Solid State Preamp Reviews

Pass Laboratories XP-22 line preamplifier Measurements

Sidebar 3: Measurements

I measured the Pass Laboratories XP-22's performance with my Audio Precision SYS2722 system (see the January 2008 "As We See It"). The maximum gain was the specified 9.5dB for the balanced inputs to the balanced outputs, but 6.07dB from the unbalanced input to the unbalanced output, the latter result 3dB higher than the specified gain. The preamplifier preserved absolute polarity (ie, was non-inverting) with both balanced and unbalanced inputs and outputs. (Its XLR jacks are wired with pin 2 hot, the AES convention.)

The XP-22's unbalanced input impedance was close to specification at 20Hz and 1kHz, at 20.5k ohms, but a little lower at 20kHz, at 17.5k ohms. The balanced input impedance was twice the unbalanced, as expected. The unbalanced output impedance was 51 ohms at 20Hz, and 44 ohms at 1kHz and 20kHz. The balanced impedance was 44 ohms at 1kHz and 20kHz, and 65 ohms at 20Hz.

The preamplifier's balanced frequency response into high impedances was flat from 100Hz to 30kHz (fig.1, blue and red traces), though the low frequencies rolled off slightly into 600 ohms, reaching –1.5dB at 20Hz (cyan, magenta). Fig.1 was taken with the XP-22's volume control at its maximum setting of "99." At lower settings the ultrasonic output rolled off slightly faster, reaching –2dB at 90kHz with the control set to unity gain ("90"). Channel separation was superb, at >110dB in both directions below 4kHz, and decreasing only slightly, to 96dB, at 25kHz (not shown).

519PXP22fig1

Fig.1 Pass Labs XP-22, balanced frequency response with volume control set to "99" at 1V into: 100k ohms (left channel blue, right red), 600 ohms (left cyan, right magenta) (0.5dB/vertical div.).

From balanced inputs to balanced output, the Pass Labs preamp offered extremely low noise, with virtually no power-supply–related spuriae in its output, even with the preamplifier sitting atop its separate power supply (fig.2). From unbalanced inputs to unbalanced output, however, some spuriae crept into the spectrum at both the even- and odd-order harmonics of the 60Hz power-line frequency, even with the power supply sitting on the floor at the full length of the umbilical cord (fig.3). Even so, these spuriae were very low in level. The wideband, unweighted signal/noise ratio, measured with the unbalanced input shorted to ground but the volume control set to its maximum, was still 83.8dB ref. 1V output (average of both channels, which were very similar). Restricting the measurement bandwidth to the audioband increased the S/N to an excellent 85.35dB, while switching an A-weighting filter into circuit further improved this ratio, to 99dB.

519PXP22fig2

Fig.2 Pass Labs XP-22, balanced spectrum of 1kHz sinewave, DC–1kHz, at 1V into 100k ohms with: power supply on floor (left channel blue, right red), power supply under preamplifier (left green, right gray) (linear frequency scale).

519PXP22fig3

Fig.3 Pass Labs XP-22, unbalanced spectrum of 1kHz sinewave, DC–1kHz, at 1V into 100k ohms with power supply on floor (left channel blue, right red; linear frequency scale).

Fig.4 plots the percentage of THD+noise in the XP-22's balanced output into 100k ohms. The THD+N rises below 5V output due to the fixed level of noise becoming an increasing percentage of the signal level. The XP-22's balanced output doesn't clip (ie, when the THD+N reaches 1%) until 34V, which is almost an order of magnitude above the maximum level the preamplifier will be asked to deliver in typical use. As expected, the unbalanced output clipped at half this output level.

519PXP22fig4

Fig.4 Pass Labs XP-22, balanced distortion (%) vs 1kHz output voltage into 100k ohms.

To be sure that the reading was not dominated by noise, I measured how the XP-22's distortion changed with frequency at a very high level, 6V. The THD+N percentage was extremely low throughout the audioband into both 100k ohm and 600 ohm loads (fig.5), though with the usual rise in the top audio octaves. I looked at the spectrum of the distortion at a similarly high output level because, at 1V, no distortion harmonics were visible above the noise floor. The result is shown in fig.6; while the second and third harmonics can be seen, these are still at astonishingly low levels: below –100dB. Tested for intermodulation distortion with an equal mix of 19 and 20kHz tones at a more typical level of 2V, the second-order difference product at 1kHz was absent, and the higher-order products all lay at or below –97dB (0.0014%) (fig.7).

