VAC - any comments? Good or bad.

Just can't let this one go. What were you measuring? The amp output, or the speaker output in the room? What techniques, etc. Just curious. I spoke to Kevin Hayes personally, after this came up. Kevin is honest, sincere (doesn't mean he couldn't make a klunker) and he is nonplussed by this 'measurement'. So I really don't think unexplained 'scientific' measurements are as compelling as Subaruguru might think. I would like to know more about his process. I am very curious. If someone takes a manufacturer to task, it only seems fair to publish the whole of the technique involved in the 'negative' measurements he obtained.
Also, I would say that, if the Amp measures, independently, this poorly, it SHOULD be published, and the manufacturer, scolded. I do know that the Avatar will play the THIEL 3.6, (a speaker known for its horrific load, and inefficiency)quite loudly, and according to all reports, reasonably flatly in its output.
Again, very interested, and hoping for fairness on both sides.
Larry

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!

Larry. I threw out ALL my files save for those pertinent to gear I acually own, BUT I did keep some of the sets of measurements pertinent here, buried in a file of N803 vs Fidelio measurements, as it was the Fidelios that I used, not the Parsifal Encores, which weren't purchased until a month later, as I see my graphs are dated April 22, 2000....
I don't know how to plot curves in this space, nor how how to post and refer, so I'll just list calculated DIFFERENCE data between two pairs of test runs. The first string lists the differences in dB when going from the Audio Refinement Complete Integrated to the AVATAR, adjusted for equal pinks, rounded to nearest easy fraction (when read visually), and then to nearest typable decimal for your reading....The second string of data is similar, except showing a second test run REPEATING the AVATAR again, but with an NAD 7400 amp in comparison. The index is frequency.
If you plot the two curves, you will see quite remarkable agreement....If you then take the "difference of the differences" data to evaluate method imprecision among other
info note the otherwise randomness and smallness of the noise (indicating the relatively high confidence level of
my conclusions), and perhaps the wildness shown in the top octave. However, looking back at my raw data, I see that the original SPL levels of ALL data entry pairs for both test runs for the ARC and the NAD amps were within +/-1dB across the whole band! So it's clear that the variability is due to some inherent behavior of the Avatar....
Once you plot the curves (a picture's worth a thousand words here, guys 'n gals, so PLEASE...), you'll notice an interesting old "west coast" u-shaped curve, with a pronounced, wide dip starting at 100Hz, bottoming at 250Hz, and then starting a long climb back to reference at about 2kHz. The bigger problem is that this climb continues into a sharp spike at 4-5kHz, then tumbling fiercely into the ravine -15dB down at 12k! That it wildly rebounds past unity at 20kHz is also of interest....That this behavior was repeated in a separate test when compared to another amplifier later is of course important. (If the acoustic results were simply a u-shaped curve then of course one could just increase the gain a bit to bring the mids up, and thus enjoy a plumper bottom and bright top, referring to the amp as one with a warm bottom, recessed mids and a bright top. But the trampolining between 1k and up belies categorization nor acceptablility.)
I also ran several additional sweeps more casually, noting that other than a gain difference of 1.16dB, the triode and ultralinear modes acted similarly. It should also be noted that I did NOT plot response below 40Hz, as it was not of interest, and the Fidelios were set up too far out into the room to have sufficient boundary support to have adequate output below 50Hz........................................................Freq:ARC to VAC diff/NAD to VAC diff: 50Hz:-1dB/-1dB 63:-1/0 80:-0.67/0 100:-1.67/-1.33 125:-2/-2.33 160:-2.33/-2.67 200:-2/-2.33 250:-2.67/-3.33 315:-1.33/-2.5 400:-2.25/-1.67 500:-1.5/-2.5 630:-2/-2 800:-1.25/-1.5 1k:-1/-1.25 1.25k:-0.5/-0.5 1.6k:0/-0.25 2k:+1/0 2.5k:+1.25/+0.5 3.15k:+1.5/+1.25 4k:+2.67/3 5k:+3.25/2.33 6.3k:+1.25/+1 8k:-2.67/-4.67 10k:-7.67/-10 12.5k:-10.33/-12 16k:-5.33/-3 20k: +6.33/+2.67 (Phew!)
Difference data: test 1 minus test 2:
0 -1 -0.67 -0.33 +0.33 +0.33 +0.33 +0.67 +1.17 +0.6 +1 0 +0.25 +0.25 0 +0.25 1 +0.75 +0.25 -0.33 +0.9 +0.25 +2 +2.67 +1.67 -2.67 +3.67!
Further, the very high Q of the data above 6kHz suggests that a finer source of tests signals (1/6 or 1/10 octave warbles) would have been most beneficial to assess this apparent unruly behavior..............................................................................................................
So what do you think's going on guys? VAC had no additional response after I sent them the actual data and curves three years ago. The responses below 3kHz can almost be lived with in the old pulled-back-mids style, but I've never seen anybody's "simulated performance with a real speaker load" curve look this bad. And yes, BOTH channels driven simultaneously, so I doubt that it wasn't one side oscillating wildly or anything obvious. All tubes glowed equally in pairs, etc. And again, triode = ultralinear except for 1+dB gain. So I'm stuck here, hearing only wonderful things about VAC and its pricipals, but having only experienced the behavior noted above with the one product I spent much time with. Again, they redesigned this Avatar, right?

I think everyone who reads this can draw their own conclusions as to what was actually measured here.
The amplifier's real output is not measurable through a non calibrated loudspeaker, with further room calibrations made, to compensate for room, frequency anomolies.
If this measurement of the "amp" were taken with a million speakers, we would see a million different results.
I thought, when I read this that the, so called, 'amplifier measurements' were suspect, now I, and everyone can see what has happened. Poor Kevin, he must be pulling his hair out.
Good listening,
Larry

The ARC and NAD were shown to have only +/- 1dB across the whole band? PUULEASE.....this whole set of test measurements is just plain FLAWED. I say you stick to just listening to your system. ; )