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In Reply to: RE: August Stereophile Amplifier Measurements - an observation, or two. posted by 13th Duke of Wymbourne on July 14, 2014 at 14:53:47
>In summary, there is nothing special about the Lamm's intermodulation
>result. It follows what should be expected from the harmonic distortion
>results.
Thanks for reading my measurements sections so carefully. A lot of work
goes into these.
The comment on the good intermodulation performance of the Lamm preamp
that I made concerned the fact that the IM test I used has tones at 19
and 20kHz. Some tubed designs have increasing harmonic distortion at
these frequencies, perhaps due to the circuit's limited open-loop
gain-bandwidth product. That the Lamm preamp has exactly the HF IM
behavior that you would expect from the lower-frequency harmonic
distortion results reveals that it maintains the linearity of its
transfer function at the top of the audioband, which is indeed excellent.
Regarding the Dan D'Agostino preamp, I was indeed puzzled by the
difference between the channels' transfer functions. The appearance of
even-order distortion in one channel indicates a gain mismatch between
the hot and cold sections of the circuit, perhaps due to a component
value error.
John Atkinson
Editor, Stereophile
Follow Ups:
I find that you do a great job in these times of willy-nilly commenting that passes for reviews in providing one of the few efforts in actually providing some objective measure of performance. Not a mean task nowadays!
> I find that you do a great job in these times of willy-nilly commenting
> that passes for reviews in providing one of the few efforts in actually
> providing some objective measure of performance.
Thank you. I have written a guest editorial for the next issue of Jan
Didden's "Linear Audio" journal on why audio component reviews need
to include measurements to be considered complete.
John Atkinson
Editor, Stereophile
Serious question:
Would cable measurements ever be a possibility?
> Would cable measurements ever be a possibility?
I have long wanted to publish LCR values for cables but this has remained
on my "important but not urgent" list forever. But the real problem with
cables is what actually to measure? I suspect that when you change a cable
in a system, you are changing the character and level of the system's noise
floor. So any measurement would be system specific, including such aspects
as the RF environment in the listening room.
John Atkinson
Editor, Stereophile
Thanks for your response. The question besides WHAT to measure, is what CAN you measure..L,C,R..but also bandwidth? EMI/RFI rejection? Conductivity?
I think it would be most interesting to correlate to listening. And cable manufacturer claims.
With an adquate tape measure you can ascertain lenght...
I would like to know what "beyond reproach" means given all of the discussion on this thread.
> would like to know what "beyond reproach" means given all of the
> discussion on this thread.
The "beyond reproach" comment applies to the left channel, as I tend to
give manufacturers the benefit of the doubt in cases like this. It is most
probable that the problem with one channel is specific to that sample.
But perhaps I was too forgiving in this case. :-(
But even so, the only reason people knew that there was a (small) problem
with the Momentum preamp's right channel was because I told them in the
review.
John Atkinson
Editor, Stereophile
I think you were a bit too forgiving, John!
No need to slam the d'Agostino but I was left scratching my head upon reading the measurements of the Momentum and then your conclusion that it was great engineering. You should have concluded by "this weird behaviour in one channel deserves an explanation from the manufacturer".
Because it's certainly not "heroic audio engineering"! Hopefully it's just a faulty component or a mistake but at the price, it shouldn't happen.
JB
Edits: 07/20/14
Good one. ;)
Never trust an Atom, they Make Up everything!
John, would you be willing to share with us what you to prepare your measuring instruments for a measuring session?
Who are the mfg'ers and what models do you use and what is their age?
Are your measuring instruments recalibrated from time to time?
Also, do you do any special prep for the component or speaker about to be measured?
Thanks,
> John, would you be willing to share with us what you to prepare your
> measuring instruments for a measuring session?
A couple of hours' warm-up of both test systems and DUTs, to ensure that
all are stable. With electronics, experiments with grounding between DUT
and test system to get the noise floor as low as possible.> Who are the mfg'ers and what models do you use...
I mention these in every review. Measurements of amplifiers and digital
products are currently performed with my top-of-the-line Audio Precision
SYS2722 system. For some tests, and to check the results of others with a
different measurement system, I use my vintage Audio Precision System One
DSP and a 1999-vintage PrismSound DScope 2 with an Ayre QA-9 A/D
converter. Other products include a Fluke 87 digital multimeter, Kenwood
and Hitachi analog oscilloscopes, an 8-bit Heath digital oscilloscope,
Heath oscilloscope calibrator, and a Neutrik Minirator signal generator.
