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Home Theater Shack 2015 High-End Amplifier Evaluation Event Reporting and Discussion Thread

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#1 ·
Home Theater Shack 2015 High-End Amplifier Evaluation Event Reporting and Discussion Thread



:fireworks2:
:fireworks1:




This thread is a continuation of the High-End Amplifier Evaluation Event Preparations Thread previously under way.



The event has begun. Coming to you from southern Alabama, the Home Theater Shack Evaluation Team has assembled at Sonnie Parker's Cedar Creek Cinema for the 2015 High-End Amplifier Evaluation Event. We have amps, we have speakers, we have tunes, we have great eats, what more could one ask for?

Be reminded of the first law of audio evaluation event execution. They never go exactly as planned. Not everything gets there, not everything works, but you endeavor to persevere and get things done.

We have deal with speakers not able to reach us in time, with cabling issues, with equipment not interfacing properly, a laptop crash, with hums and buzzes and clicks and pops, with procedural questions - - - yet we forge ahead, adapt, evolve, redirect, and forge ahead some more - - - and the task of evaluating amplifiers is underway.

Speakers: We were unable to get the Chane A5rx-c and the Acoustic Zen Crescendo Mk II speaker pairs. We are running the Spatial Hologram M1 Turbo v2 and the Martin Logan ESL. Both are very revealing speakers, baring a lot of inner detail in our recordings. They will serve us well. The A5rx-c will be reviewed for HTS when available.

At the moment, the Holograms are serving as our primary evaluation tool. I will post setup details and interesting discoveries a little later. They are giving us a monstrous soundstage, the kind that eats small animals for breakfast, with extremely sharp imaging and very good depth acuity. They are extremely clear, getting into the realm of rivaling electrostatic transparency. Their in-room response is very good, with some expected peaks and dips, but still very listenable. The high frequency response is extended and smooth. The bass gives you that "Are you sure the subs are not on?" feeling on deeper tracks.

We decided to start with sighted comparisons and open discussion today, and blind tests tomorrow. The Audyssey XT32 / Dirac Live comparison has not been completed yet.

Have we heard differences? Yes, some explainable and some not. One amp pairing yielded differences that several evaluators are convinced they could pick in a blind AB test.

One thing I have learned for sure: The perfect complement to good southern barbeque is a proper peach cobbler. Add great company and you have a perfect get-together.

The Event
  • Date: Thursday evening, March 12th through Saturday evening, March 14th.
  • Place: Cedar Creek Cinema, Alabama, hosted by Sonnie, Angie, and Gracie Parker.
  • Evaluation Panel: Joe Alexander (ALMFamily), Leonard Caillouet (lcaillo), Dennis Young (Tesseract), Sonnie Parker (Sonnie), Wayne Myers (AudiocRaver).

The Amplifiers
  • Behringer EP2500
  • Denon X5200 AVR
  • Emotiva XPA-2
  • Exposure 2010S
  • Krell Duo 175
  • Mark Levinson 532H
  • Parasound HALO A31
  • Pass Labs X250.5
  • Sunfire TGA-7401
  • Van Alstine Fet Valve 400R
  • Wyred 4 Sound ST-500 MK II
The Speakers
  • Spatial Hologram M1 Turbo v2, courtesy Clayton Shaw, Spatial Audio
  • Martin Logan ESL
Other key equipment special for the event:
  • Van Alstine ABX Switch Box, recently updated version (February 2015)
  • miniDSP nanoAVR DL, courtesy Tony Rouget, miniDSP
  • OPPO BDP-105

As mentioned, our deepest appreciation goes to Sonnie, Angie, and Gracie Parker, our hosts, for welcoming us into their home. Look up Southern Hospitality in your dictionary, and they are (or should be) listed as prime role models thereof.

This first posting will be updated with more info and results, so check back from time to time.




Amplifier Observations
These are the observations from our notes regarding what we heard that were supported by being consistent between sighted and blind testing and across reviewers. While we failed to identify the amps in ABX testing, the raw observations from the blind comparisons did correlate in some cases to the sighted observations and with the observations of other reviewers. Take these reports for what they are, very subjective assessments and impressions which may or may not be accurate.


Denon X5200 AVR

Compared to other amps, several observations were consistent. The Denon had somewhat higher sibilance, was a bit brighter, and while it had plenty of bass it was noted several times to lack definition found in other amps. At high levels, it did seem to strain a bit more than the other amps, which is expected for an AVR compared to some of the much larger amps. Several times it was noted by multiple reviewers that it had very good detail and presence, as well as revealing ambiance in the recordings.

