I completely agree with these two statements. You seem to have observed the same thing I have observed. Ralph has joined the discussion a few times on my natural sound thread to promote his new class D amplifiers while criticizing the performance of SET amplifiers. I had to point out consistently and with reference to distortion graphs supplied by Lamm of my specific amplifier pair that they are very low distortion, particularly in the loads they encounter when driving my corner horn speakers. Ralph eventually conceded the point and I wished him well selling his new products hoping he would do his marketing elsewhere.
I was not there to promote our class D. I did mention class D though, in the context of explaining how the distortion signature of the amp is its sonic signature and there are now class D amps that sound very much like the best tube amps and unsurprisingly have a similar distortion spectrum.
The Lamm, being zero feedback, is
not low distortion. It makes about 10% THD at clipping although the exact point of clipping, because of all the distortion, is a bit tricky to pin down. What I agreed to is that if you're going to use an amp like that, you have one of the best speakers for doing so, so to maximize the strengths of the amp and reduces its weaknesses. You'd do even better if you employed active subs
and limited the bass that the amp sees. You'd hear the improvement immediately.
My criticism of SETs is based on engineering and experience. I've been designing and building them (I am a hobbyist as well as an engineer) and auditioning other examples since about 1991 when Joe Roberts (RIP) of Sound Practices first started promoting them. I've never seen one work as well as other tube amps if both amps were on a loudspeaker on which they were both comfortable. So that's the anecdotal side of it.
The engineering side is vast! Bass is a problem on several counts, starting with the fact that most SETs require a 'cut core' in the core of the output transformer to prevent the DC current of the output tube from saturating the core of the transformer- this to prevent distortion on that account.
The problem is in doing so the inductance of the transformer is reduced. You need inductance in the transformer to make bass. So what happens is the
load line of the tube, which as you see at the link, which should be a straight line,
becomes elliptical . When that happens distortion takes off and its hard on the power tube as in some points of the operating point thus created, the tube is trying to drive something that looks like a short.
This is why SETs sound a lot better with light jazz or chamber music, but fall apart if you put anything with deep bass into them. For that reason, the people who have the most success with SETs use a different amp to make the bass and often use a crossover to prevent bass getting into the SET. I can go into a number of other problems and have elsewhere as you pointed out: you get the point.
Two of some of the more vociferous advocates of SETs I know of both use this approach as they are very well aware of this problem. One is active on this forum. I have noticed that there's not a lot of engineering talent when I get into these conversations about SETs. Most people don't like to hear about the flaws of the technology in which they have invested! I'm sure this hasn't helped me.
I can't help but notice in writing this that I've not been taking my own advice regarding reviews. If I were I would just remain silent about SETs. So some might see that as hypocritical and perhaps it is. So I might have made a mistake. The thing is though, I'm not a reviewer, I'm an EE.
For all those who think bad reviews
do have a place in high end audio, some of you who are on this thread and have given me some heat on this, what do you think I should do about my knowledge of SETs? Should I be honest about their failings or just be quiet?
So I tend to look at things differently. For one thing, I've noticed that the way amps make distortion affects how people perceive the amp; that quite literally the distortion spectrum of the amp and how that changes dynamically with power output (and to a limited degree the output impedance of the amp and how that interacts with the loudspeaker) is the 'sonic signature' of that amp.
Its the difference we hear between amps.
Once you understand that fact, as a designer that opens an access to designing equipment to be musical rather than just specs on paper. Its no longer about having to have a certain
kind of amp to get a certain
kind of sound. Of course, keeping distortion down is important if you want to hear greater detail; but what distortion you get should be of the kind to which the ear is the least sensitive, which are the lower ordered harmonics, the 2nd and 3rd.
I get the charm of an SET. Its very much like hopping on a 1940 Indian 741 Scout and making your way down some quiet country roads. Who cares that you can go a lot faster, take the turns with less worry, use less gas and oil doing it and make less noise with greater comfort on a modern motorbike? Its all about the charm of the older tech doing its thing. But let's be clear: in the motorbike world no-one would consider making a flat head motor these days like what's in the Indian 741. SETs made a comeback for a reason (an engineering reason). I find it really peculiarly human that the people that are the most critical of my views of SETs seem at the same time seem the
least interested in what that reason is.