519PXP22fig5

Fig.5 Pass Labs XP-22, balanced distortion (%) vs frequency at 6V into: 100k ohms (left channel blue, right red), 600 ohms (left cyan, right magenta).

519PXP22fig6

Fig.6 Pass Labs XP-22, balanced spectrum of 50Hz sinewave, DC–1kHz, at 6V into 100k ohms (left channel blue, right red; linear frequency scale).

519PXP22fig7

Fig.7 Pass Labs XP-22, balanced HF intermodulation spectrum, DC–30kHz, 19+20kHz at 2V into 100k ohms (left channel blue, right red; linear frequency scale).

Like the other Pass Laboratories preamplifiers we've reviewed, the XP-22 offered superb measured performance.—John Atkinson

COMPANY INFO
Pass Laboratories Inc.
13395 New Airport Road, Suite G
Auburn, CA 95602
(530) 878-5350
www.passlabs.com
ARTICLE CONTENTS

COMMENTS
CG's picture
Submitted by CG on May 17, 2019 - 1:03pm

Personally, I don't know much about perception bias or any of that stuff. But, I do know a bit about engineering.

My own experience at my day job, which has nothing to do with audio, is that a lot of these little things that seemingly make no sense from a scientific perspective really do make sense once you dig deeply enough. There are lots of engineering design "rules" that are accepted as being perfectly fine but really are only ok, at best. When you examine very closely, you can not only find flaws through analysis but through actual measurement. The problem seems to be that nobody wants to go to that length, unless a problem pops up. (Think of the O-rings on the Space Shuttle.)

Here's a very simple example, having nothing to do with electronics.

Military snipers and guys who have to aim artillery weapons learned long ago that they have to take the rotation of the Earth into account, because the planet turns a small amount during the flight time of projectiles. People just tossing a football in the backyard don't need to worry about such things, and don't even notice, since there's other factors that dominate their throwing success. But, the Earth still turns, whether you notice it or not.

It's much easier to place the blame of a fault on somebody's perception. You have to wonder how many snipers and the like were chastised for being bad shots before the idea of Coriolis effect caught on.

But, to be really fair, people are moody, the air temperature changes as does the humidity and barometric pressure, and a zillion other things. So, personal observation may not be completely precise. That doesn't mean that it's dismissible. Just tossing off observations without taking everything into account isn't very scientific.

I'd also offer that almost every measurement I've ever seen for a piece of audio gear has been performed with the device under test in as much isolation from external influences as possible. That makes sense, except that these devices are never used that way. There are always interactions with other gear, but these get ignored. The only real test of a system is the listening test which is less controlled for the reasons stated earlier.

So, you have a funny dichotomy. The "objective" tests are performed not as the equipment is used. The "subjective" tests are performed as a system, but the results are less easily measured. Why is it that there are few or no attempts at rationalizing this?

Archimago's picture
Submitted by Archimago on May 17, 2019 - 2:50pm

"So, you have a funny dichotomy. The "objective" tests are performed not as the equipment is used. The "subjective" tests are performed as a system, but the results are less easily measured. Why is it that there are few or no attempts at rationalizing this?"

I agree, the dichotomy should not be there.

IMO, it's because the "pure subjectivists" don't believe in blind tests. So don't bother taking them and continues to make claims of massive differences! And then they find excuses why blind tests should not be trusted!

These days, it has gotten to the point where on some forums, talk of needing to do blind testing and the dreaded acronym "DBT" has become banned.

Whatever. Just do a blind test of that ethernet cable...

CG's picture
Submitted by CG on May 17, 2019 - 5:55pm

Personally, I have no use for the results of blind testing. Not that it's good or bad - that's not my complaint. It's that it doesn't help me get anywhere or make any progress. You've been very clear on your position in all this, as you routinely publish commentary on the topic. I'm not going to be critical of that nor say it's wrong. Or, right. Just that that's not a direction I wish to pursue or will travel.