For loudspeakers, I use DRA Labs MLSSA system and SMUGSoftware's
FuzzMeasure 3.0 programs, with calibrated DPA 4006, Earthworks QTC-40,
and Mitey Mike II microphones, Earthworks and Metric Halo microphone
preamplifiers, and an Outline speaker turntable.> And what is their age?
The AP System One dates from the early 1990s, the SYS2722 from 2007, the
MLSSA system from the late 1990s. The microphones range in age from 1989
to 2006.> Are your measuring instruments recalibrated from time to time?
The System One is no longer supported by AP; the SYS2722 was last
calibrated 3 years ago and is due for recalibration. At the start of
every speaker measuring session, I measure the tweeter-axis response of
a 1978 LS3/5a and compare that with the earlier responses of the same
speaker. On a less regular basis, I compare the response taken with each
of my 3 measurement microphones with those taken with the others and to
check MLSSA, I repeat the response measurement with different hardware:
Fuzzmeasure on my laptop and a Metric Halo Firewire A/D.
John Atkinson
Editor, Stereophile
Edits: 07/18/14
Thanks for the info, John. Good stuff.
On another note, I remember you stating in I think the Sept, 2009 issue when a group of you were doing some comparisons between live piano and that same piano played back via a recording of that live session, that even though you heard some good qualities in the playback, it was your opinion that much of the live music being recorded never made it to the recording medium. (I'm paraphrasing of course.)
But I don't recall your elaborating on that point.
Anyway, is that still your take today?
Thanks,
> Thanks for the info, John. Good stuff.
You're welcome.
> I remember you stating in I think the Sept, 2009 issue when a group of you
> were doing some comparisons between live piano and that same piano played
> back via a recording of that live session, that even though you heard some
> good qualities in the playback, it was your opinion that much of the live
> music being recorded never made it to the recording medium. (I'm
> paraphrasing of course.)
> But I don't recall your elaborating on that point.
I summed up my opinion at the article page linked below.
John Atkinson
Editor, Stereophile
Thanks, John. You call that a summation? :)
Nice writing style, John, and very provocative too. You’re obviously quite deep, thorough, and well-informed. I admit that I have yet to finish reading the entire dissertation.
You bring up some very good points throughout. Too many to list actually for my limited short-term memory to recall. You dive into levels few consider, including the internal modeling, etc.
Nevertheless, there are a few points that stood out in your writings. But have you considered the possibility that:
1. Just because you dive deeper than the average bear and because you’re a thinker and a sound engineer and an editor-in-chief of a popular magazine should never automatically imply that you’re postulates are correct. Nor should one automatically assume they are wrong either. For example, you postulate that inner modelings have occurred in the listener whereas this cannot be proven right or wrong. Or that you yourself have your own inner modeling occurring that may lead you to incorrect assumptions.
2. Like any subject, one can go as deep as they want and loose many along the way. Especially when so many struggle with just the fundamentals back at the surface.
3. That in your quest to dive deep, you yourself are in uncharted territory, and in the end could be as far or maybe even further off the mark than those who remain at the surface? For example, when a gent like yourself pulls back the covers on a given topic, you are in uncharted territory and you open up a slew of new variable to consider, including those that you mention as well as those you may have overlooked including some-to-many traced all the way back to the surface.
For example, if we go back to my first question to you about your sensitive measuring instruments. You mentioned how some of your equipment was antiquated, out of production, no longer calibrated, etc. Those are potential shortcomings to others and should raise questions for those who put stock into your published measurements. Additionally, what are your thoughts about sensitive measuring instruments unable to discern differences that a well-trained ear can?
But more importantly, in your response about your sensitive measuring instruments, you neglected to mention taking any precautions whatsoever regarding the possibility of minimizing the affects of noisy AC or under controlled vibrations having potentially any effect on your resulting measurements. Nor do you make mention of what platform you use to place the component under review on nor do you mention the platform upon which your sensitive measuring instruments are placed. For example, are you using a kitchen table, an antique coffee table, a sophisticated bench, etc, and do you use the same platforms for every test made?
