Current amp vs Voltage amp

People like Atmasphere & Berning do that. And, back in the old days there was Harvey Rosenthal (?) who came up with the 1st zOTL amp (I think I'm remembering this correctly??)

No. Harvey Rosenberg had a contract for a while with David Berning (which never went anywhere), at or near that time he coined the 'ZOTL' term, which refers to David's amplifiers (which employ an unusual output transformer, one lacking the usual limitations of normal output transformers; IOW not an OTL, and a brilliant design regardless).

The output transformer is put in place between the tube power output stage & the speaker input to buffer the tube amp from the wild swings in the impedance & phase of the speaker.
On the primary side of the output transformer, the tube power output stage sees a constant impedance. By working into a constant impedance, there is optimum power transfer from the tube output stage into the output transformer primary windings load impedance. So, the waters (if you may) are calm/serene.
On the secondary windings side of the power output transformer, the waters are rather choppy due to the speaker impedance & phase variations vs. freq. Several output taps are provided to match the speaker impedance such that there is more optimum power transfer between the secondary windings & the speaker input.

This set of comments are incorrect. The transformer does not buffer impedance or phase at all. It *transforms* it (hence the term). So whatever swings of impedance seen in the load are translated to much higher impedances which are what the tubes see. If the impedance of the load is too low, the tubes will make distortion and less power; if too high the transformer will ring (distort). That is why taps are provided.

This is also why a lot of designers see the need for negative feedback, to tame the distortion of mismatched loads on the tubes due to impedance variation in the load, as well as the distortion of the transformer itself.

You can have impedance variations in the load and have it work perfectly fine with an amplifier that has no feedback; that is to say that feedback is not required for a neutral presentation on a speaker that has a variable impedance curve. It turns out that the ear has a tipping point where it will favor tonality due to distortion over actual frequency response variation (and FWIW, just look at the charts of any speaker- **no-one** in the world has actual flat frequency response from any speaker; this is why I see the Voltage Paradigm as an entirely failed concept, not the least of which it ignores human hearing rules). IOW its often far more important to have low distortion in many cases than perfect voltage response.

As Bifwynn found out, it is the interface between the amp and speaker that is far more important than the cost of either the amp or the speaker. When you understand the Voltage and Power Paradigm concepts essentially you take a lot of the guesswork out of matching amps and speakers.

Imagine the money saved if the industry actually talked openly about this!

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.

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.

Ralph, thanks for your characteristically erudite inputs. I think I understand this, and it seems to make sense to me.

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

Why are there speakers designed with widely fluctuating impedances and steep phase angles in the first place? Why is there not more of an effort to build speakers with flatter impedance curves and gentler phase angles? Is the availablility of many high power solid state amplifiers to compensate for this their bail out safety net? Is there the belief these types of speakers sound better than those with easier load characteristics?
Regards,

Why are there speakers designed with widely fluctuating impedances and steep phase angles in the first place? Why is there not more of an effort to build speakers with flatter impedance curves and gentler phase angles?

IMO, it is because building a speaker with a flat impedance & phase curves requires some serious engineering & knowledge of physics. Not every speaker manuf has that; in fact, most do not. They cover this up with marketing hype - computer-aided design, CNC manuf, lustrous finish, exotic woods, Berrylium & Diamond drivers, blah, blah.
There are several trade-offs in manuf speakers such as on-axis & off-axis response, power handling, sensitivity, resonances, tuning the port, bass overhang, etc, etc. I am no speaker designer expert but I've spoken with a few manuf in the many years I've indulged in this hobby.
Most of these speaker manuf will make certain trade-offs that will yield wild/roller-coaster impedance & phase curves. With the wide availability of class-AB high power power amps, they figure that some amp on the market will drive their speaker. And, coupled with this is the reliance by the speaker manuf that many, many listeners will not know the difference & not know any better. A speaker that is distorting due to impedance & phase mis-management can be sold to these people as one having more "details" in the sound. Also, such speakers have a "wow" factor - hear a demo in the audio store or in-factory. The person is sold & buys the speaker. A little while later you read a "listener's fatigue" post on Audiogon from this person!
This is gradually changing & will force the speaker manuf to wise-up & not output junk designs but the process is slow.
That is why I hear: ARC used to voice their amps with Vandersteen, Avalon with Spectral & MIT cables, B&W voiced with Classe amps & so on. Deviate from this combination & you will be in sonic hell (as Bifwynne! :-)
I'm sure that there are other (better) reasons & I hope that some other more knowledgeable members chime in.

Bombaywalla,
I appreciate your perspective and input.It does seem the existence of high power SS amps can allow certain speaker faults to be some what masked by applying brute force as a remedy.
Regards,