Audio advancement - why?

Milpai, as humans we hear in a very specific way- there are certain types of distortions that our ears don't care a lot about and there are other distortions that our ears care *a lot* about.

For example, we used the presence of odd-ordered harmonics, specifically the 5th, 7th and 9th as a means to determine how loud a sound is. This is arguably one of the most important rules of human hearing as being able to tell how loud a sound is is the sort of thing that can say whether you live or die!

It happens that tubes can make less of these harmonics than transistors usually can. There are exceptions (although they are few). To do this one would have to avoid the use of global negative feedback as a design element regardless of the circuit being tube or transistor. This is a lot harder to do with transistors (since they are not as linear) than it is with tubes (triodes are the most linear form of amplifying device known).

It turns out that global negative feedback, which is normally used to great success in reducing overall distortion (THD) actually enhances, to a very small degree, the odd-ordered harmonics that I mentioned before. Our ears are extrememly sensitive to this enhancement; 100th of a percent is easily audible and audiophiles have terms for this that you have heard before: sheen, hard, harsh, brittle, clinical, etc., all expressions of a very small amount of odd-ordered harmonic enhancement.

In case it was not clear, the point of my prior post is the fact that tubes happen to obey the rules of human hearing to a much greater degree than transistors do, hence the reason why it is so much easier to make a musical sounding tube amplifier than it is to do the same with solid state.

If you look at it from the perspective of rules of human hearing vs the use of global negative feedback, it becomes much clearer. See

http://www.atma-sphere.com/papers/paradigm_paper2.html
for more information.

Eldartford, what you say is partially true- the problem is that the distortion signature still enhances odd-ordered harmonics.

Milpai, humans *were* able to make advances in audio- and it turns out that tubes are the way to do that- appropriate technology IOW.

Actually there are transistor amps that do that, but you can count them on one hand with fingers left over. None of them employ global negative feedback- it seems that NF is a design element that has been holding advancements in audio back.

So far the Ridley Audio amplifier is the best example I have seen of what can be done with transistors. Last I heard, it made 100 watts and cost about $100,000 for a pair. There is a heater circuit for the output devices that makes the amp run every bit as hot as tubes. It is better than many tube amps I've heard.

I have yet to hear a class D amp come close, but that technology is still evolving and may yet bear fruit.

Milpai, true, we are stuck- for now. Believe it or not I would be the first to jump on the transistor bandwagon if I thought I could do it without sonic sacrifice!

Kijanki, the difference between audible enhanced even and odd ordered is something like this: with the evens, we start to hear that they are there with about 0.5 to 1%. With the odds, we are well aware of them when they are about 0.0005% or so.

The evens can be canceled by fully differential balanced operation. Its not a great benefit to have the output of the amp be push-pull if you don't do it throughout because all the gain stages make distortion. So if you operate fully balanced throughout the circuit, the overall even-ordered harmonics will be very low or non-existant.

After that you do your best to not enhance the odd orders- zero feedback, class A operation, minimal gain stages, higher quality components, more linear amplification (triodes as opposed to pentodes for example) and so on.

This, BTW, is one of the very clear 'audio advancements' that has occurred in recent years. There are tube and solid state amplifiers that use these techniques today; thirty years ago they did not exist.

Kijanki, you and I are on the same page!