Only because the design sucked in the first place (*). Probably designed by a "tooobz" engineer ;-)
I have yet to see a single design that demonstrated the proper way to do a stable A-B bias.
I know how but I ain't talking ;-)
I like mixed fruit salad myself... apples, oranges, grapes, Kiwi, and maybe some Pomegranate ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Indeed they have, but those are rare and honourable exceptions, and diametrically opposed to the designs favoured by most in this forum, which appear to majotr on restricted bandwidth and high distortion. It must of course also be pointed out that what distinguishes these excellent tube amps, is that they sound exactly the same as any good SS amp..............................
They are down about 10dB typically in power response.........
Hooey, this is typical flimflam uttered by tubies because hardly any tube amps are *capable* of 0.01% distortion.
In your humble opinion.
Hamm's paper was not peer-reviewed, and it was written so long ago that it is irrelevant to modern amplifiers. The laws of physics have not changed, but our ability to manufacture excellent SS devices certainly has.
So are tube amps..........................
--
Stewart Pinkerton | Music is Art - Audio is Engineering
Worse still, Hamm considered only a very dated style of a.c. coupled common emitter transistor amplifer without degeneration and the majority of his conclusions were about its character when *overdriven * ! Simple. You avoid 'overdriving' !
AFAIK, *everything* in the JAES is peer-reviewed. I guess the peers were also tubies. Either that or they were smokin' some gooooood stuff. Maybe both. ;-)
The Hamm paper was no doubt obsolete on the day it was written, for many reasons. One problem I've noticed with it is that it compared the large-signal distortion of amplifier stages with differing gains. Since the stage gains differed, the output signals differered dramatically in terms of amplitude. Hamm thus built his case against SS on the fact that simple SS amplifier stages tend to have higher stage gain than triode tubes.
Agreed. Among the first SS test equipment to come out were audio signal distortion measuring equipment.
I'd like to find some AES old-timers and get some straight answers about how a POS like the Hamm paper made it through the JAES review process. The guilty parties are probably dead and gone by now, so the truth might be knowable despite the confidentiality of the review process.
No, eberything is NOT necessarily peer-reviewed. Engineering reports aren't necessarily peer-reviewed.
However, Journal articles are.
Has anyone here actually READ The Hamm article. It woiuld appear not, as it does NOT support any of the assertions made about. Consider the precis of the article:
"Engineers and musicians have long debated the question of tube sound versus transistor sound. Previous attempts to measure this difference have always assumed linear operation of the test amplifier. This conventional method of frequency response, distortion, and noise measurement has shown that no significant difference exists. This paper, however, points out that amplifiers are often severely overloaded by signal transients (THD 30%). Under this condition there is a major difference in the harmonic distortion components of the amplified signal, with tubes, transistors, and operational amplifiers separating into distinct groups"
Let's look at the KEY points of the article:
Previous attempts to measure this difference have always assumed linear operation ...
amplifiers are often severely overloaded by signal transients (THD 30%).
The article ONLY deals with the amplifiers topologies AT THE TIME, UNDER CONDITIONS OF SEVERE CLIPPING DISTRTION.
It makes NO claims about the operation under normal conditions. The implications are quite clear: Clipping results in audibly different output from. An early 1970's tube amplifier sounds different than an early 1970's transistor amplifier WHEN BOTH ARE BEING SEVERELY CLIPPED SUCH THAT THEY ARE GENERATING 30% THD.
The solution to the problem is NOT to by tubes or transistors. The answer to the problem is VERY simple:
DON'T CLIP THE AMPLIFIER!
Thus, Hamm's paper supports the reasonable assertion that a 250 watt sollid stats amplifier MUST sound better than a 20 watt tube aplifier when both are being asked to try to produce more than 20 watts.
Thus, Mr. Ludwig's assertions:
"Subjectively tube amps of a given specification often (not always) sound better than solid state amps of better spec. Russ Hamm proved it in 1973 with his paper which appeared in JAES"
is simply not supportable. The ONLY difference that the Hamm paper deals with is under conditions of sever clipping, which is not "always," it's not even "often" as Mr. Ludwig erroneously claims. Further, his statement:
"and it has not been contradicted."
Is similarily false, as the following citation suggest:
Monteith, Jr., Dwight O.; Flowers, Richard R.; Hamm, Russell O, "Transistors Can Sound Better Than Tubes," Vol 25, no. 3, pp. 116-120; March 1977
What's interesting is Hamm, the author of the paper erroneously cited by Ludwig, is one of the authors of this paper!
Further, the suggestion by Mr. Krueger that there is something fundamentally amiss with the article or the reviewers is similarily off the mark, because if you actually deal with the contents of the article, you find that it makes reaonable sense: solid state amplifiers clip differently than tube amplifiers, and for a variety of reasons.
I raised a specific issue which Mr. Pierce you appear to have intentially deleted from the post of mine you quoted in your attempt to make it look like I hadn't read the paper:
"One problem I've noticed with (Hamm's paper) is that it compared the large-signal distortion of amplifier stages with differing gains. Since the stage gains differed, the output signals differered dramatically in terms of amplitude. Hamm thus built his case against SS on the fact that simple SS amplifier stages tend to have higher stage gain than triode tubes.
As far as the claim that tube and SS amps have differing clipping characteristics, this is not a given. If this comparison is to be made then the amps should be as similar as possible, differering *only* in the fact that one has active devices are tubes and the other has active devices that are SS.
IOW the amplifiers being comapred should have similar or indentical coupling and impedance-matching circuitry, simliar or identical kinds of and amounts of stage gain, overall gain, and NFB, etc. Of course the amplfiiers should also be based on good design practices.
