I'm not clear at all as to what assumptions I've been making? That you haven't listened to the LTA you measured? If you have listened, why be mysteriously silent about it? And if so, I expect double blind...
I understand that the orthodoxy here holds that an amp must be a vehicle of an ideal transparency and that this ideal can and will be revealed to the amp designer through measurements. While I have no tech background to comment with first hand experience, I did do a quick search for comments from a couple of well known amp designers which, to me anyway, show a nuanced approach:
Bruno Pultzey on discovering how drastically increasing negative feedback smooths distortion and that the result is... it sounds good:
"...if you take a simple amplifier which has acceptable distortion (just a second harmonic is what I use as an example) and you start applying feedback, harmonics will appear that were not there originally. Higher-order harmonics, even and odd, turn up out of the blue. So if you apply a little bit of feedback, the second harmonic that you wanted to reduce drops by a little, but out of the blue you get this whole smattering of high harmonics. It is quite understandable that this doesn’t sound good. That observation has been made and published by various people over the years, but the most important conclusion was never drawn: If you keep increasing feedback, if you turn the feedback knob up and up and up, you quickly hit a point where those distortion products all start coming down again and the signal does start getting cleaner. And if you get to very large amounts of feedback, the result is just supersmooth. So that is why I say that it is normal for an experimenter to experience that if you take a good-sounding zero-feedback amplifier and add 6dB of feedback, the result sounds worse. They heard that right. But had they been in a position to add 60dB, well then, suddenly they would have been confronted with a sound that is little short of magical."
On how measurements are his focus, but recognizing that subjective listening acts as a guide
"I very often have to invent new measurements on the fly when I suspect there might be something going on that doesn’t show up clearly on standard measurements."
" You calibrate by ear your set of measurements and the methods by which you measure, but you optimize your circuit by measurement. That is much more logical. You should take science to the absolute limit and crosscheck your scientific, technical procedures with what you are hearing, to make sure you’re not forgetting anything. The purely technical road in the end will yield a circuit that really sounds better than what you can get by mere philosophy and tuning parts."
John Curl, similarly to Pultzey, on hearing being a guide to discovering more revealing measurements:
"While mylars are fairly efficient from a size and cost point of view, we realized they have problems with dielectric absorption. I didn’t believe it at first. I was working with Noel Lee and a company called Symmetry. We designed this crossover and I specified these one microfarad Mylar caps. Noel kept saying he could 'hear the caps' and I thought he was crazy. Its performance was better than aluminum or tantalum electrolytics, and I couldn’t measure anything wrong with my Sound Technology distortion analyzer. So what was I to complain about?
Finally I stopped measuring and started listening, and I realized that the capacitor did have a fundamental flaw. This is were the ear has it all over test equipment. The test equipment is almost always brought on line
to actually measure problems the ear hears. So we’re always working in reverse. If we do hear something and we can’t measure it then we try to find ways to measure what we hear. In the end we invariably find a measurement that matches what the ear hears and it becomes very obvious to everybody."
Nelson Pass:
"Measurements and listening go hand in hand. There is a correlation between objective and subjective, but they're not strictly causal relationships. Clearly, there are some amplifiers that measure great with "standard" measurements but don't sound so good, and there are examples of good-sounding/bad-measuring as well. The discrepancies are interesting because they point to either things that have not been measured—more likely, misinterpreted—or aspects of perception and taste that don't correlate to measured flaws. Or both.
Pass on amps having a sound signature:
"Fundamentally, what interests me most about amplifiers are the differences in sound created by different topologies and the characteristics of the active gain devices. There are few things I enjoy so much as to contemplate the specific (and complex) characteristics of the many transistors (or tubes) and how they might fit into an amplifier to deliver a sound which has a particular signature. Toward that end, I like simple circuits, partly because well-designed, simple amplifiers tend to sound better, and also because they bring the part's personality into sharper relief."
In closing, it seems logical to me that any amp, however transparent or low in distortion is going to have a sound signature when the signal is transduced by speakers. It strikes me as narrow to call an amp that adds some 2nd order harmonic distortion -- particularly when designed, for example, to a particular class of speaker (ie high efficiency) -- an "effects box" ----particularly when one has not listened to said effects box-- (to beat a horse, again-- sorry)