We actually listened to the Denon more than any other amp, as it was in four of the blind comparisons. It was not reliably identified in general, so one could argue that it held its own quite well, compared to even the most expensive amps. The observations from the blind comparisons that had some common elements either between blind and sighted comparisons or between observers are below. The extra presence and slight lack of bass definition seem to be consistent observations of the Denon AVR, but everyone agreed that the differences were not a definitive advantage to any one amp that would lead us to not want to own or listen to another, so I think we can conclude that the Denon held its own and was a worthy amp to consider.

Compared to Behringer
- bass on Denon had more impact than Behr, vocals sounded muted on Behr
- vocals sounded muted on ML compared to Denon
- Denon: crisp highs preferred compared to Behringer which is silky.
- Denon is more present, forward in mids and highs than Behringer.

Compared to Mark Levinson
- Denon seemed to lack low end punch compared to ML.
- Denon is smooth, a certain PUSH in the bass notes, cellos & violins sounded distant, hi-hat stood out, distant vocal echo stood out, compared to ML.
- Denon bass seemed muddy compared to ML which is tighter.
- ML more distant strings than Denon.
- Denon is slightly mushy and fat in bass. String bass more defined on ML.
- ML seems recessed compared to Denon.

Compared to Pass
- vocals sounded muffled on Pass compared to Denon
- crisp bass on Denon compared to Pass
- Denon & Pass both even, accurate, transparent, natural, no difference, like both
- Pass seems soft on vocals but very close.
- Denon has a bit more punch on bottom, maybe not as much very deep bass, more mid bass.

Compared to Van Alstine
- bass on Chant track was crisp for VA while Denon was slightly sloppy
- sibilance not as pronounced on VA as it was on Denon
- VA super clarity & precision, detailed, space around strings, around everything compared to Denon which is not as clear, liked VA better.
- sibilanceon Denon, VA has less “air” but more listenable, both very good
- Very deep bass more defined on VA, overall more bass on Denon.


Wyred 4 Sound ST-500 MK II

In the sighted listening we compared the ST-500 MK II to the Van Alstine Fet Valve 400R. The assessments varied but were generally closer to no difference. The Van Alstine got comments of being fatter on the bottom. The Wyred 4 Sound was noted to have slightly better bass definition but apparently less impact there, and slightly less detail in the extreme highs. Most comments about the midrange were not much, if any difference. An interesting observation here was by Wayne, noting that he did not think he would be able to tell the difference in a blind comparison. Considering the ST-500 MK II is an ICE design and the Fet Valve 400R is a hybrid, we expected this to be one of the comparisons that would yield differences if any. As I am always concerned about expectation bias, this was one that I was particularly concerned with. Van Alstine is a personal favorite for a couple of us so I expected a clear preference for it to be present in the sighted comparison. I felt that the Wyred 4 Sound amp help its own with the much more expensive and likely to be favored VA.

In the blind comparisons, we compared the ST-500 MK II to the Emotiva XPA-2 and the Sunfire TGA-7401 in two separate sessions. Of course, in these sessions we had no idea what we were listening to until after all the listening was done. In the comparison to the Emotiva, some notes revealed not much difference and that these were two of the best sounding amps yet. The ST-500 MK II was noted to have the best midrange yet, along with the Emotiva. It was described as having less sibilance than both the Emotiva and Sunfire. Both the Emotiva and the ST-500 MK II were described as unstrained in terms of dynamics. In comparison to the Emotiva it was noted to have solid highs, lively dynamics, rich string tones, and punch in the bass. The overall preference in comparison to the Emo was either no difference to preferring the W4S.

In comparison to the Sunfire, comments ranged from preference for the W4S to not much difference to preference for the Sunfire. The Sunfire was described as having more presence in the midrange, while the Wyred was noted to be shrill, lifeless, and hollow by comparison.

