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 too expected only good things from my first use of a VAC amp, and lugged home a well-broken in VAC Avatar a few years ago. The long story is somewhere else posted. Suffice it to say that it's horrendously high output impedence wreaked havoc with my newly-aquired Parsifal Encores (which are VERY easy to drive, btw), with disturbances as much as
+/- 5dB across the spectrum, as finally carefully measured
against two reference amps. Horribly overripe mid-bass, a giant low treble peak and no upper treble "air" made all discs unlistenable. I faxed curves to VAC and was finally told that the inexpensive AVATAR's output tubes were famous for nonlinearity and unpredictable results with real speakers, and that if I wanted really fine performance I had to get their bigger amps. Sad to say the Audio Refinement Complete ($995) I had on hand absolutely trounced
the $3800 Avatar in both triode and pentode modes.
I then came to look as Stereophiles "predicted plot" of real performance with an 8 ohm load with glass amps once in awhile in JA's reviews, but NEVER saw one with swings of the amplitude I measured (and many of us heard) through that Avatar. And yes, both channels were the same, the tubes were ok, power output was correct, etc.
Glad their higher end stuff is more linear, and that they've recently completely redesigned the 'tar. |
Exactly! VAC's techie admitted that the EL-34 in the original AVATAR was quite unruly, though with the relatively benign imp curve of the Parsifal Encore I expected better linearity. As I remember the deviation:
Down a couple dB in lower bass, climbing to flat at about 60Hz, continuing to climb to maybe +3dB at 100, falling to a big trough at 250-400 or so, then climbing steeply to a BIG peak of about +5dB at 4k, then dropping ike a stone to -10k at 20k. Can you say screechy horns and bloated bass?
Whereas the three ss amps (NAD, Audio Refinement Complete, Aleph P+ 2s) agreed within +/- 0.25dB (meter/eyesight noise). Again, this is NOT a blanket disparagement of all VAC products. And although I know nothing of the new version of the Avatar, is it possible that they're using a more linear, predictable output stage with a much lower output impedence? Anybody know? I really felt badly for Julien Pelchat on the other end of the line in in Quebec when I told him what this amp was doing to his careful crossover work! Why bother to sweat driver matching and all that crossover research your design rests at the whim of unruly whipsawing? After I returned the AVATAR tyo the Pass/VAC/Verity/etc dealer he DID admit that it sounded different from all other amps. Phew.... |
Well, it's clear that Lrsky and Balekan don't understand the test. Once again, a reference test was devised using the same software (CD of 1/3 octave warble tones), CDP, cables, speaker/positioning/room, microphone/meter/battery/tripod/positioning/decade-selection, and operator eyes, with the ONLY VARIABLE being the choice of amplifier. Three ss amps and one VAC AVATAR were tested. The three ss amps agreed with each other so closely in ALL results that it is easily said that they grouped as a "standard" curve. The VAC AVATAR's responses were extraordinarily different. I posted the results of two of the test runs in a previous post above, noting only the DIFFERENCE DATA from the ss amp to the AVATAR in each of the two test runs.
LRSKY, Everyone CANNOT "draw there own conclusions as to actually what was measured here"! What were measured were in-room responses of total systems, identical except for the substitutions of amplifiers. The difference-data was then plotted as a curve. It should appear as a straight line of zero slope, as it does between any two of the ss amps. When any of the ss amps is compared with the AVATAR the difference surve is as provided above. What the original data curves are doesn't matter, and of course WOULD differ dramatically would a change in ANY item in the reference system chain...especially a transducer (speaker or the test microphone) and/or its positioning. That's why I took GREAT pains to assure matched tested conditions for each pair of sessions. (Even test meter battery strength was assured). So now you understand that NO claims of linearity can be made for ANY amp in this test, as there is no absolute reference for linearity. Granted. Of course. I don't care. Nobody does. My only attemt was to validate what I heard empirically: the VAC significantly changed the sound of the Verity Audio speakers, and much for the worse (IMO), compared to other amps I had on hand. I wanted to see if I could bear this out spectrally, and indeed the results are all too obvious.