I'm hardly a "pure subjectivist" by education, training, experience, career path, or in what I do in my own time. I am simply more interested in figuring out why something might sound better or worse. And, then doing something about it, at least when and where I can.

"Engineering" or "technical" testing would have been a better choice than "objective", because that was what I was really getting at. (However, I don't think that "objective" is the same as "objectivist" in this context) The limited measurements that are usually performed and the way they are performed are hardly representative of actual system performance. I mean that from a strictly technical point of view. It's just ironic that "subjective" reviews are the only ones that take system considerations into account.

So, my apologies for selecting the wrong term. That one really is on me.

michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 6:36am

We often hear the term "voicing" as part of the design process when manufacturing hifi products. For many designers, this is the final step (see the recent interview with Juergen Reiss of MBL on darko.audio).

This interests me, and is relevant here (I hope), for two reasons - it speaks to the fact that hifi products have a 'voice', and the only way to know what a given thing sounds like is to listen to it playing music in a system. Again, this coming from the people/engineers who actually make things.

If we were to apply the false (and forced) dichotomy of "Objective" v "Subjective" to this process, are we to believe that the people who make the gear don't know what they're doing? That the 'voice' designers speak of is nothing but a myth that can be easily dispelled by a few DBTs?

Of course, the suggestion is ridiculous. As ridiculous as believing that someone can determine how we will respond to a given component, speaker, or cable when playing music in a system based on measuring it in isolation.

Jim Austin's picture
Submitted by Jim Austin on May 19, 2019 - 9:15am
Michael, thanks for the comment. I'll just note that it may just be a difference of priority. "If I make it accurate," some say, "then it will sound as it should." There's still voicing, but it's a consequence of other priorities. Both approaches make assumptions that, on their face, are not justified. One assumes there are common principles that dictate appropriate sound*--beyond what one individual hears. The other assumes that what one individual hears will be heard by others; otherwise, what does 'voicing' even mean, and what's the point? * There actually is evidence to support this--statistical evidence at least. Jim
michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 10:21am

...a designer striving to hear from their gear, a sound that's in their head. At least this is the way I've had it explained to me by a number of designers.

I am familiar with some of the work Sean Olive has done at Harman and I'd imagine he would represent the "If I make it accurate." approach.

I also know an amp designer who doesn't listen at all. It is not a part of his process. The fact that I've found his amplifiers to be among my favorites is neither here nor there (but I do find it interesting).

What fascinates me most is this difference in approach. I am certainly in no position, nor will I ever be, to pick one as being best. Or even most correct.

Which gets us to what we, as listeners, are after and again there's no single answer that holds more weight than another. In my opinion, of course.

Thank you for taking the time to respond, Jim.

cgh's picture
Submitted by cgh on May 19, 2019 - 4:03pm

We do voicing in instrument building and I take it to mean the same thing in speaker design (with appropriate exchange of mechanical versus electrical analogues, art notwithstanding). For instance, we may string up a newly finished violin or guitar and take a little here and there off the bass bar or struts, respectively, after listening to notes in every register. Even before final assembly we may measure braced free plate spectrums or compliance and take 0.01mm-0.1mm of top thickness off.

Ortofan's picture
Submitted by Ortofan on May 19, 2019 - 11:18am

... "pleasant" versus "accurate" debate that David Hafler identified over thirty years ago?
https://www.stereophile.com/content/manufacturers-comment

Do you want your audio equipment to pass signals through it with as little change as possible, or do you want it to be "voiced" by adding helpings of what JA1 referred to as second harmonic "sauce", or whatever other modifications might make the resultant sound quality somehow more appealing to you?

michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 11:27am

With all due respect, this ‘choice’ you propose is unreasonably limited.

To answer your question, I want a hifi that allows me to listen to music as an activity unto itself for as long as I want.

Archimago's picture
Submitted by Archimago on May 19, 2019 - 10:19am

True Michael. There is of course many preferences that any listener will need to decide for themselves around "voicing"; especially of speakers.

But typically this is not what audiophiles argue about. It's whether for the money the box resonances demonstrated on measurements were really meant to be there. Or if a subjective reviewer says a new DAC is "awesome" yet it's clear that the noise floor is poor - was that "voicing" and intended? How about probably the most contentious of issues - amazing $10,000 cables that if one were to put in a test bench would show no difference compared to any other decent cable?

