I believe both of these have been reviewed in your magazine. Can someone please compare / contrast the sonic attributes of these amplifiers? How can an amplifier function without an output transformer?
What comes to mind is to ask your question about the lack of an output transformer on a vacuum tube amplifier to Ralph Karsten ... the president and designer of the Atma-Sphere brand of amplifiers and preamps. Anything that I could tell you about it would be a lesser version than coming from him despite that I know the basics of it. Perhaps actually call him and ask him. He is very personable and is willing to educate someone while being respectful of you in not trying to solicit your business at the time.
The majority of information you are seeking can be found on the Atma-Sphere website, specifically in the "Papers" area.
The MA-2 amplifier can handle just about any speaker load, due to the number of output tubes which operate in parallel to lower the output impedance.
In addition to auditioning the respective amplifiers, you may find it very useful to investigate anticipated maintenance of each, including estimated tube life and tube replacement costs.
Atma-Sphere dealer disclaimer.
Essential Audio ~ Chicago area ~ 773-809-HIFI (4434)
But how are the sounds of the two amps different?
I am sure the guys who make and sell these are "nice". But I really want to hear from the editors. I know these amps were listened to and reviewed by the people who run this site. I know there is a technical editor who knows what's going on.
What's the point of having this site if they don't contribute? I hope they are on vacation.
Why not trust your own ears?
Unfortunately, SundayNiagara is correct. There may be a dozen people in the entire world who have had these in their systems, if that. (Any way TAS can change their editorial policy to pass these goodies around?) So ultimately, you will have to listen to both to decide.
However, here are some things that may help you get a sense of their sonic signatures. I have heard ARC many times, but not the 610T yet. Generally, ARC sound very SS like with a bit tube naturalness in the midrange. I imagine the midrange in that amp will be amazing. JV is a most gifted writer, so see if you can get your hands on his 610T review, he is much more eloquent than I am!
I had the Atma MA 1 on my ML Spire system. It was BY THE BEST I HAVE HEARD Logans sound. People talk about power cables removing a layer of grunge. This amp removed a concrete wall! I had Ray Charles and Ella Fitzgerald returning from the dead and in my room, it was so real. On my Soundlabs, however, which are probably a similar load to your Prodigies, the MA1's sounded fabulous and 3-d on the midrange, but did not have enough juice to reproduce faithful highs or bass. The dynamics and panel control was lacking. If you do hear the MA2, I would love to hear your thoughts.
Also, if you are auditioning at this level, you should probably hear the big VTL's also. VTL, out of all tube companies, probably has the best bass. And bass is the foundation of music...
I guess I am one of the few reviewers who has reviewed both the MA-2 and 610T, although the version of the MA-2 that I reviewed almost a decade ago was not the most current version and I've never actually compared the MA-2 to the 610T, although I did compare it directly to the REF300. At the time I think I was using SoundLab M-1s, Pipedreams, Avantgarde Trios, and Shun Mook Bella Voces as references.
I believe I actually made the comparison to the ARC REF300 in the review, but as I recall the difference between the two amps boiled down to the difference between OTL Class A triode sound and push-pull Class AB pentode sound. The Atma-Sphere triodes had tighter image focus, richer (denser, darker) tone color, better transient response, better grip in the bass, lower grain (particularly in the upper mids) and hence higher "liquidity," and an overall balance that was weighted more from the midrange down (i.e., a darker balance), The ARC sounded altogether bigger, bloomier, airier, lighter, with less tight-fisted "control" in every area, an overall balance that was weighted from midrange up (i.e., brighter), and more of what I call "action" (which is the sense that an instrument or a voice is not just beaming its energy at you like a flashlight but projecting its energy three-dimensionally like a lightbulb). The ARC was not as dense in tone color, as low in grain, or as downright "beautiful-sounding" as the Atma-Sphere, but I did love its bloom and air and action, which I thought were very realistic.
Although the 610T is a BIG improvement over the REF300 (and I'm sure the latest version of the MA-2 is considerably better than the earlier version I tested), I'd imagine that some of these differences in presentation will have remained the same. Without question, they are both great tube amps. As Sunday rightly said, which you will prefer depends almost entirely on you--the music you listen to, the levels you listen at, the other equipment you listen with, and, of course, the kind of sound that you think of as "lifelike" or "accurate" or "pleasing" or all three.