These comments varied a lot, but the points of convergence were generally around the similarities to three amps that would be expected to be most likely to be different, if we found any differences at all. The objective results is that we failed to identify the amp in ABX comparisons to two other much more expensive amplifiers. I would have to conclude that based on the results, the ST-500 MK II represents one of the best values and certainly should satisfy most listeners.​





Audyssey XT32 vs. Dirac Live Listening Comparison

Last year HTS published a review of a the miniDSP DDRC-22D, a two-channel Dirac Live Digital Room Correction (DRC) product. The review included a comparison to Audyssey XT. A number of readers requested a comparison of Dirac Live with Audyssey XT32. That comparison was recently completed during the Home Theater Shack High-End Amplifier Evaluation Event at Sonnie Parker's Cedar Creek Cinema in rural Alabama. This report provides the results of that comparison.

Go to the Audyssey XT32 vs. Dirac Live Listening Comparison Report and Discussion Thread.


Spatial Hologram M1 Turbo Speakers

I was very pleased with the Spatial Hologram M1 speakers we used for the amplifier evaluation, and felt that they more than fulfilled our needs. They did not become "gotta have them" items for any of the evaluators, although I had thoughts in that direction once or twice. But they were speakers we could easily ignore through the weekend. I mean this as a high complement. Never did an evaluator complain that the M1 speakers were "in the way" or "holding us back," and we were able to focus on the task at hand unhindered. That alone means a lot, and may say more about them than the rest of the review just completed.

Here is what they did for us:
  • Because of their high efficiency, amplifiers were not straining to deliver the volumes we called for. We could be confident that the amps were operating in their linear ranges and that if we heard a difference it was not due to an amp being overdriven.
  • The stretched-out soundstage opened up a lot of useful detail for us to consider in our evaluations. In discussing the soundstage at one point, there was a consensus that it might be stretched a little too far and might be "coming apart at the seams," showing some gaps, although this did not hinder our progress. My final assessment is that this was not the case, all due respect to the fine ears of the other evaluators. I elaborate on this point in the M1 Review.
  • They served well as a full-range all-passive speaker, able to reach deep and deliver 40 Hz frequencies with lots of clean "oomph," all without the need for DSP boosting and without subwoofer support.
I thoroughly enjoyed spending time with them, and wish to again thank Clayton Shaw of Spatial Audio for loaning them to us. A complete review of the M1 speakers has been posted.

Go to the Spatial Hologram M1 Turbo Version 2 Speaker Review.


A Soundstage Enhancement Experience

Sonnie's MartinLogan ESL hybrid electrostatics were set up very nicely when we arrived, so we avoided moving them through the weekend. There were some improvements made to the soundstage and imaging by way of treatments, and some interesting twists and turns along the way which turned out to be very informative.

I have documented the exercise in a separate post.

Go to the Soundstage Enhancement Experience thread.
 
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#126 ·
#127 ·
I took the long way driving back, finally arrived home late last night. Catching up on this thread and having a listen to my system. Thinking, I need... more... power.
 
#128 ·
Well how did you like see the beach for the first time in your life Dennis?

Thanks for starting that up Leonard... good to see at least something up from the testing. :T

I would like to note that we did not attempt to blind test the Krell with other amps because it had a hum/buzz when connected to the ABX box that we could not eliminate, despite fairly exhausted efforts (even attempted using a conditioner). It would have been a dead giveaway to easily identify... as all we had to do was pause the track, mute the sound, stop the music play, switch tracks, etc... the buzz was clearly evident during silence. HOWEVER... I am happy to report that connected directly to my system without the ABX box, the Krell did NOT exhibit any buzz/hum... so it was only when in-line with the ABX box. We were concerned that it may have been a faulty amp, but not so... at least not when connected via normal (most likely) system connection methods.
 
#136 ·
Well how did you like see the beach for the first time in your life Dennis?

It was great! Spent some time with family, then participated in the Spring Break celebration. The beach, Battleship Park and Memphis Beale St. were a few of several adventures I had on my return trip. Narrowly avoiding a four car pile up on the Missouri interstate, rushing from car to car checking the occupants (all OK) ended an eventful week. 2514 miles logged on the odometer when I returned home.

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Thanks for starting that up Leonard... good to see at least something up from the testing. :T
Oh, yeah, that's right... the amplifier thing!
 
#129 ·
It is a lot of data to sort out. Giving it context so that it is meaningful and perhaps useful is a challenge. I started with the Denon because we made the most comparisons in the blind testing. There are two big takeaways from what we experienced with it. First, because the guesses in ABX testing were incorrect more than correct, ABX methodology needs some work. The second is that there were some consistent observations about the Denon AVR among the reviewers in blind and sighted testing. This suggests that there may be something to identify in objective testing, but the differences were not of a nature that any of us would say would disqualify it from consideration sonically when choosing an amp. Other than perhaps being a little underpowered for high level listening, it was certainly in the ballpark with some very highly regarded amps.
 