Beyond technical discussions and measurements, blind testing IMO is a useful technique both to keep oneself humble and "honest" (appreciating our own limitations as listeners), and also as a corporate exercise to determine whether something makes a difference for the majority of listeners. We might not bother with this for speaker "voicing", but we sure can to determine if supposedly neutral $10,000 cables, low noise $25,000 amplifiers and less jittery DACs have audible value when companies claim their more expensive devices are technically "better".

michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 10:40am

...because I mostly agree ;-)

Where we differ, and this is admittedly simply a question of approach and preference, is I do not feel the need to keep myself "humble" when picking out hifi gear and "honesty" doesn't even enter the picture. To clarify, I listen to music on the hifi for pleasure.

On the subject of cables and measurement, I would again point to Jurgen Reiss. I just listened to Jurgen's presentation in Munich on his approach to speaker design. He explained that he ships his speakers with three different wires for connecting the tweeter. Why? Because each wire, which are made of different materials, changes the overall sound of his speaker. The fun part is he has not been able to measure this difference.

"Value" is to my mind a very loaded term and best left up to the person doing the spending to determine.

Cheers.

CG's picture
Submitted by CG on May 19, 2019 - 1:11pm

After regaining consciousness in the aftermath of reading your post, a little light bulb turned on for me.

Back in the Jurassic days of audio and web publications, a guy who was as far from being a "pure subjectivist" as you can find authored an article as to why the typical measurements for cables used in audio systems were incomplete.

http://www.soundstagenetwork.com/articles/pete01.htm

I'm certain this information has been lost or plain ignored over the decades, as I suggested earlier.

His approach was also one that I think is worth considering. Take your observations and investigate as best you can what might be behind what you observed.

BTW, last time I communicated with Pete, he had punted audio altogether in favor of other hobbies.

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 1:21pm

Pete didn't do any DBT.

Didn't even consider it...

CG's picture
Submitted by CG on May 19, 2019 - 1:36pm

Never suggested he did.

His demonstrated approach - dunno what he was really thinking and I won't speak for him - appeared simple. He heard something. Then he set out to see why that might be. Then, if he could, do something about it.

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 1:58pm

He heard something...!

CG's picture
Submitted by CG on May 19, 2019 - 2:14pm

What a concept!

Archimago's picture
Submitted by Archimago on May 19, 2019 - 10:00am

"Personally, I have no use for the results of blind testing"?

Then what results do you "personally" find useful!? Is it really up to the "person" to decide? Does a person pick and choose what test was used to determine if the Earth is spherical or flat?

What better way than to literally have human subjects listen to playback of a full system and report whether something is audible while controlling for the inevitable psychological biases than blind testing?

No matter what technical or objective testing one does, you could always complain that the measurements used are "limited"!

The issue is that in audiophilia, there is an attempt to disregard the most powerful and relevant direct test there is! To continue doing this leads us round and again never knowing if subjective comments made have any relevance or truth at all.

CG's picture
Submitted by CG on May 19, 2019 - 11:31am

A couple points. One at a time.

"Is it really up to the "person" to decide?" In my opinion, for this hobby, the answer is yes.

How people process sound, especially when it comes to music which is intended to strike emotional portions of the thought process, is very much individual. There's been lots of studies showing that it is part genetic and partly it is learned. I don't even pretend to imagine to be highly knowledgable in this area, so I'll accept the word of the people who devote their careers to studying this.

If this was not true, then why do all the perceptual testing for codecs like mp3? The testing was performed to find a common ground of what was acceptable for the application. Emphasis on the word acceptable. If everybody was alike, or at least statistically so, why not just use the results from a single person's testing?

"something is audible while controlling for the inevitable psychological biases than blind testing?"

Except for one thing. I have all sorts of psychological biases when I sit down to listen to music. Yup, I said it. Sorry, opera and rap music do not do it for me. Nothing against fans of each genre, but it's not what I'm interested in listening to. I am equally sure that I am flawed in what aspects of a music reproduction spark my interest. My wife has different priorities in what parts of the music reproduction are desirable or unacceptable for her. Thankfully, we are pretty much able to find something that works for the two of us.

