Is Mark's Kit a 6V6 completely enclosed amp or a 6550 out in the open amp? I thought he had a 6550-based beastie. . . .

Just tryin' to keep track.

The main problem I see is the Intermodulation Distortion (IM). It is generally 3.2 times that of Harmonic Distortion. So if an amp peaks at 3% distortion, the IM is close to 9.5%. If it is 5%, then the IM is more than 15%!

An example of IM distortion: a 1k and 800 signal "mixes" to produce signals of 200hz and 1.8khz. No wonder the music might seem filled out.

One can tell the quality of an amp when a "review mentions liking simple music and not complex, like orchestra. This tells me the IM distortion is very high as it really messes up the music.

Another area is the drive needed for the output signal. Alot of distortion comes from the driver and even before that. This mixes to produce higher order harmonics, although lower in amplitude, that are easier to hear.

Passive parts distortion also plays a major role in the sound. Using passive parts like carbon resistors is guaranteed to artificially "distort/color" the sound.

So the problem with an amp is much more than HD, but IM, topology, parts distortions etc.

Steve

As you mentioned, PPs can have very low distortion without any feedback.

I have to agree with Ash.. At 2004 CES, The Show, all I heard was fat with one or two thin sounding SETs. I visited those rooms several times, on different days listening to different selections.

As you say, "I don't think gross and misleading generalizations do much to advance our collective state of enlightenment regarding the audio arts..."

Steve

I think one problem overlooked with SETs (and I make them) off the top of my head is the huge change in output Z. This can easily be an 8 to one ratio, or more. As an example, the damping factor changing from 8 to just 1 over a portion of the cycle. So the control the amp has over the driver is constantly changing.

PP can also have this problem, in a different way, though to a lesser extent.

Take care.
Steve

and:
but with it's own set of harmonics

Just another way of saying, " I like the distortion spectra of a SET amp".

What I want is a means of measuring the sonic nuance which a good sounding amp has.

And on a more personal note, good amps are not limited to the SE topology.
regards,
Douglas