#172 ·
#133 ·
Krell is a very good amplifier, how can you go from Krell super fan to being ready to dump it based on an amplifier listening party that hasn't even had the results report written yet ?
I have a 5 yr old Pioneer AVR.
Approximately 100 watts/ch.
It does not matter what the results of this event are, I am not going to run out and add an amp or replace the AVR in favor of something else.
If I had an amplifier between the AVR and the speakers ( be it a pro amp, Emotivia, Krell, McIntosh, Bryston, Parasound....) it would not matter what the results of this event are, I would not consider taking the amplifier out of the system or consider replacing it with something else.
Relax and take a breath, maybe get that power cord double cryo treated or send the speaker wires for a cryo bath to get your mind off the amplifier.
You were completely satisfied with the Krell, this event should not change that for you.
 
#134 ·
Certainly don't trust our ears... this is merely information for your reading pleasure and should not be relied upon to make a decision on what to keep in your system and/or what to purchase. Let your own ears be the judge. One thing I have learned is I can't trust other people's ears to determine what I prefer.
 
#138 ·
Excellent point and I think one that's undermined in the mainstream audio press. I believe many followers of these magazines put reviewers on a pedestal. Rather than trust their own ears, they unquestionably follow their heroes. Companies have both profited from good reviews and suffered from bad ones.

In any case, Sonnie, congrats to you and the other reviewers (once again!) for keeping us aware of the pitfalls of comparison reports and reviews in general.
 
#135 ·
Ha... NO I am completely happy with the Krell. So far the music sounds great.... albeit the Ultras are a tad bass heavy even plugged.

The only thing I want to do is test is all. You guys only "sparked" my interest and I don't believe anyone but my own results....

I need to test for myself. End of story. This is why I spend so much $ in my camera hobby... I buy multiple lenses to test them and come to my OWN conclusion.

The ONLY thing this amp review has done is opened my "mind" to be more non Krell ony type attitude. I'll admit I was a big hung up on the Krell because it's my first real "amp" from a sorta respectable level. I was giddy.

Now... I want to back those claims with my own testing. Been looking at a few options here lately.

Ultimately I need to treat my room first to help my ears out first. BUT in the end... I do appreciate all of the hard work everyone that had participated in this event. Thanks!
 
#156 ·
I am waiting to release more on April 1 to keep everyone off balance, guessing whether the results are ficticious or not...

Seriously, no, we won't be publishing any April fool's day nonsense reviews. I would not want to be doing reviews at Sonnies on that date, however, being the jokester that he is.

What I am attempting to do is tease out of a lot of statistically insignificant data any meaningful comparisons and observations. Now that likely drives any researchers who rely strictly on "objective" statistical inference quite crazy, but it is the reality of our hobby. We have a combination of lots of objective data and subjective assessments. Looking at all of the sweep and impulse response data, and trying to correlate it to the observations of 4 listenters across more than a dozen comparisons, under two kinds of conditions, for 11 amplifiers, well, it would make for a multivariate nighmare if the data was just numerical. But this is much worse...

Combine all that with trying to wordsmith it all to make sure that people are least likely to take it out of context and be unfair to any particular product, and I have tossed a number of ideas that I had.

I am working on it all, and will be giving a summary of what we can say fairly about each of the amps. Just framing the question as "are there differences" is really not very useful, but I think everyone doing the listening would agree that they were all much more similar than different, and as we have all said, under the right power and listening constraints, they all do a great job and not one would be products that we would rush to sell if we owned it, nor would we hesitate to want to listen to any of them.

Wayne said in preface to his review, and I could not say it better, "The most important decisions about making a product or technology comparison are determining just what you are actually comparing and exactly how to make a fair apples-to-apples comparison. It is not always as easy as you might think it should be. I am convinced that most casual comparisons made between products are fraught with unaccounted-for variables, and are therefore flawed."
 
#158 ·
Meh, pretty sure if you brought a brand new fresh out of the box amplifier into a well established system and listening environment and did a blind A/B listening test against the very well known amplifier less than 1% of the system owners would be able to discern a difference.
Test could be repeated over and over for months and get the same random results.
If any particular individual falls into that super hearing group that ability must never be divulged to their wife because it would wipe out his ability to not hear her sometimes (if it's a woman her hubby can be told because wives hear everything even when we wish they couldn't) .
 
