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Re: We know the answer, he agrees with the thesis' basic premise

As soon as you go mess things up by jumping from what “a tube” does to what an amplifier (and all its parts) does, you have a different ball of wax.
For one thing, if you take a cold hard look at signal transformers, you find a multitude of flaws, one has to use them very sparingly or as Tom Dawson has, eliminate them. Curiously, some of the SET designers seem to relish using them in every stage.

Meanwhile, a “small little red flag” sticks out of nearly all of the super solid state amps.
The premise: adding negative feedback, among other things, reduces the output impedance so you get the really low damping factor the magazines suggest you need (anything over about 50 is beyond making a meaningful difference).

If the output were truly a low resistance then, when driven with an in band square wave, placing a capacitor across the output will show the rounding off of a first order RC low pass filter.

Instead, in most amplifiers, placing a cap across the output produces ringing to varying degrees and never look like an RC filter.
Ringing is a result of “higher order” stuff going on, clearly when driving a reactive load, it is NOT simply a faithful low resistance voltage source as imagined.

One real problem designing passive crossover filters is dealing with the fact that the load (the driver it’s connected to) is NOT a simple resistance where you can simply look up values. Likewise, it is customary to measure amplifiers driving a resistor, it is the combination of Capacitance, inductance and resistance it will be driving.
Many SS amplifiers reach rated power into a resistance but go into safe area protection as soon as significant reactance is connected at a much lower level.
I guess what I’m saying is that there are so many problems one can have that it is hard to list them all. Are there faithful SS amps? Yes, I think so, are there colored “euphonic” tube amps, sure but there are faithful tube amps too.

Tom Danley

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