So Larry, I trust you understand that I wasn't attempting to measure amplifier output on an absolute basis. It's unnecessary in this case. Differential testing is much easier and at least equally valid, as common biases are eliminated. My background is in test methodology, so give me a nod here....
Balekan, you too misunderstand. The ss amps agree with EACH OTHER within a dB across the band, not with any other reference axis. Again, the actual curves plotted are pretty wild messes that combine the speakers in-room with the pretty serious errors of the SPL meter. But I've gotten good enough at REPLICATING test runs with this setup to be able to tweak crossover designs in 1/3dB increments in the past, so it's been a pretty subtle differential tool.
As others who use similar setups know head-movements account for the greatest amount of the imprecision of the noise-floor. The ss amps all agreed well within +/- 1dB of EACH OTHER as a group, which allows a conclusion ofan "ss standard" for this test, if you will. The two VAC curves agreed quite well with each other, also (I didn't test p level, as it's only two sets of data), and the differences between this data and the ss "standard" is so large as to be very significant, and remarkably audible.
Again, if you plot out this "difference" curve as provided above (either one...they look the same), you can get a sense of the acoustic analogue (no pun).
L&B, I'm trying to think of a good example to explain to you the differential testing method I used. If you and your buddy are having a race it's unnecessary to know far or how fast both of you have run to know who's ahead; you just have to measure the distance between you.
This setup has been used innumerable times by speakerbuilders, especially, to tweak their designs. Again, there's almost no interest in the ACTUAL reference level against 0dB, but only in what happens when you tweak a cap or resistor on that tweeter, for example. You rerun the curve, and look for a subtle shift in the results, and plot the difference data. Same thing applies for testing amps...especially those with high enough output impedences that could actually change speaker output spectrally. Again, the amplitude of the distortion here is what is so shocking, and I imagine said non-linearity was probably one of the reasons for the redesign of this amp. I didn't mean for this chapter to ambush the thread, but it's clear that
L & B didn't understand the test methodology nor the validity of the results. Thanks. |
Lrsky, we're way past your suggestion. MANY manufacturers of audio components devise simplified controlled test methodologies to evaluate product tweaks and of course during ongoing manufacturing QC. You don't have to reinvent the wheel every time you want to look at a performance criterion. I spent a former professional life devising test methodology for laboratory equipment evaluation and manufacturing processes, culminating in chairing ASTM/ANSI and ISO subcommittees in the late 80s. The subsets centered around piston-operated volumetric-ware: not unlike tiny "tweeters" for liquids, currently used in all labs tosample, measure and move around small (1 uL - 1ml) aliquots of liquids hither and yon. You see these little pipettors (The "Pipetman" is the one I co-invented) on TV as reportes think they're camera-friendly for the general public....
The point is that there is NO DIRECT WAY to measure a uL of volume in a short amount of time! You have to rely on an indirect means, perhaps such as radiometrics, spectrophotometry, or im my developed expertise, gravimetry of water. By knowing a LOT about what happens when you move volumetrically and then weigh tiny amounts of water drops you can very noiselessly measure true volume. That's how nearly ALL the volumetric lab equipment in everly lab in the world was calibrated. And I wrote the friggin methodology. Now doing the ALL the reference measurements for imprecision and bias (barometric pressure, temperature, evaporative blanking, time-clock matching, microgram balance calibrating, operator bias calibrating (these are often hand-held devices), and a few I've plumb forgotten, for EACH string of measurements would be preposterously inefficient. Especially for $100-500 hand-tools. So manufacturers have devise highly-controlled procedures (or at least that's what my publications were supposed to teach them to do!) to shorten these "controls" to only several minutes per device. It was this kind of atmosphere in the late 80s in Geneva that spawned ISO9000/1/2etc. Unfortunately that's become more of a paper-cover set of machinatuions rather than necessarily a raising of quality level. But I digress.