#159 ·
I will soon have quiet fans installed in my Crown power amp and, along with the Oppo HA-1 acting as DAC + volume control, will be able to perform long-term listening comparisons between it and my Onkyo TX-SR705 receiver driving my MartinLogan ESL speakers. Both will receive optical input from my music server.

Which intention should I prime my mind with as I begin that exercise?
  1. "They are different amplifiers, so they must sound different, so I will find a way to hear that difference."
  2. "All amplifiers sound the same so I will not hear a difference."
  3. "If there is a difference, I will hear it, if there is none, I will not."
  4. "I do not really care. If there is enough of a difference to matter to me, my brain will find a way to let me know."
  5. "Priming my brain with an intention beforehand is a silly notion, just enjoy the music and see what happens."
  6. "All that matters is that I will end up with a preference at some point, so that must be the better amp for me."
 
#160 ·
I'm sure I don't have to tell you this, but for others not picking up on it, you're comparing DACs and preamp stages in addition to amplifiers here. [Edit: unless, for the Onkyo, you're going into line-level multichannel inputs from the Oppo. Even then, you have the Onkyo's preamp circuit.] There will be those who will say that these things should be as transparent as amplifiers should be, but those who believe that amps can make a difference likely will also believe that the DAC and preamp circuits will also.

That said, I would go with the last option if you have a lot of time to compare. I haven't done a lot of this type of comparing, but it seems to me that if you're looking too hard for differences you may start to make them up in your head :coocoo:
 
#164 ·
I'm torn between #4 & #6:

"I do not really care. If there is enough of a difference to matter to me, my brain will find a way to let me know."
"All that matters is that I will end up with a preference at some point, so that must be the better amp for me."
Because in the grand sceme of things, all that matters is how we like the sound. What we already have as equiment currently...is our preference!
 
#168 ·
After some discussion with my uncle about this matter he said that even he would have some issues after listening to tons of music for durations that are full songs in length (i'm assuming fatigue?)

He mentioned the easiest way to tell and the only way he tests differences is keeping to only 3 tracks. One must be a natural string instrument like a violin or cello, the other must be a very well recorded live single mic track similiar to the Harry James recording and another is just whatever you want to use type thing, preferably something with a kick drum and/or horn he mentioned.

He went on saying that you MUST not listen longer than 1 minute of any of the 3 tracks. after a minute your brain is so complexly fooled that things get blended too easily. The way he explained it to me is with the complexity of acoustics hitting your ears that after one minute your brain will start ditching information.

1. 3 tracks only... same tracks... same media...
2. only the first minute
3. repeat that first minute with changes

This is how he told me he does it. He agree that fatigue destroys clarity.
 
#170 ·
The way he explained it to me is with the complexity of acoustics hitting your ears that after one minute your brain will start ditching information.
Your uncle is wise. It is auditory adaptability that tunes out the status quo (after a minute or so) so the auditory brain can be on the lookout for something new. It is looking for contrasts. It LIKES contrast. Which is why music contains phrases and movements and key changes and... And why A/B testing works so well.

This is a tendency, though, and can be overcome SOMEWHAT with training. How much? Nobody knows.
 
#174 ·
I have posted more detail in the comparison between the Denon AVR and the four amps with which it was compared in the Blind comparisons in the first post of this thread. All of the comments in the comparisons are observations from our reviewers in the blind testing, associated with the amp after the fact. The observations were about A & B, unknown to the listener at the time of the comments.

I have been over the measurements to find any correlations in the frequency response, impulse response, and distortion measures that would account for the observations that were consistent and found very little. There were slight differences in distortion and impulse response, but nothing that I would expect to account for the comments. The only significant frequency response anomoly was a slight roll off in response in the ML above 4K compared to the other amps. This was consistent with the observations.