Listening to music is a hobby. So, finding the ultimate "truth" is not really that important, if it is even possible. Especially so when so much of the original performance, if it even was truly performed by humans in the same room at the same time, has been doctored along the way to produce something that met somebody's idea of "right" or commercially desirable. As a simple example, go listen to however many versions of Tommy by The Who that you can download or purchase on CD. Then go listen to the short excerpt from that album that Mikey Fremer posted on YouTube in a video about record wear. Which one is The Truth? Did Pete Townshend not know what he wanted to convey the first time around? The record companies are in the business of selling product, as the saying goes. Anything else is a means to that end.

"you could always complain that the measurements used are "limited"!"

Huh? So, some statistical test performed under conditions that are not like how you actually listen to music are ok, but my wanting better engineering testing and examination is a bad idea? Wait - I guess accepting incomplete testing from a psychological standpoint is consistent with accepting incomplete engineering testing. My bad!

My own view is that the blind test thing always comes out when somebody wants to show that somebody else's listening observation is at odds with their own personal dogma. Not always, but you can count on it just like you can count on Hitler eventually coming up in a political discussion. (Godwin's law)

Do audiophiles jump to erroneous conclusions? Yes! Proof of that is how they'll buy something new soon enough.

Do manufacturers throw out bogus explanations in their promotional materials? Yes! Unfortunately, it seems to work for them.

It all may be annoying, but very much a first world problem. (My own very personal complaint is that very earnest people are looking for information on products that might allow them to listen to music in a more enjoyable way for them. They might find a review like the one above, which offers one man's opinion of how the product worked for him. But, they also will find faux-scientific explanations as well as people telling them that what they might experience with their own ears is clearly wrong and not what they like. Just great...)

https://www.youtube.com/watch?v=cHxGUe1cjzM

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 1:55pm

Yet, people still "shop" and plunk their money on whatever they want...

And the audio industry continues to thrive.

The best use of DBT or even SBT (easier, less costly to apply)?

To weed out the "junk" that inevitably ends up in the landfill and pollutes the environment.

michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 2:41pm

What's next? The right to vote?

;-)

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 2:52pm

Yeesh!!

ACranston's picture
Submitted by ACranston on June 27, 2019 - 12:35am

Your words are so wise, Archimango! 99.9999% of audiophiles are truly audiofools. I have been blind since birth and so all the testing that I do is truly blind testing. Often, I will test twice because double blind testing is the best way to do it and what I will categorically say is that all speakers, amplifiers, music servers, and cables sound exactly the same. After all, it's just a bunch of 1s and 0s and so no one needs more than my Bose setup.

P.S. Let's find another article where people claim they hear things that they really don't so we can show them the errors of their ways!

Long-time listener's picture
Submitted by Long-time listener on May 17, 2019 - 8:13pm

"I agree, the dichotomy should not be there...IMO, it's because the "pure subjectivists" don't believe in blind tests. So don't bother taking them and continues to make claims of massive differences!"

If I'm not mistaken, I believe John Atkinson himself (up until recently, Stereophile's editor, if you'll recall) recently weighted in on this subject, feeling that strictly controlled tests simply can't reflect the way we usually listen to and experience music. And I think very few people make claims of "massive" differences. Lab measurements provide most of what we need to know regarding objective measures of performance.

Archimago's picture
Submitted by Archimago on May 19, 2019 - 10:02am

Agree.

Although I wish JA would stop painting blind testing in a negative light with his experience of amplifiers from the 1970's :-). I have faith that in time he will.

Ortofan's picture
Submitted by Ortofan on May 19, 2019 - 11:27am

... of removing extraneous factors, such as level mismatches, knowing what the equipment costs, looks like and its brand name, so that the listener can concentrate purely on trying to perceive whatever differences in sound quality may, or may not, exist?

michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 11:54am

....what the things they buy look like.

Are you suggesting this is....wrong/bad/misguided/silly?

I’d be careful how you answer that :-)

Ortofan's picture
Submitted by Ortofan on May 19, 2019 - 2:20pm

... only one variable at a time should be considered.
If aesthetics are your top priority, then use that factor to cull visually unappealing products from your shopping list.
Then move on to an unsighted comparison of sound quality.

michaelavorgna's picture
Submitted by michaelavorgna on May 19, 2019 - 2:29pm

...to dictate the terms with which other people should go about buying a hifi?