It onlly takes a cursory reading of a few back issues of Speaker Builder et al to uncover manufacturers who've used simple SPL meters in real-world acoustic setups to uncover non-linearities in switched-component analyses via differential testing. I casually mentioned my testing to a chief designer (ex-KEF, now Boston Audio), as well an ex- BBN master acoustician, who implicitly trusted the soundness of matched-reference technique analysis for uncovering non-linearity of a suspected "unorthodox behavior of a gain device". Indeed, when I mentioned my results to VAC's folks, after a cursory description of technique, their concern was NOT my procedure, or its validity, but the degree of nonlinearity of the results, which they said again seemed surprising, even for the admittedly unruly output stage of the AVATAR.
So Lrsky, I kindly suggest that you step back a bit here, as my technical prowess as organizing a valid scientific inquiry is not truly in question...I've got the backing to pass ANY scrutiny of methodology despite not having conventional DIRECT high performance traditional electrical instrumentation, and please not be coy about summoning the industry gods to pass judgement on what anyone of reasonable facility with the scientific method can discern is a well-run set of differential tests. As well, the amplitude of the non-linearity difference to noise ratio is VERY high (although not calculated), so my experience tells me I'm on solid ground with the stat calcs too.
But again, rather than pee back at you, I'd rather educate.
What you simply do NOT understand is that calibrated speakers, room, mic, cable, etc., are NOT needed to run this type of test, as these items are held STABLE through all test runs. Repeat runs (controls) proved that system imprecision was extremely small (which I think you may not have a problem with); indeed the raw data is NOT flat in dB across the 27 or so test frequency points for any situation, because of ANY and ALL of the effects of the system. But they are STABLE as a rock (well within 0.5dB).
Again, the biggest sources of imprecicion are human headmovements and parallax error in eyesight.
This test can, and has been used validly by INNUMERABLE MANUFACTURERS to assess changes in one variable at a time at ANY component position in the system chain. I think that's part of what you don't get.... Whereas there is NO VALIDITY in quoting actual raw data in dB vs frequency because of no pure reference scale calibrations (that and efficiency are the reasons why I didn't post it); because of the stable RELATIVE REFERENCE, there can be great validity in concluding statistical significance from differential calculation of this "humpy data". |
Part II (Sorry!)
I guess another part of this is that manufacturers generally use resistive loads for amplifier measurement, wherein linearity usually appears reasonably flat. We're now used to seeing a curve now and again from some testers (like Atkinson at Stereophile) who throw in a "projected behaviour with an 8-ohm real speaker" curve, which, especially with a high output impedence amplifier, will show some non-linear frequency dependent behaviour.
In a way, there's some useful "single-blindness" in having very raw data. Indeed, after running the first SS1 vs VAC test, one can't tell by looking at the raw data anything.
I then ran the second test: SS2 vs VAC. A cursory examination of the two sets showed that SS1 very nearly equalled SS2, and that VAC very nearly equalled VAC. I then tried SS3 by itself, which equalled the two SS. The amplitude of difference between the VAC and the three SS was quite large (see the curves again), and correlated nicely with the gross differences in sound differences. Certainly the three SS amps had differences in sound, but these had to do with grittiness, edginess, decay, dimensionality, and all that typical SS stuff. The Audio refinement Complete Integrated clearly sounded the best. The Acurus and NAD I didn't like much. But ALL THREE SS AMPS sounded TIMBRALLY EQUAL, and indeed measured spectrally the same. It all makes sense. (Now do you understand, Balekan?) The three SS curves are very tight (intertest imprecision mainly given only by pink noise bias difference set by gain control). The two VAC curves are quite tight, only being a bit at variance at the 16k and 20k points where both are at highest slope, and therefore coarsest measurement...but also greatest non-linearity--quite wild rides....