The conclusions that I come to from all of the subjective observations in both blind and sighted conditions and the measurements confirm a few assumptions that I have been making for years. That, of course, could mean that those assumptions are justified, or that they color my assessment of the collected data. Judge that for yourself. It appears to me that because we had some consistent blind observations about some of the amp comparisons that there may be some differences that do exist that are very subtle and hard to identify in ABX testing. On the other hand, we did fail to identify the amps correctly in the ABX testing. Once again, we have a conflict between objective and subjective testing. What justifies some concern, IMNSHO, is that some of the blind observations were consistent and specific. I BELIEVE that future testing should focus on identifying observed differences and focus on extended listening with multiple trials to determine if they are, indeed, repeatable. It could be that what we observed that seemed to be consistent was simply chance. Regardless, if there are differences, they are very small, far less than many reviewers and vendors would lead us to believe. I think that this is a reasonable expectation. For those who want to extend that notion to say that there simply are no differences in amps, I have to say that you are justified in believing that. To those who argue the opposite, I would say that you, too, are justified in believing that, but you have to account for expectation bias, which, beyond any doubt, contributes to the significance attributed to any differences that are observed whether they are there or not. Once again, I take the middle road and probably don't satisfy either side. So be it, as the results here seem to justify my opinion that the correct answer is more complex than either side would like to admit.

I am working through the data in the other comparisons and will be publishing more, but the Denon was compared to 4 other amps, giving much more information and more opportunities to identify consistent observations. There won't be as much to report simply because it is more difficult to find consistency in single comparisons, but there are a few that stand out.
 
#180 · (Edited)
Denon was compared to 4 other amps
I think this is the paramount interest. Do we need external amps to drive our mains when it is set for 2 channel stereo? How does the SI&D compare between the two. How perceivable is the added headroom...enough to justify the expense?

So, not so much of "which amp" as it is "how much amp?"

I would expect the differences to be increased in the HT setting.
 
#176 ·
Agree, nice write up. Thanks for all the hard work so far in doing this.

Reading into all that has been said so far I personally think that the differences between amps is small at best, not night and day. So in my opinion you can say that as long as properly matched to the load of the speaker there is not enough difference to justify the cost of the big $$ amps.
 
#177 ·
Here are the frequency responses for the amps that were compared to the Denon, with the exception of the Behringer. For some reason I could not find it, but there were no noted meaningful differences at the time. I am sure we have it somewhere.

Note that the levels were matched carefully in each comparison, but there were slight differences between those pairs. I have matched the levels at 500Hz for this comparison.
 
#183 ·
Is that the response from the main listening position and at least in the ballpark of what people heard? I ask because, no offense, the response seems terrible. More than 15db difference between lows and highs, with mainly the highs just dropping like a cliff. And the huge 10db notch at 2k right where our ears are most sensitive.

I get that from a pure measurement difference things are all relative and shouldn't matter. I was thinking more from the subjective testing standpoint if this reflects what people were hearing.
 
#178 ·
If $$$$$ amplifiers bring a person pleasure they are worth it.
But if the goal is to spend as little $$$ as possible to get improvement in the audio it is difficult to make the case for spending $$ on outboard amplifier/wires/accessories when speakers make so much more difference in how the audio sounds.
When recommendations are asked for to get better sound quality outboard amplifiers should be far down the list most of the time.
 
#179 ·
I agree, Tony. The fact is, however, that many people DO experience differences that they find to be significant. It is real to them. What I believe these results indicate is that there are possibly differences that are audible, even if our measurements do not capture them. If we assume that SOME, even slight differences MIGHT exist, the only intellectually honest way to proceed is to try to find those that might be repeatable in objective testing. This requires identifying the most likely candidate differences, then arranging testing to facilitate identifying them without the possibility of chance influencing the results. Considering the experience of the testers here, more trials with fewer amps, more time with more breaks, and consistent passages repeatedly may be the way to go. The X option appears to be a confusing and difficult aspect of the testing. In the future I would devise a list of characteristics for each amp, then ask the listeners in blind comparisons to rate those repeatedly in randomized trials, rather than trying to rely on memory to match characteristics.

Again, the point, IMO, is to identify whether there are meaningful differences in a universe of infinite possibilities. If those identified differences are present, they should be repeatable, but we have to isolate those variables. The ABX testing obviously, based on our experience here, introduces other confounding variables.

Any time one is doing testing on something that involves human perception, isolating the variables it very difficult. This is clearly the case here.

Also, again, with all that said, we may still be talking about angels on the head of a pin in terms of the meaningfulness of any differences for most people. If you assume for a moment that the differences that we heard that MIGHT be real are, they still would not be meaningful to most people. They might to a handful of us, but even we were not impressed with the differences in terms of driving a decision to purchase, and we probably care more than all but a very small percentage of the buying public. This is really more of an academic exercise than one of usefulness to the majority of people, even those that buy very expensive amplifiers.
 
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