Grey,
Thanks for your post; gracious, a measure of the man no doubt.
I think we agree; there is no finer voltage amplifier than a triode, and no better current amplifier than a bipolar transistor. The trick is to use hybrid, to exploit both.
Distortion is spectral. Its perception is psycho-acoustic. To narrow it to a THD or IMD figure is off target, like IQ. High order sucks, Low order can be quite nice in small quantities. Transistors when switching abruptly produce a spray of the former; tubes, when gracefully handing over the musical baton, produce almost no artefacts, and thus sound great in Class AB.
I believe we should design tube gear with just the right amount of low order distortion. It sounds more 'natural', in the same way that no one goes on TV without makeup. Here's my take on this..... (ready???)
Microphones are highly directional, even the omnidirectiona ones. What is not understood well is that they are not particularly linear, and often register different frequencies erratically. Put another way, they can de-emphasise certain frequencies, just as speakers do. Inevitably, this changes the spectral distribution (cf. harmonic structure) of the sound, and our ears hear it. It comes across as slightly dry, a little lean, lacking in fullness, or emotional communication, if you will.
The vacuum tube amplifier adds a little H2 and H3. These are both musical, particularly H2. This adds in some of the harmonic richness lost during recording. Ergo, you hear something which sounds more 'natural', even though the harmonic additions must surely differ from the original.
This theory is reflected in the wide variability of modern recordings. Mike placement is crucial, and the type of microphone is important; it is very significant, in my view, that the best of them are the German Neumanns, which all feature an integrated vacuum tube.
So that is the reason I like my vacuum tube circuits to add a little distortion. I like it, my customers like it, and I gun for it. Not in big quantities, mind you, but just enough that people say, 'Wow, that sounds really warm and emotional!'
Your kharma is fine.......
Cheers,
Hugh
PS: Grey, your fully balanced phono stage will cancel any even order distortion, allowing only odd order to pass through. A nice, symmetrical clip is a thing of beauty on the CRO, but an excrescence to the ear. Why not go for a single ended phono design, like the OzLoesch, a design Mick Maloney and I put together a couple of years back. You can see it here:
http://www.cantech.net.au/~supra/preamps.html