The only almost-sily fly in the soup here is that someone could actually postulate that since the raw data is relative to an unknown (yet stable) reference base, isn't it possible that it's the VAC that is linear, and that the THREE SS AMPS are all wrong? Yup. Entirely possible. And if there was only one SS amp I'd have to agree, and would never have published these results. But when THREE different SS amps agree so highly, and one TUBE amp disagrees so greatly, TWICE, and sounds horrible, to boot, my money's on something terribly wrong with that output stage...when mated with the supposedly benign Fidelios. Ern |
Lrsky, you still don't get it! I have absolutely no axe to grind, DON'T OWN the bloody amp, and will try to answer your queries in order, as I flip back and forth: I used the terms "gods" because the suggestion that CEO's be called in to assess a simple differential test is technically naive. Any of the mentioned companies techs well-grounded in the scientific method would pass on the test without mention. Seriously. You simply do not see this. Secondly, the Verity Audio fidelio poses no unusual load whatsoever, being of fairly flat impedence with a 5.7ohm min, I think. But OF COURSE it's expected that the results would be different with a change in speaker IF the output impedence of the test amp was high. That's precusely the test's hypothesis! Why the bugaboo that the results simply prove convincingly that to be true? Again, changes in LOAD, and room loading, areinconsequential, as they are FIXED across all trials. Again, the basis for a differential series of test runs: only one variable (the amp) changes. Please try hard to understand the reasoning behind this. No condescension meant. It's critically important....Only one mic was used, so it's calibration is not of concern. Do you understand why? If not, I can explain later. Again, as the room anomolies remain FIXED, their effects are NOT of concern. Your dig was not necessary. I've TAUGHT more real scientists than you can count. No, I did NOT use more than one set of speakers (one per channel), because the point was NOT to investigate HOW the VAC varies with speaker load changes, which is another experiment requiring different test equipment. My test procedure was only to determine what the DIFFERENCE in frequency response was between the VAC AVATAR and the two SS amps I had on hand, as empirical audible evidence indicated a great discrepancy....No, I did NOT in any other way test the VAC beforehand, as it was a dealer demo, and naively trusted to perform normally. Both output halves matched, which seemed a rudimentary qualification, as well. It's not a customer's job to perform manufacturer's final QA. Yes, I'd rule out the 8' Nordost Red Dawn cables' very low inductance and resistance as significant contributants here. But that suggestion simply muddies the waters again! All system componentry (test equipment and conditions) were listed, unvaried, and NOT unusual in any way such as to skew freq resp between ss and valve amps, as most will agree....Again, I didn't "buy such flawed equipment", and thus didn't "lie in the bushes to ambush" anybody. I simply doubted what a gushing salesman who sold me Verity Audios told me about the Avatar, as my ears heard differently, so I tested it against two other amps in a very simle, but VERY VALID manner, and produced extremely significant results. Certainly NO-ONE has countered the methodology to date. A full list of the raw data is available to VAC as well anyone, although I doubt that anyone cares at this point, 4 yrs and a redesign of the amp later!...Again, why is my testing incomplete and imperfect, Lrsky? I remember back in the mid 80s I sat as the US rep on a Technical Advisory Group at ISO Tech Com 42 (Lab Equip) in Frankfort, where the DIN Secretariat lauded us for writing a standard that was efficient and tight, containing only what was "sufficient, but necessary". It was important him, as he had to organize translation into 17 languages for balloting. If I had tried to reinvent the wheel with every procedure we proposed in an ISO method we would never have gotten anything done! So sir, you may or may not be another Hemingway, but when it comes to running a simple differential test, please just trust that I know what the hell I'm doing. And I'm quite sure that a coffee mug can look like a red herring from certain clever angles, and necessarily so, as it's easier to shoot the messenger and leave the waters muddy, as you've done....
However, it IS true that NO ONE knows if the suspect AVATAR was working correctly when tested. I do remember that it sounded the same in BOTH channels, in both triode and pentode mode. So I continued like an ordinary consumer, trusting that it was a normally-functioning unit. It had ample output, too....