Another point worth mentioning is that to the best of my knowledge you’ve yet to mention the potentially inferior hearing abilities of at least a few of your esteemed colleagues. Surely, like some of us, you’ve encountered such types who quite frankly couldn't punch their way out of a music bag if their lives depended on it. Such types would potentially and significantly skew the results of any listening tests of any type.
Also, regardless of the playback system, what if in all of your endeavors you are only be hearing a small percentage of all the music information that is embedded in a recording, all of which may be processed, yet the vast majority remains inaudible due to a very high noise floor inherent in every playback system.
For example, as mentioned earlier, you stated in the Sept. 2009 issue regarding the live piano vs recorded that you speculated much of the live music never reached the recording. Moreover, Robert Harley of TAS stated in the Mar/Apr 2009 issue that he speculated that something catastrophic was occurring at the recording mic’s diaphragms so that much of the music never made it to the recording. Harley reported elsewhere that he arrived at this conclusion based on a rather simple test performed by Ed Meitner, hence we can probably assume Meitner also arrived at a similar conclusion. Then there's Jonathan Valin of TAS stated in circa 2007, “We are lucky if even our very best playback systems are able to capture even 15% of the magic of the live performance.” To Valin’s point I know a few who said even that 15% is being optimistic.
Hence, I ask, in all of your research, listening tests, and studies and postulations about hearing and listening and interpreting, what if you discovered that what we hear from a given playback system has been based on your (and everybody else) hearing perhaps only 1/3rd of all the music info embedded in a given recording, regardless of format?
Since to some exent you seem to have already admitted to this serious deficiency, as have some of your colleagues, how does that factor into your postulations?
I'd be interested to hear your thoughts.
Thanks,
On the MOMENTUM preamp...That looks like a "gear" operating the volume control/meter contraption,,,,
Hello John,
Just thought you should know that 'hot and cold' is a concept that does not apply to a balanced circuit of any kind- such associations lead to confusion.
There is 'inverted' and 'non-inverted'. Neither is 'hot' and neither is 'cold'- each signal has the same value. Balanced connections are not compatible with single-ended connections; the use of 'hot' and 'cold' often leads to the idea that there is compatibility (and a lot of hum/buzz problems as a result).
The reason balanced connections are not compatible is that a balanced system ignores ground. Many years ago you measured one of our preamps and found a large amount of diode noise; this was because the tester you used (Audio Precision) at the time made all its measurements from ground- and hence was not able to really test a real balanced-line product. Imagine an output transformer with no center tap and no connection to ground driving an output: pins 2 and 3 of the XLR, with ground being the circuit ground and nothing more. You have an incomplete connection if you measure from ground to either pin. IOW the output occurs between pins 2 and 3 and nowhere else. This is how a true balanced line connection works.
So I thought I might take this opportunity to point this out as after all these years there still appears to be many misconceptions in the high end audio community regarding balanced line operation- this one being one of the more common ones.
All the Best,
Ralph
'cause it's the truth!
John,
thanks for the reply and keep up the good work.
Did the left channel of the Momentum have a 1kHz difference tone? I can't tell if there's a blue peak hidden behind the red one in Fig.8. Hopefully not, then theory would be correct and it's nice when that happens.
Regards
13DoW
> thanks for the reply and keep up the good work.
Thank you.
> Did the left channel of the Momentum have a 1kHz difference tone? I can't
> tell if there's a blue peak hidden behind the red one in Fig.8.
Apologies for the late response on the Asylum. To repeat what I said via
private email, no the left channel didn't have the difference tone at 1kHz
in its HF intermodulation spectrum. And as you pointed out, the second-
harmonic distortion in the right channel might not be due to a slight
difference in the "hot" and "cold" signal paths, as I conjectured, but to
a small DC offset in an intermediate section, which will also give rise
to waveform asymmetry.
John Atkinson
Editor, Stereophile
"Two silly-expensive preamplifiers, from Dan D'Agostino Master Audio Systems and Lamm Industries, are featured in the August Stereophile and both offer sound quality and measured performance that are beyond reproach. " [emphasis added]
http://www.stereophile.com/content/august-issue-here
I guess being "puzzled by the difference between the channels' transfer functions" is still within the boundary of beyond reproach.
