Hears what JA had to say in Stereophile.. The Audio Research Reference 75 measures well for a classic tube amplifier design with a single pair of output tubes for each channel and a modest degree of loop negative feedback. Its output transformers are also of good quality, the only proviso being that the amplifier should not be used with loudspeakers whose impedance drops significantly below the nominal value of the output transformer tapI lack 99% of your engineering expertise, but I don't read the measurements as being as bad as you seemingly do. It seems to me that JA has a tendency to disagree with his own reviewer's perceptions as to which output tap is best rather than criticizing the design of this amp and it's output tap measurements per se. In some ways, this entire discussion is premised upon design expectations; should the amp designer account for every possibility or to some degree, is the end-user responsible for matching the amp to a suitable loudspeaker? It seems to me that you adopt the former view, which is somewhat quizzical given your avowed distaste for dynamic coned speakers and your view that ESLs/Planars are the only form of speaker that makes musical sense. For better or worse, at Stereophile high-dollar tubed amps seem to be always matched up with various iterations of Wilsons, none of which present graceful impedance curves. I find it curious in general, Roger, that you defend measurements of tube amps as meritorious in a vacuum (pun intended). You seem to imply that the measurements may not tell the complete story, but that just the same any mediocrity in the measurements that are utilized is sure to correlate with deficiencies in sound. In other words, I interpret your posts-not just in this thread but in others too-to be consistent with a person who adopts only the first half of the golden oldie phrase, "not all things that count can be measured and not all things that can be measured count".
Read more at https://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements#jbpCd1H...
This may dismay you quite a bit from an engineering standpoint, but I take measurements of tube amps to be very analogous to measurements of DAC's; the best measuring DAC's don't often sound the best. They don't even necessarily render the so-called "musical truth" the best. Is there a known measurement of tubed gear that can predict a tube amp's ability to render the texture of a violin or the blat of a trumpet, the subtlety of David Rawling's plucking of a Martin acoustic, let alone sound stage width or depth?
I do agree with you that for the price charged, ARC has no excuse for mounting tube sockets directly onto the PCB. But to my knowledge, that is a reliability issue and not a performance issue. I also agree with you that ARC gear is unnecessarily complex and hard to service. The same could be said for BAT and Lamm and yet they have great reputations. The sheer number of capacitors in both my ARC Ref 150SE and Ref 6 is either alarming or impressive depending upon one's point of view. Again, BAT and Lamm seem to adopt the same approach.
Your own decision to go hybrid with your higher powered amp and to go true balanced with your higher powered amp but not your lowered power amp is a head-scratcher. If-as you state-monos are more susceptible to hum than stereo amps, why do you implement RCA-only vs. offering true balanced in the opposite direction? And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn't it indisputable that it is cheaper to produce and less complicated? You on the one hand have little good to say about Rogue and yet when it comes to hybrid tube amps, I think of Rogue (and Musical Fidelity though I don't count their "tubes" as tubes).