Lrsky, your last condescending remarks are is absurd, and perhaps psychological projection? I need ask no one if my testing methodology is valid. Chrissake, just take any college-level lab course and learn how to perform a one-variable test procedure. It's not alchemy! I've designed a couple of two-ways, and a three-way in the early 90s, using the same test setups to carefully tweak crossovers in 1/3 dB increments over 1 octave bands, thereafter learning you can't get a manufacturer to supply you with driver pairs matched well enough, and I didn'rt want to get into computer-matched pairs. I have GREAT respect for Verity, Snell, even Boston, et al, who control driver spec closely enough to make nice clones. I learned this from many years controlling production and QA of the world's most popular laboratory volumetric measurement equipment, called the Gilson "Pipetman". It's a handheld small volume auto-pipettor used down to 1 uL, calibrated by differential test methodology I developped in the 70s using gravimetry at the
1ug sens level. It's this stuff that I honed into ASTM and ISO standard procedures for calibrating volumetric ware so users in labs worldwide could test their pipettors, dilutors and dispensors inhouse efficiently instead of having to buy new ones, or, as you would prefer, Larsky, measure the room, all the beakers, and maybe the drapes too, and perhaps ask for permission before seeing if it's ok! Sigh...why the doubting Thomas?
Of late my semi-retirement and slipped disc has me still enjoying life in a third career as Boston's SubaruGuru, and as a contributor to this community, supplier of nifty $39 DIY all-Teflon PCKits that keep me in touch with a couple hundred of you guys....
Disgruntled? Hardly. Anti-audio? I've 50-60 cheap CD's I scooped up in Italy and at Heathrow this August I haven't even goten to yet. My two-ch ref system and my Steinway B are the aural delights of my life (plus frequent visits to Jordan and Symphony Halls). ANTI-audio? You been writing too much commercial copy? Re VAC, I have nothing but respect for a small successful company that manufactures great products. I've been self-employed for 20+ years. I have several friends whose small basement ops are now $5-8M music/audio companies, and believe me their noses are to the grindstone. I also just sold a Subie to the wife of the ex-production manager of one of them who, after 15 yrs, got sick of rushing product out the door to meet trade-show dates, brushing aside QA warnings. I wore BOTH those hats in the 70s and 80s at the same time, here in Boston AND in France; I know the stresses implicit when you've promised you'll never ship a product until it's perfect, and then you release a first batch, and then a second level tech finds a flaw two days later....
So yeah, it's easy to say that I got a bad AVATAR, or to incorrectly convince the naive that because I didn't calibrate a mic or measure the drapes my test is flawed, but that's all bull, and the congnoscenti know that. No axe to grind. I'm not into high output impedence tube amps. I tried ONE, May 2000. It went crazy on the VA Fidelio...sounded horrible. Freq resp was crap, as THREE SS amps self-agreed as a group. Here are the numbers: nice and valid. AVATAR since redesigned. Fine. Everybody's happy. 'Cept Lrsky. Why? |
TH, again perhaps the unit I borrowed was somehow seriously defective. FYI, output difference between triode abd ultralinear was +1.2 dB pink. That may or may not be a hint to VAC of whether this unit's performance was outlying the norms back in May 2000. Wish I had recorded the Serial No. for their attention.... The dealer (Ensemble in Arlington, MA) went belly-up in '02 as well, so tracing it seems difficult. Believe me, there was NOTHING neutral about this unit back in 2000. Glad you're happy. And if the Avatar is such a good circuit that it merited serious attention to upgrading with the result that VAC expects the market to laud it at $6k, then I trust that they know what they're doing, and hope that I simply happened to get a bum one.
But please, don't shoot the messenger nor his methodology.
Almost every biochem, analytical chem, microbio, virology, epidemiology, etc. lab in the country uses volumetric ware calibrated by "short-cut" procedures I honed and published in the 70's and 80's (that and a buck get's me HALF a cuppa...); so if you trust that your blood test comes back with some semblance of accuracy, or the cancer research at least seems to hold SOME sense of statistical promise for your mom's lump, please give me a bit of credit for somewhat creatively differentiating lousy performance in a specific horribly non-linear amp. Sorry for the wax job. |
