Need help understanding tube wpc

In AC circuits there is often an inductive nature that can result in current lagging behind voltage. So it is true that current may not be peaked in all cases of loudspeaker; the more 'resistive' the speaker (i.e. magnetic planars, Avalon) the more the current will be peaked with the voltage.

Nelson Pass wrote a very interesting article in Audio Express about 2 years ago that offers some interesting insight into the issue of 'high current'. I agree with his conclusions, although it would be easier to understand if his language were not part of the Voltage Paradigm conversation (although for those who only understand the Voltage paradigm, his text is a nice introduction to some very real issues!). His more recent designs are clearly based on Power paradigm concepts.

I agree that Sean and I probably do have similar concerns regarding amplification! -despite the fact that we (apparently) have very different ways of going about it.

I prefer an amplifier with both wide bandwidth (I play bass so I need good 20Hz square wave response to be convinced) and low distortion if I can get it without putting a sheen or hardness up top. Having done a lot of live recordings over the years I have to say I've gotten picky and have yet to hear an amp with negative feedback that sounds right (although there was a time when I thought all that stuff was just fine- my personal victory over the past is to have found the breakthrough results that left that behind).

I do recommend to any audiophile who is trying to create a reference-quality system to start with a set of condenser microphones, an Ampex tube recorder (I use Neumann U-67s and an updated Ampex 351-2) and some living musicians. Create a library of recordings in different venues; very qucikly you find out what a large variance exists between tube and transistor playback!! Its great to spend time at live concerts but you are powerfully in touch with what is happening when you also have decent recordings of them!

I hope y'all had a great Thanksgiving!!

"The biggest problem with tubed gear is that it typically lacks current and is bandwidth limited, both on top and bottom. The lack of current is what gives most tubed gear that "round, tubby" bass that many folks dislike. At the same time, this "added warmth" tends to "fill out" many of the leaner digital recordings that we hear. The limited bandwidth up top tends to soften the treble response, making hard, bright and edgy digital sound smoother and more listenable." [sic]

This statement is patently untrue, but is a very common misconception. There are tube amps with bandwidth to 100KHz and there are tube amps with LF cutoffs as low as 1Hz at full power. Some of these are the same tube amps. So bandwidth is clearly *not* the issue.

Similarly, lack of current has nothing to do with this either. Ohm's Law (which is inviable, BTW) reveals that a shocking (no pun intended) low amount of current is needed to drive low impedance speakers to quite high powers! The 'high current' mindset is an outcome of the introduction of large amounts of feedback in transistor amps, which is one of the major reasons that SS amps have more odd-ordered harmonic content than tubes.

In fact the issue of tube vs SS power does have to do with the rules of human hearing- which audiokinesis outlined earlier. Humans are sensitive to odd-ordered harmonics and transistors make more of those than tubes. To get around the problem you have to have a very big transistor amp so you don't come anywhere *near* clipping.

The idea of voltage rails having something to do with this is incorrect also. The voltage 'rails' merely determine how much power the amp will make- tube *or* solid state- it does not describe headroom at all. As a specification, headroom is more a function of the class of operation (class B amplifiers having the *most* headroom), but it turns out that class A amplifiers carry more authority, and for their size tend to behave as if they have 'more power'. What they *really* have is more *usable* power, and that is what this thread is all about- how much *usable* power the two technologies have.

My experience has been that in general, a tube amp will have the same amount of musical *usable* power when it is between 1/10 and 1/4 the power of a transistor amp. Variables that throw this generalization off are class of operation ( for example, a class A transistor amp will have more *usable* power), elegance of construction (don't expect a $500 SS amp to do what a $5000 SS amp of the same power will do) and the like.

Definitely muddy waters!

"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 :)