Well said Tung, I was about to write up a similar explanation
It's really important when we discuss things amp and speaker related to keep tube amps and SS amps separate, lest more misinformation be spread around the web. SS and Tube amps could not be more different in the way they operate, they are in fact almost polar opposites to each other, so it -should- be obvious that the rules are quite different.
Clipping is a fine example, as has been explained here. People try to drive tube power stages into clipping because it sounds more musical, where a SS power stage should never ever be forced into clipping.
Something I'd like to drop in here is power ratings. Everyone who has dimed an 18W, or heck, even a 50W tube amp will tell you emphatically that 50W tube is FAR louder than 50W Solid State. Myself included. One of the main reasons behind this phenomena is actually to do with clipping, hence my thought to include it here.
Surely an amp rated to deliver 50W RMS is delivering the same 50W RMS as a SS amp right? If not, our fancy "Watts" and "RMS" measurements are meaningless surely? The good news is a SS amp and a tube amp rated at 50W RMS will both deliver exactly the same amount of power, so our rating system is in tact.
For the sake of this explanation I am overlooking the fact that a SS amp designed to deliver 50W will do so consistently from amp to amp and from day to day, whereas a tube amp, especially an older one, will see it's power output vary depending on your mains voltage, age of tubes and filter caps etc. Thats another discussion.
I'll also gloss over the very real effect of signal compression on perceived volume by simply stating that tube power stages compress the signal and this makes it sound louder, SS amps don't do this anywhere near as well, if at all.
Anyway, so we know both amps are capable of pushing 50W of power into the speakers, so why on earth does the tube amp sound so much louder? Well, as I said, it's to do with the way tubes and transistors clip, and also the way our ears hear.
Before I launch into the next bit, I'll explain what I mean when I refer to clipping and distortion, because again, it's confusing. Especially when us electro-nerds keep referring to clipping as part of a distortion pedal!
Distortion happens when you feed a signal (your guitar for example) in one end of a device and it comes out the other looking different. It can be a change so small we need to measure it in .0001 of a percent, or it can be a horrible screaming mess that obliterates the original signal. It's all about the original signal being reshaped in any way.
Without going into why clipping occurs, although I'm happy to if anyone wants me to, clipping is where the top and bottom of our nice smooth signal are sheared off. Because we have altered the signal, clipping is therefore a form of distortion.
A tube amp has more distortion at signal levels below clipping than a solid state amplifier. A lot of the flowery terms we use to describe why the cleans of a tube amp are more pleasant than a SS amp are really just prettier ways of describing what is actually low volume distortion. Yes, your big old Fender is actually distorting the signal long before you hear any "grit", or "growl" or "bite" or, well you get what I mean.
Incidentally, this inherent distortion is part of the reason tubes are rarely used outside the music game these days. If you want clean, linear amplification, for audio or otherwise, transistors run rings around tubes.
This tube distortion increases slowly until the signal starts to clip, and then more rapidly after the onset of clipping. You know this sound as the roar of a cranked tube amp.
The SS amp on the other hand has no such gradualism. It is almost perfectly non-distorting right up to the point that it clips, and then it clips HARD.
Hang on. I've just said that both SS and Tube amps will clip and therefore distort the signal, although they both do it in a different way, so how on earth does that make one louder than the other?
Well, in the end it actually comes down to evolution, or God depending on you point of view, because it's actually a result of how your ears work.
For reasons unbeknown to me, the human hear detects the effect of hard clipping transistors as harsh distortion, and the softer low order harmonics generated by tube clipping as musical distortion AND VOLUME.
So simply put, all that extra distortion in a tube amp at full noise is detected by your ears as volume! Something that can't happen with a SS amp. If we drive a SS amp into clipping our ears just tell us "OUCH"
So there you go. I'm not at all a religious guy so I say this in jest, but maybe this phenomena is Gods way of saying "Play Tube Amps"
