John Curl's Blowtorch preamplifier

[john curl]

It is deeper than that, Chris, although it is universal, I agree.

[chascode]

Originally posted by john curl
Chris, check out the Mar 'Stereophile' with the JC-2 preamp review.

Originally posted by john curl
I like graphs and measurements that even I can't do easily, if at all. ;-)

John, great job on the JC-2, and the cost is really quite reasonable. I agree with you on John Atkinson's measurements for Stereophile, and the new AP has even better resolution. His stated goal is to try to correlate the objective with the subjective - a major task that may or may not be possible even with state-of-the-art test equipment. All the other audio magazines treat technical guys like children...."there, there. You really don't have any need to see all that confusing and complicated data. Here, we have some new adjectives for you to play with"

Best Regards, Chuck Hansen

[GRollins]

Until someone does find a way to correlate measurements with the sound quality, what purpose does it serve to repeat numbers that are meaningless (and can readily be found on the manufacturer's website)? To impress people? Who? The only people impressed by the standard numbers are people who haven't listened to two amps which on paper have identical specs, yet sound notably different. People who have listened are justifiably skeptical of THD, damping factor, etc. There's no reason to trot out the numbers except to give a thin veneer of respectability to the review.
The only exception as I see it would be a component that did not meet specifications. That, in turn, raises the question of whether the piece was damaged in shipment or was perhaps defective...or did the manufacturer claim more than they could deliver? In this case, I believe that it would be interesting, not so much from the direct implications of the numbers for sound quality, but for what you might deduce about the manufacturer's honesty.
All of this could change in a heartbeat if someone comes up with a new spec that actually means something, but I'm not holding my breath. Progress is slow to say the least. In the meantime, save the ink, save the paper.
To the extent that someone claims to be trying to find a correlation, my hat's off to them. But are they really? Where's the article detailing their research, whether the results are positive or negative? I, for one, would be interested to read an article like: Well, we thought we'd see if damping factor actually correlated to perceived tightness of bass and here's what we found. But oddly, I never see articles like that. On the rare occasion someone does attempt something of the sort, they only compare two or three amps, which is hardly going to give you a statistically worthwhile answer; how do you know the bass wasn't better due to a bigger power supply, for instance--something unrelated to damping factor. In short, I think a strong case could be made that (other than catching a few components that don't meet spec) the reviews in question are simply printing the charts and numbers to make their reviews more 'scientific' in some peoples' eyes. If I want the specs, I can always look at the literature for the piece.
I hope someone, somewhere comes up with something clever. It would be nice to have a reliable test that actually told us something about sound quality.

Grey

[john curl]

Numbers do matter, and I am glad that 'Stereophile' still measures them. However, you have to interpret the numbers properly to get anything that is really useful. Most people can't do that, and it is not in any book.

[PMA]

Originally posted by GRollins
Until someone does find a way to correlate measurements with the sound quality, what purpose does it serve to repeat numbers that are meaningless (and can readily be found on the manufacturer's website)? To impress people? Who? The only people impressed by the standard numbers are people who haven't listened to two amps which on paper have identical specs, yet sound notably different. People who have listened are justifiably skeptical of THD, damping factor, etc. There's no reason to trot out the numbers except to give a thin veneer of respectability to the review.

As many times, you do not know what you speak about. There are no 2 different audio components with same set of measured graphs and spectra. The only problem is that you have to understand those measurements, and to add some not shown. Do not disapprove something you apparently do not understand.

[AKSA]

I would say, Pavel, that Grey is entitled to any opinion he wants.

Furthermore, your implied arrogance here is vaulting, and even you, for all your self-professed knowledge, cannot fully correlate measurement with statistically based listener preference. In truth, no one can, not even Earl Geddes - who comes closest in my view.

This obsessive concern for the measurements might one day reveal something very worthwhile, but not yet, and your opinion is not worth more than others here, in part because of your sneering attitude to others. Until this correlation is well understood from every angle - PSpice analysis, distortion spectra, operating points, topology - then good design will remain something of an art and certainly will require multiple iterations to get right.

Hugh

[h_a]

A very impressive preamplifier!

Mr Curl, I saw the JC-2 pre uses an R-core transformer. Since it appears to me these are seldom used and there's little hands-on experience with these, I would like to ask you what your experiences with these type of transformers are (though I know that it was probably not your decision to use them).

Thank you very much, Hannes

[KSTR]

Originally posted by AKSA
In truth, no one can [fully correlate measurement with statistically based listener preference], not even Earl Geddes - who comes closest in my view.

According to this paper, Moore et al even come closer.

The real "problem" is that virtually nobody in the industry (both the audio test gear and audio reproduction branches thereof) has adopted these new and way better sound quality metrics (and quite complicated to derive), at least to my knowledge. A single number THD value and even the full spectrum (mag/phase) it was derived from is close to meaningless if one doesn't know how to correlate that to the perceived sound quality. That's where Geddes/Lee, Moore etc spent their efforts in: a more useful and more realistic interpretation of the given data. There is still a lot of work ahead, say correlation of measurements of stereo channels to perceived "imaging", for example... it will be done, sooner or later.

- Klaus

[PMA]

Very good link, Klaus.

[john curl]

It does take more than one measurement to give a meaningful evaluation. However, it is possible to derive a lot of subjective information from the measurements in a 'Stereophile' review, especially if the better test equipment is used. Unfortunately, the older set-up had residuals that implied higher order distortion on many products, at a level that was inaccurate.