Hmmmm ....?
Well that certainly doesn't seem to be the case for the OP, an obviously informed commenter ... "I think it shocking that a $42k preamplifier should have 30x the second harmonic distortion in one channel compared to the other".
Never trust an Atom, they Make Up everything!
"Regarding the Dan D'Agostino preamp, I was indeed puzzled by the
difference between the channels' transfer functions. The appearance of
even-order distortion in one channel indicates a gain mismatch between
the hot and cold sections of the circuit, perhaps due to a component
value error."
No doubt then you dutifully stated it could not be recommended due to poor engineering.
Never trust an Atom, they Make Up everything!
Living in Hong Kong - this is arguably the "watch" capital of the world where you can easily drop $3,000,000US on a watch.
As was pointed out to me though - most of these companies are not at all in the business of selling watches (indeed many don't actually tell good time)- they are in the business of selling "prestige."
Some companies will sell both prestige and quality.
I know you and I don't agree on SQ so much given that I prefer SET/HE but I do like SS systems but I take a much more utilitarian approach to the latter systems.
If I am going to spend big money on say a $100K solid state system with big monoblock power amps then I want serious performance. The point of SS based systems is to get the best conceivable measured response.
Tube SET guys - we care about sound quality even if what we like is various distortion - make no mistake we choose these systems on subjective touchy feely preferences not because of the measured performance.
But the SS buyer is looking for technical superiority and power and superb measured performance (in every and all aspects). And that's why I don't really get products like the Momentum. It doesn't sound as good as a good SET amplifier at prices that have one less zero in the end. And so subjectively it's tough to get behind them.
Then for the utilitarian measurements guys it falls flat on its face for the dollars. It's mediocre for SS technical superiority.
Heat sinks should sink heat properly. I mean this should be the first and foremost consideration for any serious power amplifier. The amp will run maximum level into 0.001 ohm 24/7 for 20 straight years.
At that price the transformers should be designed and built in house, so should most of the internal parts. You should not be phoning up a glorified parts express to buy a torroid. The copper chassis is nice and all - icing on the cake but that seems to be the major selling feature. My Pioneer Elite receiver in the mid 1990s for $2k had a copper chassis. It's not exactly expensive. Is the internal wiring at least silver? Doubtful.
I'd like to see the High Quality parts - not seeing it. Nothing there that looks better than amps well under $10k.
The first thing you do with a boutique piece of jewelry like this is directly compare it to what serious amplifier designers are putting out - something from say Nelson Pass or for that matter Ralph above.
And while some may say "it's about the sound" - maybe but the eyes are well known to deceive the ears.
I am not seeing the quality.
You know the sad thing (and funny thing to me anyway) is that this is coming from a fan of Audio Note equipment that is often considered to have loopy pricing. I don't have a problem with pricing if there are parts that in some way justify it.
But compare the Momentum preamp previously above at $32,000 and the Audio Note M6 preamp for $18k (the M3 is $10k which is exactly the same amplifier but uses lesser parts (EI transformers instead of nickel C-core etc).
The M6 is still a heckuva lot of money no question but considering that they make the transformers in house, the wiring is all silver (which they make in house) to their own caps, resisters, cables, the actual connectors, volume pots. And when they do use an outsourced part it is usually at or near the best available for whatever it is.
So while I can say the M6 is expensive I can actually see where the money is. I struggle to see it in Solid State makers. Virtually all of them buy off the shelf parts and put their label over the front. At $5k ok - at $50k not ok.
I agree with the basic gist of your two posts. I always scratch my head when I look at the insides of almost all SS components, I usually see lots of 25 cent resistors, $2-5 dollar capacitors, circuit boards and wiring that appears to have been taken out of a $250 desktop PC. It just does not add up.
Welllllll theres not too many carrage trade parts manufactures..
...for these budget components?
;-)
.
Never trust an Atom, they Make Up everything!
SSOOOOOOO,,,, HOW DID THEY SOUND ???????
The judgements that Atkinson makes on components based upon measurements are largely separate from the question of sound quality. This is abundantly obvious since on many occasions he has disqualified a component from receiving a Stereophile recommendation despite an enthusiastic subjective evaluation by the reviewer.
Never trust an Atom, they Make Up everything!
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