Audio advancement - why?

Undertow said:

Advanced audio today has to do with cheaper, better, faster, more reliable ways to keep it in your house more than anything, along with heat and efficiency, reliability.

I think this is the answer in a nutshell. I don't think the early engineers said "let's develop SS because it sounds better." But, rather, the bean counters told the engineers to develop a way to produce electronics faster, cheaper and with greater reliability.

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.

Atmasphere - As far as I know class D amps enhance a little bit even harmonics (being slightly tube-like) and not the odd ones. It depends also on output configuration - from what I've heard full bridge amps (Icepower) sound more like very good tube amp while half bridge (Hypex) sound more like very good class AB. Tube amps have capacitors and transformers in the signal path - serious limitation in my opinion.

Eldartford - Early SS amps that won battle with tubes had THD in order of 0.00001% and tons of TIM thanks to insane use of global negative feedback. The problem was that TIM was discovered in 70s'. In really bad case output transistors are momentarily overdriven and stop responding for a moment after transition since charge at the junction is trapped and takes time to get out of the saturation. We don't hear tiny gaps in sound because our brains fills them but it makes us tired after a while. It cannot happen in class D. As for limitation - high power Mosfets are slower and carrier frequency is often too low, limiting bandwidth (smaller Icepowers have higher bandwidth than the large ones). 60kHz bandwidth might sound enough (200ASC) but phase shift jumps to 20 deg at 20kHz. Are harmonics added properly? Mosfets are getting faster and stronger every year and in near future class D will improve even further.
Today's class AB amps have gain before feedback often around 4000 while class A amps have gain of few hundred. I would rather have more THD and less bandwidth than TIM and blown-up upper odd harmonics - but good THD and bandwidth spects sell amplifier.

The way I understood the OP's question (or maybe the question I want the answer for) is why hasn't anyone built transistors that can sound as good as tubes to the ear? I don't think it's the matter of technology today, as we pretty much understand how transistors and tubes sound different. I don't think it's economics either. Imagine iPod with sound as good as good tube headphone amp. I bet whoever that can make transistors with tube sound will make a lot of money.

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.