differences between tube and solid state designs

Well first of all, there are different types of solid state amps, and different types of tube amps.

Areas where different topologies produce different results mostly have to do with their distortion characteristics.

For instance, tube amps soft-clip, which is much less objectionable to the ear that the hard clipping typical of solid state. I think this is the science behind the oft-quote observation that one tube watt = two solid state watts.

Class A/B amplifiers distort in the crossover region (the amp's crossover, not the speaker's), and that's a distortion that (with most A/B amps) happens at very low power levels so it happens all the time but is most noticeable at low listening levels. Class A and Class D amplifiers do not have this distortion. [I suspect that some of the low-level articulation advantages attributed to high efficiency speakers is due to their typically being driven by Class A amplifiers which have no crossover distortion].

Now as an aside, note that there is often a negative correlation between low THD numbers and subjectively "clean" sound. In other words, we tend to prefer amps with higher rated THD! The reason is, usually those low THD numbers are arrived at through the use of negative feedback, which in effect trades off high percentages of low-order harmonic distortion for low percentages of high-order harmonic distortion. The ear finds the latter more objectionable than the former. Studies have shown 30% second harmonic distortion to be inaudible with music program material.

One disadvantage a push-pull tube amp has is its output transformer. As the signal changes polarity the field in the output transformer is inverted, and it takes some energy to do this. That energy comes from the output signal. I don't know how audibly significant this is. Single-ended and OTL tube amps do not suffer from this effect, known as hysteresis.

Zero negative feedback Class A amplifiers tend to sound the best because they have the most psychoacoustics-friendly distortion characteristics, assuming they are powerful enough to not be driven into clipping. Such amplifers can be tube or solid state. The day may come when high quality Class D amplifiers are counted in the same category, as they are inherently free from crossover distortion.

All that being said, the audible differences between amplifiers are at least an order of magnitude less than the audible differences between loudspeakers.

Duke

And that's why I don't read any audio magazines anymore.

"I think your confusing reality and realism"

The second order harmonics question was answered by the Pass Alephs and, to some degree, Plinius SA-series.

i think the differences between vintage tube amps and especially the cj mv 125 and current tube amps , excluding set amps, is greater than the difference between current tube amps and solid state amps.

i think what has happened over the last 25 years is the discontuance of an identifiable tueb sound. yes you may call it coloration. in its place, is a presentation closer to accuracy--perhaps still some audible coloration.

i have heard some current cj, audio research, wolcott, granite audio, consonance etc., current tube amps and walked away thinking... "it almost sounds like solid state. why ? "

isn't there some advantage for having designs which sound significantly different from each other so that the consumer has a real choice. the overall variation in sound today within tube designs, within ss designs and between tube and ss designs, again, excluding triode and low powered set amps
is not as great as it was 20 years ago.

Almost sounds like SS... but doesn't. Plinius and Pass? Yuck.

I just cannot go along with this notion that I hear repeated all the time, "The best tube and solid state amplifiers seem to be converging in sound."

Personally, I've more or less yet to hear a solid state amplifier that can make me happy. They just do not instill the flesh and blood into the music that a good tube amplifier can. The higher end solid state amplifiers' offer "more" in most cases - more power, more low frequencies, more high frequencies, more clarity, etc., but still seem to miss the mark for me.

For what it's worth, I'm not enamored of the direction that the high, high end tube amplifiers are going, either. From what I see, the trend is towards bells and whistles like flourescent screens and overly complex biasing and checkout routines. I have no interest whatsoever in the direction ARC and VTL are trying to push the market.

Give me a great sounding, simply designed tube amplifier, and I'll be happy. I'll make sure I have a decent multimeter and screwdriver on hand, and at somewhat of a regular interval, bias it myself. It takes a bit of work, but it's a very, very small price to pay. I haven't heard anything come along that sounds better yet. Not that I'm not willing to listen to what anyone can put forth, if there were solid state amplifiers that suited me, I'd be running one.