Duane Allman or Hound Dog Tayler a little hot. But the tonal integrity of the system and room is solid, and imaging is as good as it gets in a 14' x 21' space -- smaller than Keith's uni-room -- where I can't place the Defs far from the boundaries. Interestingly, aside from the differences in our respective rooms' sub 100Hz bass profiles, an iOS device-measured FFT analysis profiles surprisingly similar signatures.

My 2nd system is in a 12' x 22' space, on the narrow wall, but like the 1st, it is not fully bounded in an open plan house. That room presents different anomalies, none of which are practical nor actionable to treat. And anyway, that is a relatively near-field setup.

So net is, in rectangular rooms, I won't do anything acoustically that can't be mitigated by normal furnishings. If I had the severity of Keith's primary problem, I'd do the least needed to correct the 1st order acoustic dysfunction and live with the rest. Keith's room doesn't sound as bass-deficient nor as soft on the top end as it measures, and mine doesn't sound as bass-emphasized as it measures. What others do is up to them, but again, I don't advocate dedicated listening rooms. And I haven't heard one yet in 40 years of being exposed to them, that sounds natural enough to justify the work or the livability compromises. The best domestic room I ever heard remains that beautiful space in an Arlington house, so whenever I consider a move to a new domicile, I just look for as many attributes of that space as I can get. Anyway, there are guitars that need buying and playing, too.

Phil

Charles, I had the good fortune of buying a house with an unfinished basement and thus my dream of an engineered room from the ground up has been realized. It is not your typical room with panels and bass traps. The actual walls have been mechanically grounded (ala Starsound/Sistrum technologies). The end stage has been realized when my neighbor's Best Buy grade system sounded more engaging than my big rig.

Agear,
Congratulations on your sucessful results. Do you plan to post your system and pictures on this site?I`d love to see that.
Regards,