Both Graham and I have pointed out that Hamm's paper fails to be a true apples-to-apples comparison of tubed and SS amplifiers on these grounds. Even if only the clipping characteristics of the equipment were compared, then the comparison needs to be as close as possible. I see no evidence that Hamm attempted to hold the relevant parameters as close as reasonably possible. Therefore, even with the narrow criteria related to clipping behavior that is stated above, the Hamm paper should have never passed review by the JAES review board, if it was ever reviewed.
In case the meaning of my comments above is not obvious, any well-designed power amp is going to be well-biased, have good audio bandwidth and respectible amounts of NFB whether local or global.
Since the presence of audio transformers introduces many complex factors, they would likely be eliminated from the SS and tubed equipment that would be compared.
With these parameters held constant, both tubed and SS amps produce respectible and very similar square waves when clipped.
Therefore, a study of the audible significance of differences in the clipping performance of tubed and SS equipment becomes of limited signficance in an true scientific apples-to-apples comparison. Hamm's paper didn't represent good science, or good art and should have never been published in the JAES except as a an example of poor-quality work.
Yes, that was my experience. I published an engineering report in JAES (from a presentation at the LA convention) and it was not peer-reviewed. It was on a digital subject in the mid-70s, so maybe they couldn't find anyone to review it? :-)
"Don't clip the amplifier" is easy to say, and tough to do. Totally avoiding amplifier clipping under any and all circumstnaces requires either active power compression control (i.e. "Power Guard") or a really, really, really big amplifier, the very small signal performance of which is usually suspect unless the amplifier is made extremely heavy and hot and has a very high quiescent power draw. A 20 watt tube amp that pulls 50 watts at full power is more efficient in practice than a 250 watt solid state amp that pulls 80 watts quiescent and 500 at full power if either provides the same _subjective_ performance-even though the solid state amp is more efficent for each watt it puts out.
First, Hamm's article by title states "transistors _can_ sound better than tubes", which is sometimes true, not that they "always do" which we know to be false.
Either vacuum tubes or trnasistors can be used with good results. However many people still prefer to use vacuum tubes, at least under certain circumstances.
However, I have not yet read this second Hamm paper, and will endeavor to do so. It still won't make building tube amps any less recreationally rewarding, though.
Mr. Ludwig, it is clear that you're not in the least bit interested in dealing with the content of the article. You never read the article, that's apparent, and you're making a load of baseless assumptions completely irrelevant rantings.
What on earth does this load of abosolute nonsense have to do with the point? Your rantings are pointless and meaningless.
My statement was VERY simple: ANY 250 watt amp trying to produce more than 20 watts into a load is going to sound MUCH better than ANY 20 watt tube amp trying to produce 20 watts into the same load. That's what the implication of the Hamm article is. You don't even need a "really really big amplifier" for this to be true: a 50 watt solid stat amplifier is going to sound better producing, say, 35 watts than ANY 20 watt tube aplifier trying to produce 35 watts.
You demonstrated you didn't have a clue what the first Hamm article said, and now you want to enhance your already solid reputation by showing that you haven't a clue about this one either? Go for it.
That's NOT what your claim blanket claim was. You claimed that an article that you never read supported your assertion.
You've made numerous assertions, such as the operation of test equipment, the peroformance of amplifiers and the contents of articles, all clearly from a position of minimal if any experience or knowledge of the topics.
We obviously are not communicating too well. I feel like I'm in a scene from "The Misfits" (if you have to ask which one you haven't seen the movie.).
I have read the first Hamm article under discussion, "Tubes vs. Transistors". I have not read the second Hamm article and was in fact ignorant of its existence until about a half hour ago.
Let me go read it.
Frankly my entire thesis is simpler than all this: some people like to build tube amps! As with model trains, the issue of practicality is secondary. However, it is my contention that it is not a wholly onanistic endeavor-the tube amp still functions well and does a certain job with complete satisfaction.
You have made your own self contradictions quite clear. The issue is not one of communications, but expertise, or the obvious lack thereof.
No, you stated the following, quite clearly and unambiguously:
"Subjectively tube amps of a given specification often (not always) sound better than solid state amps of better spec. Russ Hamm proved it in 1973 with his paper which appeared in JAES and it has not been contradicted."
Nothing in your statement intimates anythong about building tube amps. Nothing. That thesis, as you stated it above, has been shown to be incorrect. And if you did read the original Hamm article, clearly the major point he made failed to stick, because it was all about the performance of the amplifier under conditions of severe clipping.
So what it really boils down to is not tubes vs. transistors, but transformered vs. transformerless! :-) (and all of the design pattern differences such a concept entails)
I guess it depends on what you are doing with the amplifier. In a live venue or a recording studio, where you have no idea in advance of what the signal levels are going to be, I would agree with you.
At home, level matching everything from the CD player to the volume control guarantees that my power amp will not clip until the preamp is turned up at least 1/2 way. That setting is well above my comfort level.
Actually, it's a piece of piss if you're using CD as a source, since you can set system gain to sit just below clipping for 0dB FS from the CD. That's what I do with my '50 watt' Krell.
--
Stewart Pinkerton | Music is Art - Audio is Engineering
Ever notice how many tubies also prefer vinyl? It's a whole retro thang, combined with the notion that if it involves more work and more expense, it must necessarily have higher performance.
Like entropy, nostalgia isn't what it used to be............
--
Stewart Pinkerton | Music is Art - Audio is Engineering
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