Please explain why that's the case and how's that's working out for you so far.

Ortofan's picture
Submitted by Ortofan on May 19, 2019 - 3:11pm

... using a controlled experiment to test a given hypothesis - such as does one piece of audio equipment sound any different, let alone better or worse, than another.

You still spend quite a bit of time posting comments on the site of the organization that made you a redundancy.
Wouldn't your efforts be better directed toward creating new content for your own site?

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 4:03pm

How do you define "scientifically"...

...better or worse?

How about just "different"?

michaelavorgna's picture
Submitted by michaelavorgna on May 20, 2019 - 2:50am

I'll take that as the best answer you have to my question.

Regarding time etc., while I appreciate your concern, there's no need to worry - I take a measured approach.

Cheers.

ken mac's picture
Submitted by ken mac on May 25, 2019 - 12:10pm

...when Michael states an opinion, which is different than your own. When you run out of reasoning, you move on to insults. Please, just move on.

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 2:14pm

...not exist for another listener with different source material in a different environment and sound system.

John Atkinson's picture
Submitted by John Atkinson on May 19, 2019 - 3:05pm
Archimago wrote:
I wish JA would stop painting blind testing in a negative light with his experience of amplifiers from the 1970's :-). I have faith that in time he will.

I have taken part in more than 100 blind tests since my first in 1977, as organizer, proctor, or subject. My opinions on their efficacy or lack thereof are based on that experience. See www.stereophile.com/content/simple-everything-appears-simple.

John Atkinson
Technical Editor, Stereophile

Ortofan's picture
Submitted by Ortofan on May 19, 2019 - 3:16pm

... structure a "blind" - or single variable - test of comparative sound quality in such a way as to eliminate your objections to that testing method?

ChrisS's picture
Submitted by ChrisS on May 19, 2019 - 3:58pm

...inappropriate for audio reviewing.

It is time consuming and costly to apply DBT properly. Look into research methodology and testing- it's not something you can apply in your basement or living room! Of course, you can do single blind testing in a "casual, informal" way for the kind of results that you are looking for... You might actually get informative results, but those results may not have any bearing whatsoever outside of that specific test situation.

As mentioned before, different listener, different source material, different listening environment, different sound system, etc. invalidates all previous test results.

See JA's article above.

ChrisS's picture
Submitted by ChrisS on May 20, 2019 - 1:58am

Have any of you, those who keep asking Stereophile to do DBT's, ever participate in or perhaps know how to design a proper DBT or SBT?

Sounds like Ortofan remembers something about the "scientific method" from grade school, but does anyone else have any experience with research methodology or test design from college or university?

Anyone?

Timbo in Oz's picture
Submitted by Timbo in Oz on May 23, 2019 - 9:41pm

Bind or sighted.

It is common to see a value for Beta of over 0.5, while the value of Alpha is kept well below that.

This speaks more to the commitment of some folks, than any real understanding of what 'proof' is.

Given that, my test is, what's the value of Beta?

allhifi's picture
Submitted by allhifi on June 21, 2020 - 4:59am

Finally ! There is one (CG) who presents the issues from fresh eyes. As CG so appropriately pointed out in his reply, NO ONE seems to question, or investigate such phenomena ? Laziness. Plain. And simple.

What has been "said" in this industry decades ago (Hearing Memory is weak/short, 'Expectation Bias' and so forth) has been taken at face value without seeming interest in evaluating further -or even validating rigorously. Those 'statements' and many other accumulated/used over decades keep getting re-hashed and used/thrown about by everyone for reasons unclear to me; perhaps to demonstrate (to readers) they are on the cutting/leading edge of the arguments -that have been floating around for decades?)

There is a tiny group of people -perhaps a handful- that DO understand the complexities involved, the current disparity in understanding the relationships (electric, acoustic, temp/humidity -magnetic atmospheric radiation -the list goes on-and-on) and slowly, methodically investigate such factors in hopes to add data/understanding to the current 'mysteries' of sound reproduction.

