Need help understanding tube wpc

11-22-06: Sean “If it sounds good AND measures good, you've probably got one helluva good sounding component and / or system”

As opposed to it sounds good but measures bad then you have a bad system? Sorry, I cannot agree with that. Some of my amps have THD numbers as high as 3%, but can reproduce piano recitals with more realism than anything I have ever heard, and believe me, I am intimately familiar with piano.

Measuring is probably very useful on a production/assembly line, but I have never found any correlation between measured numbers like THD and what the amp sounds like to my ears. In fact have heard amp with excellent THD number that are useful only as doorstops. I know, I own a few amps like those.

There is only one measure that determines how a component sounds like - your ears. In my experience the folks let their ears be led by measurements have the least realistic sounding systems (read, total crap sounding systems) out there. And yeah, I have heard many of them too.

Regards
Paul

As i've mentioned before, you have to look at ALL of the pertinent specifications on the whole and understand how the results were achieved i.e. specific test methodology used. Singling out one spec on ANY product in the world won't tell you ANYTHING about how well it works in ANY given situation, let alone on the whole or universally. Audio components aren't any different. Sean
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Pauly, No, no:

As opposed to it sounds good but measures bad then you have a bad system?

Not at all. You surely know the quote: "if it measures well and sounds good -- it's good. If it measures bad and sounds good -- you're measuring the WRONG things" ;)
Cheers

"After all, musical peaks are voltage driven, not current driven."

In the world I live in, musical peaks being reproduced by a power amp produce power, not merely voltage. Voltage in a speaker cannot exist without current and this is inviably defined by Ohm's Law and the Power formula (Power=Voltage X Current).

So- a musical peak delivered by a power amp has a voltage component- *and* a current component. Since the peak represents a peak in power as well as voltage, current must therefore be peaked also.

The idea that the peak is voltage driven comes from the Voltage paradigm I've mentioned in a few threads here. What I've not mentioned is that paradigm is actually that- a paradigm, and not one based on reality. It is in fact an artifact of the 50s and 60s when transistors were making their way into audio. A central precept of the Voltage paradigm is the use of negative feedback (ostensibly to reduce THD); such use is in violation of the rules of human hearing which we all subscribe to by default.

The violation, for those curious, is the addition of odd-ordered harmonic content that negative feedback brings.

A curious artifact of the Voltage paradigm is that nothing but voltage matters in the response of an amplifier. Another is that 'voltage source' amplifiers are also defined as 'high current'. Yet another is the idea that speakers are 'voltage driven'. English speaking people will note some contradictions.

The Power paradigm aims to correct these oddities. First, *all* speakers are power driven. All power amplifiers produce power. 'High current' does not exist for musical reproduction without the generation of power, and the same is true of voltage. In this way, the power formula and Ohm's Law are satisfied within the conversation of power amplifiers and speakers and at the same time the meanings of English words are also satisfied.

Within the conversation of this thread, the issues relating to why tubes are somehow able to produce more *usable* power when their total power is less than that of transistors is easily revealed by the Power paradigm, which has it roots based on the rules of human hearing, rather than a thought model conceived to sell transistor amplifiers in particular.

The answer is that tubes generate power in a way that satisfies more of the rules of human hearing than transistors do. For example, SETs get their dynamic punch out of their harmonic generation: odd ordered harmonics are masked by even orders, so while the amp sounds lush, the odd orders are triggering the human ear to hear dynamics on peaks. It is an illusion.

Other, lower distortion tube amplifiers still manifest a greater percentage of *usable* (musical) power by the simple use of components that are inherently more linear than transistors, and usually with less stages (meaning less places for things to get messed up), objectionable distortions are minimal, resulting in little or no feedback being required for the amp to do its job. Thus the human ear is not *as* offended, and the bottom line is more of the amplifier's power generated can be used for meaningful musical reproduction.

In the Power Paradigm the rules of human hearing are not ignored so an amplifier can measure well and sound good too because the pertinent specifications that are important are the ones that get measured.

In the Voltage paradigm, as Pauly points out:

"I have never found any correlation between measured numbers like THD and what the amp sounds like to my ears. In fact have heard amp with excellent THD number that are useful only as doorstops."

-that there is no correlation between specs and sound. There is a huge disconnect here! The Voltage Paradigm seems to equate to the Emperer's new Clothes. After nearly 50 years- *that* would seem to be a little old :)

This is simple Ohm's Law. One can try to make it as complicated as they like, but it is actually just as simple as it sounds.

The amount of current needed in the circuit is dictated by the impedance of the load at the frequency that is being reproduced. After that, it's all a matter of whether or not the amplifier can swing enough voltage in time to keep up with the amplitude of the signal as it changes on a dynamic basis.

Since we've already acknowledged that high current capacity is not as necessary as most would think with reasonable speaker loads, the only reason that an amp would clip has to do with running up against a limited voltage capacity and / or the inability of the circuitry to slew fast enough to deliver the voltage required. Both result in clipping, whether it is due to limited headroom and / or a lack of speed.

With high rail voltages, high current capacity, high speed / wide bandwidth and good circuit stability, you can drive any load that you want with reasonably low levels of distortion. If you limit even just one variable in the aforementioned list though, the versatility and performance potential of the circuit is drastically reduced. This dictates more careful matching of the associated load ( speaker and speaker cables ) to that of the performance limited amplifier.

Since all amplifiers are limited in one way or the other to some degree, and no speaker is purely resistive with a higher nominal impedance, some matching is always required. Having said that, the more competently designed the amp, the more consistent the performance that it will deliver, regardless of the load. Obviously, one can go to extremes coming up with radical speaker loads that might embarrass all but the most advanced amplifier circuitry, but as a general rule, these are just that i.e. extremes and not the norm.

If speaking of extremes, anything is possible and specifics must be mentioned if we are to have any type of meaningful conversation. I have strictly been speaking in general terms, as i've not seen any mention of specifics in this thread. Sean
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PS... The fact that Ralph and i are "debating" should tell you folks quite a bit. That is, even though we both find many of same attributes very desirable i.e. wide bandwidth, high speed, reasonably low distortion, low negative feedback, high stability, high bias circuits, etc... there is still plenty of other things for us to disagree about. This is one of the reasons there are SOOOOO many different products out there with different designs.

As can be seen by our responses here, most of this boils down to what the best way is to achieve all of those goals simultaneously without having to cut a lot of corners to get there.