Power output of tube amps compared to solid states

"Do tubes have the same "advantage" in preamplifiers?"

That's a good question! For many like me with tube-unfriendly speakers, the pre-amp (and source perhaps) are the practical places to introduce tubes.

I love my ARC sp16 tube pre-amp, but I do wonder if a good SS pre-amp could also deliver for similar cost or less once the speaker/amp optimization has been achieved.

I think they do. It would be really tricky to build a zero-feedback transistor preamp. With tubes you can do three stages of gain between the LOMC phono input and the line out, I doubt that the same can be said of transistors, at least, I've not seen any so far.

I have an additional comment about distortion that Joe mentioned- that of, shall we say, 'dynamic distortion'. Its my opinion that we need some sort of distortion test that uses a non-repeating waveform similar to what you see in real music. What Chaos Theory is saying about this is that sine waves represent a stable state in an amplifier circuit that might otherwise have chaotic response. BTW Norman Crowhurst pointed this out 50 years ago in his writings about negative feedback. Chaos Theory really seems to point to the idea that negative feedback is a destabilizing factor in amplifier circuit design, in fact, going so far as to call it non-linear.

This seems to fly in the face of traditional theory, where negative feedback occurs as something to increase linearity. But what we find by its application is that the energy of the distortion (nice calculus segue here BTW) is not changed at all- it is instead spread over the spectrum as a harmonic noise floor injected into the circuit's output. In addition, in-harmonic distortions are created due to inter-modulations at the feedback node.

The way the ear deals with this is interesting- our ears can penetrate natural noise floors like hiss or the wind blowing by about 20db, but can't do the same with this harmonic noise floor, which thus masks detail that exists below it. This is one reason why zero feedback circuits tend to be more spacious.

There are many here much more qualified than I am to answer these questions, but, it would appear to me that it really wouldn't be an issue with preamp. I would think most pre-amps have more than enough steady state power necessary to drive a power amplifier. Head room and it's duration wouldn't be a necessary consideration.
Atmasphere, would you consider a passive pre a ss device? If so, where would the feedback be there? It seems as though some of your arguments are based upon opposing theories rather than laws.

Trelja, thanks for the kind words.

Unsound, are you referring to the Threshold S/500? If so, there must be some inconsistencies around what is meant by "double its rated power for several minutes" . . . because I remember this amplifier having rather conventional headroom characteristics (but it's been at least 15 years since I've worked on one, so I may be wrong). To clarify, what I'm terming "dynamic headroom" will generally manifest itself as the ability to generate additional unclipped short-term voltage and current beyond the steady-state clipping power.

If "short term" means several minutes . . . then the limitation that keeps short-term capacity from being long-term capacity is almost surely thermal dissapation, not energy storage or output device current-limiting. The only SS amps that I can think of that exhibit this characteristic are what I would call "asymmetrical class H" operation, like the old NAD "power envelope" design. This works by having the amplifier operate from lower-voltage rails most of the time, but for large-signal peaks there is another set of commutating transistors (like conventional class G or H) that pulls the voltage up to a higher rail, and then keeps it there for a fairly long time-constant. The reason why it doesn't operate at the higher rail all the time is purely thermal . . . so I would actually consider it this design a higher-powered amp with thermal limitations, rather than a lower-powered amp with lots of headroom. But that's purely terminological I guess . . .

Do tubes have the same "advantage" in preamplifiers?

No. Tube preamp stages almost universally operate in Class A, so they have a steady-steady current draw regardless of the output level. Consumer preamps also usually operate into high-impedance loads (little current required), and virtually never have output transformers (to perform the power-supply impedance transformation).

In a headroom sense, tube preamps do operate from much higher-voltage rails . . . and even though they tend to have more linearity problems as they approach their voltage limits, there's still usually a certain headroom advantage. But this is likely to only be an issue for something like a professional mic preamp, seeing the raw feed from a large-diaphragm dynamic mic that's three inches from a kick-drum head.

Atmasphere wrote:

I have an additional comment about distortion that Joe mentioned- that of, shall we say, 'dynamic distortion'. Its my opinion that we need some sort of distortion test that uses a non-repeating waveform similar to what you see in real music.

I take it you're familiar with Matti Otala's 1972 AES paper that started the whole TIM measurement thing, and the huge number of papers and followup over several years in response? Do you feel that there are aspects of this issue that need further research?

BTW Norman Crowhurst pointed this out 50 years ago in his writings about negative feedback.

I take it you're referring to Crowhurst's two AES papers from 1957 and 1969. There are several historical things to keep in mind with how amplifiers were rated in those days, and most of what Crowhurst seems to have been concerned with in the 1957 paper is practical problems with the use of negative feedback as a method for reducing costs. He also makes limited to "regenerative distortion" (feedback making distortion of the distortion), but much of the theory here is very vague.

If we look at the perception of simply how powerful the amplifier is . . . I think it breaks down over tube/solid-state lines much more than global-NFB/no-global-NFB lines, and I personally don't feel that negative feedback has a whole lot to do with it.

Now for subjective sound quality and measured performance, feedback is a huge topic, and I'd love to get some discussion on these papers and their theory!! But let's start a new thread for it . . .