CG stated it accurately (and wisely) in stating:

" ...My own experience ..... is that a lot of these little things that seemingly make no sense from a scientific perspective really do make sense once you dig deeply enough. There are lots of engineering design "rules" that are accepted as being perfectly fine but really are only ok, at best. When you examine very closely, you can not only find flaws through analysis but through actual measurement. The problem seems to be that nobody wants to go to that length, unless a problem pops up. (Think of the O-rings on the Space Shuttle.)"

Ohh, so (sadly) true.

It's high-time (literally these days) to start a fresh, new thorough investigation; dispensing with old myths/half-truths and really engaging in some genuine ground-breaking investigations in effort to to generate greater understanding to the apparent mysteries that surround sound quality/reproduction perceptions.

peter jasz

CG's picture
Submitted by CG on May 17, 2019 - 1:22pm

About volume controls...

Ever measure or simulate what happens as you adjust the level of a volume control on most preamps? In many of the designs (half? more?), the overall bandwidth is lowest at the -6 dB setting of the volume control. That's because the output impedance of most volume controls is maximum at that spot. In concert with the input stage capacitance, the RC low pass characteristic gives lowest bandwidth at that point. Of course, there's ways to minimize that effect.

In addition, many input stages become less stable at various volume control settings and various source impedances, including the parasitic capacitance and inductance associating with the connecting cable. (The explanation for that one involves real math and is way too lengthy for discussing here. There's articles from professional journals that can be accessed on line. Or, just go measure or simulate the circuitry, if you want proof.)

Point is, as I mentioned above, there is often a good explanation for behaviors you might observe by listening carefully, but are not normally considered in design or testing. That is, unless you specifically look for it. (It's very easy to *say* that everything should be looked for...)

One other thing thing: Full, complete disclosure - I have never seen, never mind heard, any piece of Pass Labs equipment. I might recognize Nelson Pass at an audio meeting of some kind, but only because I've seen pictures of him. I wouldn't know Wayne Coburn at all.

MarkusL's picture
Submitted by MarkusL on May 17, 2019 - 2:07pm

Using a Wadia 781i which should sound fine without a preamplifier, I found that the sound is much better with a preamplifier (Audio Research Reference 5 SE) between the Wadia and my pair of Pass X 600 power amplifiers!

monetschemist's picture
Submitted by monetschemist on May 17, 2019 - 6:36pm

Is it just me? Or does an extremely well-designed, well-implemented machine like pretty much anything Nelson Pass has ever built actually have some intrinsic value, both in terms of quality of audio experience and just that je-ne-sais-quoi that comes from a fantastic piece of gear? And that Pass Labs makes something like this available at less than the price of a used Honda Civic whereas "certain other purveyors of audiophile exotica" add another zero to the price?

Long-time listener's picture
Submitted by Long-time listener on May 17, 2019 - 8:17pm

"It's true that aural memory is poor..."

Is that why I once was able to recognize, within three seconds, the voice of an old friend I hadn't heard from in 10 years, over a poor quality long-distance connection, without knowing in advance he was calling?

As long as we have adequate time to become accustomed to, and to recognize and characterize the qualities of a particular source, we can actually make pretty good comparisons with other sources based on memory.

jimtavegia's picture
Submitted by jimtavegia on May 19, 2019 - 7:32am

I would never trust my audio memory for more than a few minutes. If I really had an audio memory I would not have had to take lecture notes. Trying to write down in words what my musical listening experiences at a any given moment are with certain gear could be meaningless hours or days later. Compare a glass of wine from today to one from a month a go? Hardly.

We do know differences from the immediate changing of gear, cables, carts, etc. , which makes sense to me as I have done it time and time again. To me, it must be in the near same moment or all bets are off for my memory.

