Hi Larry, et al.
I don't have the actual response data I estimated above at hand, but I did publish it in an audioreview.com (or whatever they're called) review last year or so), and can probably retrieve it somewhere, unless I through it out during an annual office-cleaning last winter. I didn't buy the amp, so there was no reason to keep an old file.
But the methodology's what's important here, and has been used by me several hundred times throughout speaker and crossover design, so that's implanted in my brain:
Radio Shack SPL analogue meter, at listening ear height, just in front of listening position, which is just about configuring a 7.5 foot equilateral triangle, with, in this case, pair of Verity Audio Parsifal Encores.
Sturdy tripod is used, of course, and NEVER moved even 1/8" throughout all trials! (Some of you will know how important this is for measurements in the midband.)
1/3 octave warbles sourced from Stereophiles test discs, as they're convenient, and played on EMC-1 CDP, through Aleph P pre and Aleph 2 monos, through Nordost SPM/RedDawn XLR,and Red Dawn cables. Room is heavily damped, including first reflection points.
Comparison amps included: Acurus whatever $1600 ss amp, Audio Refinement Complete, NAD 7400 (receiver), and of course the Alephs now in place.
Procedure: Streophile disc plays 1/3 octave warbles 200Hz down to 20Hz, then 250Hz up to 20kHz. Full 20-20kHz plots were run for each amplifier. The order being one of the ss first, then the Avatar, then another ss, then the Avatar again, then another ss.
Results: all ss agreed within 1/4-1/2dB across ALL test warbles! Both Avatar curves self-agreed within 1/3-1/4 dB (test self-noise limit given by SPL meter readability, and imprecision limit in midband, as extra care required to NOT move human head).
Again, the difference in non-linearity between the AVATAR and the three near-clone ss amps was VERY HIGH in signal/noise ratio. Now you could say that the AVATAR was right, and the three ss amps were wrong, because the Radio Shack SPL meter is itself not very linear. But listening tests with the AVATAR certainly indicated that many things wre completely wrong, and easily correlated with the data:
the bloated bass, the recessed lower mids, the big peak in the low treble, the severely depressed upper treble.
Finally I obtained the Aleph P and 2 monos, which of course measure like the ss amps, but sound glorious.
FYI. The Parsifal Encores use a 4 ohm woofer, but are said to provide a near-constant impedence load that's easy to drive, albeit not as high in impedence as the original Parsifal using an 8 ohm woofer. I would imagine that the very high output impedence of the AVATAR has trouble with any 4 ohm driver, but again, the amplitude of the deviations I observed, and several of us heard, were shocking. "Kind of Blue", even in cleaned up latest form, was screechily unlistenable! Yes, I was told by VAC to try out their 90-90 or something like that (70?) as an example of a truly linear amp, as they too expressed concern over the unruliness of the output impedence of the tubes used in the Avatar. I'll try to find the audioreview.com review data to the difference plot can be drawn. I wasn't making a mountain out of a molehill here. +/- 1-2dB I was expecting, but 3+ makes a joke of the speaker designer's art!
