It's not hard to imagine a scenario where expectation bias, aesthetic preference and nostalgia for the industrial era, etc., creates a market.
But yes, I'm hoping to hear my friend's Little Dot soon. I'm still curious as to what kinds of distortion correlate to a "smoother" sound or increased soundstage, etc. Doesn't being out of phase "compress" a soundstage?
You're thinking of phase as a binary choice (in phase / out of phase); when you have one channel "out of phase", like when you connect the wires backwards on one speaker, what you actually have is all frequencies out of phase by an equal 180 degrees between the channels. This causes sounds with long wavelengths that are common to both channels (bass) to cancel out, which is why the bass goes away, and in general messes with our direction perception at higher frequencies. The usual effect is that things sound very odd, you can't locate where anything is, and sounds that should be located in the center sound almost the opposite - like they're
NOT in the center, but you can't figure out exactly where they
ARE. (it usually doesn't "compress" the sound stage; rather the opposite, it sort of shreds it.)
The reason that this happens is that our brains use the phase relationship between a given sound in the two channels as one of the important cues for determining location. If the phase shifts between channels are somewhat less than 180 degrees, or if the amounts of signal involved aren't equal, and if they vary with frequency, you can produce all sorts of alterations in the perceived sound stage. (This is how all of those cool "surround synthesizers" work - by carefully faking the phase shifts normally caused by differences in source location to trick your brain into hearing sounds coming from different locations. Differences in amplitude are one major cue, and the next most important one is differences in phase.) One common (and simple) trick is to take
just a little bit of the left and right channel, invert the phase of each, and add back into the other channel. Doing this with a small fraction of the entire signal tends to make the sound stage seem wider and "push" some sounds "out past the left and right speakers". Doing it selectively with only certain frequencies, or varying it by frequency, tends to "spread out" the sound stage (this is the technology behind the Carver Sonic Holography process - among many others).
While doing this in a carefully controlled fashion can produce specific results, simply randomly shifting various frequencies can sort of "swirl the sound stage around", in sometimes interesting ways - which is why, when you apply a matrix decoder (which is mostly phase-based), to stereo sound, it often creates "synthetic surround" - because the phase shifts used by the decoder interact with the phase differences in the original recording to produce shifts in the perceived sound stage. (The decoder "decodes" the random phase shifts in the source material as if they were actually information encoded there.) However, when something like an output transformer, or a too-small coupling capacitor, introduces some frequency-dependent phase shift, the result can be a sort of subtle rearrangement of the sound stage.
Many tube devices, some more than others, also tend to produce a lot of second harmonic distortion. (If you can't hear the distortion, then it doesn't matter which harmonics you aren't hearing; however, if there is enough distortion to hear, the different harmonics produce different audible results.) Third harmonic distortion, which solid state amps tend to produce a lot of when they clip, sounds harsh. Second harmonic distortion sounds more mellow. When there's significant second harmonic distortion at midrange frequencies, it can actually make vocals seem clearer and more intelligible; and adding second harmonics at higher frequencies makes them seem to have "more sparkle"; and adding second harmonics to very low bass, especially in situations where the speakers or amp can't produce enough of the primary frequency involved, will make it sound like there's more bass. (Notice how all this coincides with the terms people often use to describe the way tube equipment sounds.)
Most tube devices also have what's called "a monotonic distortion curve" - which is uncommon in solid state devices. What this means is simply that the distortion increases more or less linearly with loudness (the louder you play it the more distortion you get). Solid state equipment usually does
NOT act like this. In a typical piece of solid state equipment, the distortion remains inaudible low at all low to normal volume levels then, at some specific point, jumps up suddenly as you approach clipping. Interestingly, our brains usually associate distortion with "loudness" (which is why a 1 watt table radio can seem to be sooooo loud).
Now, remembering this, think about what happens when you play a typical 15 watt single ended triode amplifier and an "equivalent" solid state amp. The triode amp puts out 1 watt @ 1% THD and 10 watts at 10% THD; the solid state amp puts out 1 watt @ 0.005% THD and 10 watts at, perhaps, 0.01% THD. Because the distortion produced by the triode is audible, and becomes more audible at higher levels, it tends to exaggerate the loudness difference between them. (Even though the actual difference in loudness between 1 watt and 10 watts is a fixed, the
perceived difference between 1w/1% and 10w/10% is greater than the perceived difference between 1w/0.005% and 10w/0.01%; because the higher distortion at 10 watts makes it seem proportionally louder than it really is; this makes the music you're playing sound "more dynamic" on the tube amp because, even though the dynamic range measures the same, we perceive it as being greater.) This is almost certainly why many people "hear" low powered tube amps as "sounding more powerful" than their ratings would suggest - it's a sort of "psychoacoustic dynamic range expander".
(Note that, while both of these effects may sound pleasant, and may even improve the listening experience for some people, they are technically inaccuracies - aka distortion. Incidentally, there are several pieces of studio equipment, and plugins for modern DAWs, that allow you to deliberately add or "inject" second harmonic distortion, used for deliberately producing the effect I described.)
