Need help understanding tube wpc

What the specific test results that D. Edwards linked to tries to point out is that many ( NOT all !!! ) tubed designs typically sound "richer, fuller & airier" because they are generating TONS of harmonic distortion.

These harmonics tend to make "sparse" sounding digital recordings sound more natural, hence their ability to not only "warm things up" due to the aforementioned lack of bass control / current output, but also to "breath life into" these recordings. They do this through emphasizing all of the harmonic overtones that may / may not have been present originally.

If you look at the Halcro vs the Yamamoto's spectral content, the Halco produces the primary signal and is -100 dB's down by the second harmonic. The Yamamoto on the other hand, is only about -40 dB down. This means that the Yamamoto is producing 60 dB's more output than the Halco at this point, let alone WAY more output across the entire spectrum. It does this at any given time or amplitude. Bare in mind that the Halco is doing this at 100 watts of output whereas the Yamamoto is at a watt or less !!!

Quite honestly, this is NOT a very fair comparison, but it does make a point. Using a poorly designed and possibly misadjusted ( read the text ) SET tube amp to compare to a high negative feedback SS amp just isn't fair or right. Maybe as an example of what is possible on both extremes, but not as a general example. Most designs are going to be somewhere between these two extreme examples.

On top of that, i really don't think that anyone shopping for something along the lines of the tubed Yamamoto ( rated at 2 wpc ) is going to be comparing that to the Halcro. They are completely different design approaches producing very diffferent sounds and system compatability issues. Whereas the Yamamoto might sound "larger than life" due to all of the spurious harmonic distortions added, the Halcro tends to sound thin, sterile and lifeless. Most of that is probably due to use of too much negative feedback.

Whereas the Yamamoto is a prime example of why some people refer to tubed audio gear as "distortion generators", some would say that the Halcro is a prime example of why some categorize SS gear as being "unmusical, lifeless and sterile". While one could be said to be "more technically correct than the other, it all boils down to system synergy and personal preference. After all, the bottom line is building a system that you can listen to and enjoy the music without being fatigued, annoyed or distracted by the gear itself. Some do that with tubes, some do it with SS. Some use a combo of the two, looking for the "added harmonic richness" of tubes with the speed, focus and authority of SS. Whatever you choose to go with, just make sure of one thing. That is, it makes YOU happy, as YOU are the one that has to use and listen to YOUR audio investment : ) Sean
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As usual, Sean nails it!

There is NO reason that an SS amp couldn't make use of very high rail voltages like that of a tubed amp. I've mentioned before that the amp with the highest rail voltages and greatest current capacity would be the most universal in application, so long as the rest of the circuit was fast and "sounded good". Sean
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PS... Whereas tubes are primarily a "voltage device", transistors are a "power device", hence their ability to double down when properly designed. Having the extra current capacity doesn't necessarily make up for the extra voltage capacity that most tubed designs bring with them.

"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!

Watts are watts, whether ss or tube. How loud an amp can play without objectionable distortion (to the ear) is related to how gracefully it overloads. Tube amps are better in this in that they use less negative feedback. If the same excessive feedback was applied to a tube amp as typically used in ss designs, the overload characteristics would be just as bad if the amp was dc-coupled and far worse if ac coupled as most tube amps are. Fortunately, engineers have not been able to apply large amounts of negative feedback in tube amps because phase anomalies in the output transformer won't allow it.

Of course, lower amounts of negative feedback results in higher output impedance of the amp, resulting in measurement specs gurus freaking out.

David Berning