Long-time listener's picture
Submitted by Long-time listener on May 19, 2019 - 11:06pm

Yes, many people feel that aural memory is too short-lived to be useful. But I think that's based on a misunderstanding of how memory works. I may not be able to make "precise" comparisons of glasses of wine (to the extent that such subjective appraisals are "precise"), but I can remember whether what I drank a month ago was good, and whether what I'm having now is better or worse, and in many respects, I can also judge how it differs--assuming I'm someone enough into wine to do that in the first place. Same with audio. As an example, I have a particular CD ("Sweet Jones" by 9Lazy9), and on track 4 there are cymbal taps following the introduction. Since that CD is very familiar, and I have listened to it many, many times, I have a very clear impression of just how prominent and clear those taps were on my earlier speakers (Dynaudio Excite X12 and Special 40) relative to the ones I listen to now (Buchardt Audio S300 MKII). As long as there IS a clear difference--and in this case there is--and we've had time to home in on what it is, I believe memory is pretty trustable. That's what I'm saying when I talk about having enough to time truly become familiar with something. No one remembers every word of a lecture, just as no one remembers every note of the music they've just heard. That's not the issue, and not what is meant by aural memory (unless you're claiming that we must have perfect eidetic memory before our memory can even be considered competent). But if you become familiar with the voice of your lecturer over say a semester, then you would recognize, even with your eyes closed, if a different lecturer had taken his or her place. (The issue is the "sound" of his or her voice, not what was said.)

Long-time listener's picture
Submitted by Long-time listener on May 17, 2019 - 8:22pm

When I replaced my Kimber KS2020 coaxial digital cable with a new Audioquest Diamond cable, I did not hope or expect that there would be break-in. I hoped it would sound good straight out of the box. So I was dismayed to find there was unpleasant brightness and glare and I assumed I had bought an inferior cable. But since I knew about break-in effects I gave it some time, and within a few hours the treble became less forward and the bass solidified. It's now a beautiful sounding cable, providing better clarity than the old Kimber.

DH's picture
Submitted by DH on May 17, 2019 - 10:38pm

Euphonic distortion
Better match to your amp than the output of your DAC
Doesn't matter as long as you like it.

Bogolu Haranath's picture
Submitted by Bogolu Haranath on May 18, 2019 - 6:24am

May be Mr.Austin would be interested in reviewing the McIntosh C52 pre-amp ($7,000)? ........ C52 has built-in DAC and headphone output ........ C52 also has a bypass-able 8 band parametric EQ .......

There are several very favorable reviews posted online for C52 :-) ...........

Bogolu Haranath's picture
Submitted by Bogolu Haranath on May 18, 2019 - 7:20am

Absence of (scientific) evidence is not evidence of absence :-) .........

ok's picture
Submitted by ok on May 19, 2019 - 10:00pm

..a live orchestra inside your house playing only “as the artist intended”? I know I wouldn’t!

tonykaz's picture
Submitted by tonykaz on May 21, 2019 - 5:59am

dam good point.

Who the hell wants a Live Band or a dam Orchestra blaring away when we've had a rough week and/or need some Peace ?

You point out something I've had trouble putting my finger on.

Thank You,

Tony in transit.

tonykaz's picture
Submitted by tonykaz on May 21, 2019 - 6:30am

China has been the World's largest Manufacturer for the last 2,000 Years ! , they've had a few weak decades from time to time but they've always been "THE" Super Power in Manufacturing.

Our beautiful little Audiophile Industry needs ( and deserves ) our priority! People like Paul McGowan, Schiit, KEF's Ray Cooke, Ivor at Linn created the foundations of our hobby. I'm stay'n Loyal !!! I'm here to support "OUR" Guys that don't go to Asia to get "OUR" stuff made, because "OUR" Shop labor is made up of "OUR" children and "OUR" next door neighbors.

Manufacturing wise, the USA is tiny, 25% of China's Size but has easily made twice as much annually .

China is now, once again returning to Dominance via their Centuries Old Socialist Republic System. Nobody is gonna slow them down, they don't do Wars ( only one in the last 500 years, Viet Nam, China lost ), China is now replacing our Petrodollar with the PetroYuan .

China's weakness is their Money. Does anyone trust China's Money?

I'm writing this in recognition & admiration of China's Greatness and as one of it's Competitors .

Tony in transit

ok's picture
Submitted by ok on May 22, 2019 - 2:59pm

https://www.youtube.com/watch?v=hcYSl2fTAic

BB's picture
Submitted by BB on May 21, 2019 - 2:12pm

Pass Lab’s best preamp may be their headphone amplifier, the HPA-1, when used in its preamp mode. It is single-ended only. Plus you get a world-class headphone amp in the deal. Stereophile should do a comparison even if it doesn’t please an advertiser.

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