solid state vs tubes

Mapman- I won't speak for Ralph but I think you are missing something important here. We are not talking about an amp that is filtering or transforming anything. The issue here is that, supposedly, we perceive certain kinds of distortion (can't remember if its odd or even harmonics) as more harsh or objectionable than others. So, (to make up an example) 0.10% distortion of those harmonics sounds "worse/louder" than 1% distortion of those to which our "ears" (actually brains, I think) are less sensitive. Remember the numbers are made up and I also believe that even within the odd vs. even harmonic dichotomy, there are certain specific harmonics to which our ears are more sensitive.

I only say "supposedly" because I don't have any independent knowledge of the science nor am I an auditory physiologist or experimental psychologist. However, this explanation is consistent with what I remember from my long ago undergrad days about differential response to various kinds of stimuli. This also jibes with what I have heard w my own ears; that ss amps that measure 1X% THD do not, in many cases, sound as good as tube amps that measure 10X% THD.

If your hypothesis is that minimizing THD is an important design goal for an audio amplifier, then many would say that, based on their listening tests, your hypothesis cannot be experimentally verified. That statement does not deny that minimizing distortion is not an important design goal, just that minimizing THD (which is measured in a very specific way) cannot be shown to be an important design goal.

Another way to think of this is that it may be a case of "if your measurements don't match up your experience, maybe you're measuring the wrong thing." In this case, measuring THD may not be the right thing. I think Ralph would suggest a weighted measurement that assigns the most "weight" to those harmonics to which we are most sensitive. Call it WHD (Weighted harmonic distortion) or what have you. The relative weight assigned to each harmonic would have to be determined experimentally, in order for this concept to be applied in practice. When you think about it, THD is actually a specific type of WHD, in which the weight is "1" for each harmonic.

I'll stop now before I dig myself in too deep.

Swamp,

It seems much of the argument revolves around how amps distort, in particular how they distort when clipping occurs.

My understanding is that no amp should normally be run in a manner where clipping occurs. If it does occur, then a different and better suited amp for teh application is needed.

What happens when clipping is effectively taken out of the equation with SS? It seems to me that most issues I detect with GOOD SS amps sounding harsh or distorted can be attributed to clipping occurring or some other abnormal operating scenario that perhaps affects transient response, not a normal one.

There is a technique in image processing called contrast stretching. Essentially it means if you clip off the extreme bright and dark extents of the image or picture, you can then stretch out what remains and often show subtle contrast details that are otherwise not apparent. Seems to me soft clipping as found with many tube amps and even some SS, operates similarly. Peaks are clipped in a softer manner that is more digestible to the ear. That allows volume to increase to higher levels than otherwise. Now more subtle variations can be heard in the rest also.

Now take clipping out of the picture by using an amp/speaker combo capable of achieving this at realistic listening volumes. Peaks go louder sooner (though are not cliped or distorted necessarily) and, ouch loud things can hurt now perhaps sooner rather than later because, hey those peaks are loud as they should be. But you now may need a really good ss amp with excellent resolution and detail in order to actually hear the subtle details because, hey things are not louder overall now so subtle differences in teh sound are harder to discern, especially if you do not have good ears and or a very quiet listening environment where what is played can be clearly heard.

Am I off somewhere in describing things this way?

As a corollary, here are a few factors that might push one into the stereotypical (no pun intended) soft clipping/tube amp camp rather than the stereotypical SS one.

1) recordings must be played too loudly in order to hear subtle details (increasingly common these days compared to past with many modern loudness wars recordings)

2) hearing/ears not what they could or used to be (typical as we grow older)

3) too much background noise to discern the low level details that might be heard otherwise

Please not that I do believe that, as Bob Carver seemingly demonstrated, SS amps can tweaked to sound like a tube amp if you have a way t accurately measure the differences and you have tthe knowledge to know what amp parameters or characteristics need to be changed to accomplish the goal.

As a consumer, the trick then is to do you homework and find a SS amp that plays better in this scenario than most S amps, and more like typical tube amps.

Mapman, I am **not** talking about clipping, although it is true that in clipping, tube amps generally make less odd ordered harmonics than transistors do.

What I am talking about is the fact that when you use feedback to control distortion, the price of the feedback is distortion of the loudness cues (5th, 7th and 9th harmonics). Not by much, but as I mentioned before, 1/100th of a percent is audible. It seems crazy to think that the ear is that sensitive, but after all, it has to be sensitive to *something* and this is the mechanism that we use to determine the volume of a sound! So when you see amps with very low THD, its likely that this mechanism has been interfered with.

The result: the SS/tubes controversy since SS amps usually use a lot more feedback than tubes do (which can be built with no feedback at all)- IOW tubes more closely mimic the rules of human hearing, and so make much less of these particular harmonics, even though they often make more of the lower harmonics (which the ear finds less objectionable, though they are often credited with the 'tube sound').

Its not so much that I prefer tubes, what I really prefer is amps that don't violate human hearing rules. So that is an amp without feedback, more than it is tube or transistor.

Now, without feedback, it might be better to have either a higher impedance in the speaker and/or a flatter impedance curve, but if that is the price to be paid it seems small if it is the difference between something sounding like a stereo and something sounding like real music.