Current amp vs Voltage amp

One of the reasons I chose the Daedalus speakers I have is that their combination of a pretty much flat impedance curve, high efficiency, and high power handling capability makes them suitable for use with just about any amplifier out there...

indeed good qualifications for a speaker to have. Empirically you will find that the people obsessing the least about amplifier-speaker interface are those that have understood the need for the speaker to have a relatively flat impedance & phase (let's not forget that phase response!) curves vs. frequency. Often in these speakers the curve is -3dB at 20KHz which I have been told by certain speaker manufs that this provides better in-room acoustics (vs. a speaker that has no turn-down at 20KHz). Such flat impedance speakers speak about the manuf ability to understand playback requirements & the ability to produce a product that is largely agnostic of the amplifier. Few such speaker manuf exist.....
I heard the Daedalus at RMAF one year - I remember that their sonics were very good. Best regards.

Al and Bombaywalla, it's a shame that only now am I starting to appreciate the import of impedance and phase angles plots. Had I known this before, I would have approached my speaker and amp purchases differently.

As I posted above, even the "mighty" Revel Ultima Salons have roller coaster impedance curves, albeit more tube friendly than my S8s. At least Revel had the curtesy of including in their sales literature advice that their speakers sound best when driven by a high current/high power SS amp.

At this point, I'm standing pat for now. As I mentioned, I switched over to the 4 ohm taps on my ARC VS-115 tube amp. I think the S8s sound less forward because the midrange is toned down. Although the bench test reports I posted on the ARC Ref 150 and VS-115 suggest that using the 4 ohm taps smooth out the FR variations at the amps' outputs, I'm not sure how that translates into speaker output.

My understanding is that the S8s are ruler flat when driven by a solid state amp. Perhaps, using the 4 ohm taps lowers the amp's output impedance (maybe .5+ ohms) enough to smooth out the speaker's actual FR to approach a near zero output impedance of a SS amp. Dunno.

If my wife would let me switch out gear, I'm not sure whether I would flip the speakers or the amp. The S8s are the darlings of the reviewer community, especially because of the Be tweeters and top grade engineering, R&D and QC that goes into their manufacture. The VS-115 also has garnered high grades.

If I was to flip speakers, I probably would opt for the Revel Studio 2s, but would need to also flip for a high quality tube amp, maybe the new Ayre VX-5. Dunno???

Sorry I got to this late.

It seems there are some things that need clarifying. If I am not beating a dead horse too much...

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.

With regards to Current Source, Power Source and Voltage Source:

If the amp has a lot of voltage feedback it could become a Voltage Source. Most Transistor amps attempt to be Voltage Sources (and most of them run a lot of feedback). What this means is given a sine wave input signal, and a load of variable impedance (like a typical box speaker), the output voltage will always be the same. Note that with this model (the Voltage Paradigm) the *current* will vary as the load impedance varies. This is how such an amp can double power as impedance is cut in half, as with half the impedance the current will be double.

Under the Power Paradigm the amplifier will attempt to make constant power into any load rather than constant voltage (there is a little math of note here, Power = Voltage X Current). IOW a Power Source. This is the behavior of a tube amp without voltage feedback. Depending on the load variation, both output voltage and output current will vary.

Under the Power Paradigm, the output impedance of the amplifier is in fact the actual impedance of the output section of the amp.

An amplifier can also be a Current Source, although there has never been a paradigm of design, test and measurement that has evolved around it. This type of operation is done by using current feedback rather than voltage feedback. Constant Current amps tend to have a very high output impedance by any measure, often well above 50 ohms. This does not mean that they cannot work with conventional speakers. Nelson Pass as done a lot of work in this area in recent years.

My understanding is that the S8s are ruler flat when driven by a solid state amp.

I doubt that, Bifwynne. With a SS amp, with the output impedance being very low (well into the sub-1 Ohm region), the amplifier is much less perturbed by the roller-coaster impedance & phase response of the speaker. The low output impedance of the amp allows it to sufficient source/sink current into the speaker to give you good sonics & dynamics (assumption is that the power amplifier has a robust power supply that is able to more or less double in wattage for each halving of the speaker impedance). So, the speaker will still have its roller-coaster impedance & phase responses but you will hear less of it with a SS amp.

Perhaps, using the 4 ohm taps lowers the amp's output impedance (maybe .5+ ohms) enough to smooth out the speaker's actual FR to approach a near zero output impedance of a SS amp. Dunno.

No, that's not what happens. The output impedance of a tube amp is dictated by the # of the tubes used in parallel in the output stage & the amount of global negative feedback used by the designer (each & every electronic output device - tube or transistor - inherently has local negative feedback in it. You cannot get away from this local feedback. To quote Nelson Pass in one of his White Papers "show me an electronic device & I will show you the local negative feedback").
Tubes usually have a very high output impedance relative to a speaker hence you have to jump thru some hoops to make a tube amp drive a speaker directly i.e. without output transformers. 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??)
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.
Some speakers are categorized as 8 Ohms speakers by their manuf. Then, use the 8 Ohm tap. Other are categorized at 4 Ohms speakers. Then, use the 4 Ohm tap. Still others are categorized as 6 Ohms speakers by their manuf. In this case, one needs to try both 8 & 4 Ohm taps to see which one is better. For example, the RM10 likes to use the 4 Ohm tap for a 6 Ohm speaker. The way this amp is designed it generates more power into the speaker. (I think I'm remembering this correctly??).
So, changing the output transformer tap merely provides a way to "tune" the power transfer towards more optimum between the tube power output stage & the speaker input. The amplifier output impedance does not change in the way your sentence reads.
FWIW.

The S8s are the darlings of the reviewer community, especially because of the Be tweeters and top grade engineering, R&D and QC that goes into their manufacture.

so what?? are these reviewers your friends i.e. do you trust their judgements & opinions? Do you know them personally? have you been to their house & Listened to their resp. systems? Are their music tastes aligned with yours?
If yes, to all the above questions, then, I would buy what they recommend. Otherwise, it's just a review to be taken with a grain of salt.
Who cares about the Be tweeter, the fit & finish & the QC when the speaker manuf does not possess the fundamentals of speaker design??? Get the physics right then let's talk Be tweeter, the fit & finish & the QC. Otherwise, this is all marketing hype disguised to hide fundamental flaws in the speaker performance as you have found out the hard way. Atleast, this is my take on the matter. YMMV.

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!