Rainy Day Musings

Good core point -- if I followed, you're saying that since harmonic distortion products are mathematically identical in frequency to instrument overtones, the signal cannot be decomposed into "wanted" and "unwanted" harmonics by any downstream stage — including your ears. The distinction is purely definitional, not physical.

Here's what your post left me sitting with: if your tube preamps measure below 0.1% THD, you're essentially arguing that the subjective improvement you hear over the Mark Levinson cannot be attributed to distortion added by the tubes — which strikes me as true.  That leaves the question open rather than closing it in favor of either camp. Have you considered that the difference might be in output impedance interaction with your downstream components rather than anything the distortion figures would reveal?

@kevemaher - I live in Northern California too and thoroughly enjoyed yesterday's rain!  

That's quite a blanket statement about tube preamps! I've had a number of tube preamps and none of them run as hot as my SS power amp; they don't run 'hot' at all, unless you touch the tubes themselves.

As for 'stability', while it can marginally improve over 20 minutes or so, they also sound just fine right away, and I can enjoy the music without worrying about warm-up time. 

All musical instruments would sound exactly the same if it were not for the characteristic harmonics/overtones each produces. It's said that tube amps tend to produce even-order harmonics which we find pleasing, and increasing the richness or lushness of the instrument being reproduced. Yes, they lie to us when they do that: it would sound different if the instrument was in the room with us. Perhaps instead of "lie" I should say they embellish the sound, as that seems more respectable.

This is why I keep several tonearms and cartridges. I know that Statement3 lies to me—sorry, embellishes the sound—but I like it. The Hyperion shows me something much closer to the original performance, but sometimes I want the lurid version. I used to have a pair of SET amps that told me pleasing stories too. Having had them I can't find solid state satisfying anymore, but I have compromised with push-pull power amps. It seems that I'm not so much worrying about whether harmonics are on the recording, or being introduced as distortion, but simply finding the right total dose to suit me.

Tube preamps have drawbacks. They run hot, are not energy efficient, need care and replacement for tubes that wear out, and need 10s of minutes to achieve stability. These seem to be better criteria for tube/solid state decisions, not distortion.

What? No, it’s like a minute, max for the heaters to ramp up. Sometimes a timed relay is used to ensure safe application of the high voltage line, and 2 minutes is the most I’ve seen this set for (a bit over the top imo). Never yet had a pre / phono tube component that needed a protracted warm-up period to stabilize or sound good. All of the "protracted warm-up to sound good" components I’ve had were due to persnickety transistors. BTW if you pop an OOP transistor, good luck getting a replacement. SS may be great for short-term maintenance costs, but tubes are generally much better for long-term maintenance. 

The feed and caring for preamp tubes is absolutely minimal IMO. It becomes a time & money sink only if you get into rolling and start seeking out vintage tubes. 

From this I must conclude that tube preamps designed to have low distortion (less than 0.1% or ???) are indistinguishable from solid state components in this category.

Yes, I think it’s a reality that tube components designed for lower distortion tend to sound "more solid-state like". The rational conclusion is that tube components sound the way they do because of their particular distortions. My counterpoint is: "but I really like it". Some will argue the kinds of distortions (high order blah blah) introduced by many/most SS components is so disagreeable that it’s a problem even at extremely low amounts - there’s probably truth to that, but when you have modern SS with so many 0’s of THD, it’s hard to argue that could be discernible at all by human ears, even if it’s the worst type.

I believe (without evidence - this is no scientific journal) the studio recording process saps some "life" out of the end product, and tubes are the best way to convincingly add back in what was lost - contrary to the "garbage in, garbage out" philosophers on these forums.

In summary: tube circuits add distortion, but I really like how it sounds. I also enjoy an occasional SS component too, but it’s never the 9 zero’s THD types that rank well on ASR. Tube power amps add even more distortion (especially at higher volumes), and I like it there too.