Bifwynne, by adding negative feedback to an amplifier you do indeed move the amp towards the Voltage Paradigm. This is because as you surmised the 'output impedance' is lowered. I paraphrased the term because it is misunderstood however, and that is where the clarification comes in. Unsound, you might want to pay attention to this.Ralph, thanks for your characteristically erudite inputs. I think I understand this, and it seems to make sense to me.
Under the Voltage Paradigm, you have the term 'output impedance'. The term has a definition which is not intuitive. It refers to the amount of servo gain that the amplifier has which allows it to react to a load. It does not refer to the actual output impedance of the amp, as measured by any other field of endeavor in the world of electronics.
How can we know this? The answer is simple. If the output impedance were indeed lowered, the amp could drive a progressively lower and lower impedance. It might even make more power. But we see by adding feedback to an amplifier that the output power into lower impedances does not change.
IOW, what is happening is that the feedback gives the amp the ability to adapt to its load within certain limits by taking samples of its performance and using that as an error correction. The only way you can really get a lower output impedance is with bigger output transformers, more tubes or more transistors. The extra ability to drive a lower impedance does not come out of thin air or feedback- to do so would violate a fundamental rule of electronics known as Kirchoff's Law.
The difference between the Voltage and Power Paradigms has more to do with feedback then tubes/transistors.
At the same time, though, referring to the conventional and intuitive definition of "output impedance," isn't it true that the output impedance of a tube amp for its 4 ohm tap will be about one-half of its value for the 8 ohm tap? And if so, regardless of whether the amp uses feedback from its output or not, won't that reduced output impedance reduce the frequency response variations at the amplifier output/speaker input terminals that would result from the interaction of that output impedance with the impedance vs. frequency variations of the speaker? Albeit at the possible cost of compromising the performance of the amplifier itself, depending on how well the amp can handle the mismatch that may result. That often being a subjectively more significant consideration, as you pointed out in your second post.
Best regards,
-- Al