Well, we're even, you did the same for mine. Unless, of course, you were serious and think that a low static THD at one frequency into a test load is a sufficient criterion. Load tolerance, stability, source impedance, IM, bandwidth, noise, overload recovery, clipping characteristics, none of that (or anything else) seems to be taken into account.
BTW, that Ayre spectrum is very unimpressive. I thought that their stuff had much lower distortion than that. It makes my tube amp look like a specs king.
AKSA said:
Hugh,
I did understand your point from the start, as you elaborate further in the post quoted above.
My point is, once you finish what you call the first stage, the engineering process leading to certain performance parameters, any further modification must involve deviations form the just attained baseline.
Otherwise, being objectively measured improvements then they qualify within the first design stage.
Be it that way, then any further tweaking to meet subjective listening goals implies loss of accuracy. There is nothing wrong with this in my view, as long as there are listeners willing to adjust their listening experience to suit their tastes. Music enjoyment is after all a subjective, personal and emotional experience.
Only, out of intellectual honesty, I should not like to hear manufacturers claiming implicitely "true" rendering when in fact knowingly or not they are in fact coloring the result.
Rodolfo
AKSA said:Hi Rodolfo,
Thanks for your post.
Ah yes, thank you, this slipped by. Good point.
Perhaps you misunderstand my intent. I suggest a two stage development here; first get the engineering right, focus on low distortion, accuracy, flat response, THEN address the subjective issues within market constraints and try to make the connection between the 'coloration' we hear in a null test as you describe and the topology/dimensioning/component choice. This is the aspect which requires deep experience of the market and the practicalities to my way of thinking, although I do not decry the engineering. It's tough to get it right and clear proof is a quiet walk through the silicon crematorium.
You know, I might come across as mystical in my approach, but I have never in my design experience seen an improvement in linearity without a commensurate improvement in sound quality. This is a clear and obvious proof that accuracy is good. But while I appreciate that audio engineers stand their ground without apology I do not decry the objective approach and do not intend to fight city hall, I merely believe there is more to it than engineering, a little art, if you will. After all, pcb layout is called artwork, this is no coincidence.....
This is recognised in other fields of engineering; bridges, autos, architecture, even chemistry. I would offer that the difference between a competent design and a great one is art and passion. Why not audio? And I have noticed that even the most hard-bitten technologists here like to describe how their amps 'sound'. This is subjective, and demonstrates we are all artists at heart.
Cheers,
Hugh
Hi Hugh,
These comments are right on target, and I agree completely. Measurement and listening - beautiful together.
Bob
Folks, I'm for hot and heavy amps. That's what I like to make. I know of no better way to make the first 10 watts sound smooth and unfatiguing, than to make that first 10W class A. At higher power levels, I am not so concerned. For example, an ALL class A power amp, of greater than 350W, might require special house wiring, much like an electric stove, and special cooling as well.
However, only time will tell if certain lower heat amps actually do as well in long term listening.
When it comes to distortion, please read more thoroughly:
Matti Otala published a paper in the 1970's called: 'Correlation Audio Distortion measurements' By Eero Leinonen and Matti Otala , in the 'AES' Jan/Feb 1978, that is most definitive about this.
Another paper is 'A comparison of Nonlinear Distortion Measurement Methods' By Richard C. Cabot, preprint 1638 AES Convention 1980.
Also, what about Hirata distortion, or IIM, or PIM?
I know that some of you think that anything but harmonic distortion is not very important, but if that were so, many amps would be 'good enough' for quality listening, just like the ABX people have told us for decades. ;-)
However, only time will tell if certain lower heat amps actually do as well in long term listening.
When it comes to distortion, please read more thoroughly:
Matti Otala published a paper in the 1970's called: 'Correlation Audio Distortion measurements' By Eero Leinonen and Matti Otala , in the 'AES' Jan/Feb 1978, that is most definitive about this.
Another paper is 'A comparison of Nonlinear Distortion Measurement Methods' By Richard C. Cabot, preprint 1638 AES Convention 1980.
Also, what about Hirata distortion, or IIM, or PIM?
I know that some of you think that anything but harmonic distortion is not very important, but if that were so, many amps would be 'good enough' for quality listening, just like the ABX people have told us for decades. ;-)
G.Kleinschmidt said:
Hi Glen,
I hate to be picky, but the ExtremA amplifier does not appear to outperform my MOSFET amplifier published in 1984. At the very least, there is not enough information in the ExtremA measurements to make that statement. Check out the measurements in my paper on my site at www.cordellaudio.com. Look especially at Figures 13 and 14.
At 6 kHz, 50W and in a 20 kHz BW, ExtremA reports 0.0004% THD.
At 6 kHz, 50W in a 60 kHz BW, I report 0.00025%.
At 20 kHz, 40W, 80 kHz BW, Extrema reports 0.0006%.
At 20 kHz, 50W, 200 kHz BW, I also report 0.0006%.
At 1 kHz, by spectral analysis ExtremA reports second of about 0.00008%.
At 1 kHz, 50W, 10 kHz BW, I report 0.00017%, all harmonics and noise combined.
Perhaps this 1 kHz measurement is where you thought ExtremA was superior?
I also don't use Class A to achieve these results.
Cheers,
Bob
john curl said:
Hi John,
I agree with you. Running fairly hot bias to stay in Class A for the first several watts makes total sense. Also, given the crest factor of well-recorded music (come to our workshops at HE2007, www.he2007.com, sponsored by Stereophile and Ray Kimber), the percentage of time an amplifier spends above a few watts is fairly low unless you are playing quite loud with inefficient speakers.
I also agree that we should always pursue additional forms of measurement than just THD, and I have certainly done that. And we should always remain open to the likelihood that we may not be measuring the right thing, or the thing under the right real-world conditions. However, I've measured most of these other distortions you mentioned and there is not a lot there in most cases where the amplifier has performed well in more conventional tests. We've already beat PIM and IIM to death, and I have shown conclusively that the application of negative feedback does not exacerbate those. This doesn't mean that there isn't something else out there that we haven't figured out yet, though. The X-factor, as it were. Most of us would love to corner that cat.
Cheers,
Bob
Nelson Pass said:
You can make any amp look bad if you clip it into 4 ohms. A
peek at the distortion into 8 ohms at modest levels reveals
quite low distortion, and this is what the customers are
hearing.
Of all people, SY, you would be the most likely to appreciate this.
I haven't seen the review, so your provision of context is appreciated! What does the spectrum look like at more moderate powers?
Nelson Pass said:
You can make any amp look bad if you clip it into 4 ohms. A
peek at the distortion into 8 ohms at modest levels reveals
quite low distortion, and this is what the customers are
hearing.
Of all people, SY, you would be the most likely to appreciate this.
This is no clipping (just lame excuse
)