Tube Watts vs. Solid State Watts - Any credence?

Bombaywalla, I just caught your post re the Soundstage measurements of the SF speaker. I surmise that you would agree with the general view of many that when deciding on a tube amp's output taps to use for a particular speaker, that one should use the taps that sound best to that person's ears.

That said, if I was asked to guess what would be the best output tap selection for the SF speakers based JUST on graphs and NOT ears, I might have guessed the 4 ohm taps would be optimal. Here's why.

Btw, I assume the SFs were voiced to be driven by a SS amp. I also tracked down a J Atkinson bench test report of the Prima Luna HP amp. JA's output impedance measurements are pretty typical: 4 ohm taps (between 1.1 and 1.3 ohms); 8 ohm taps (about double the 4 ohm taps).

First off, the SFs are moderately sensitive. Soundstage reports 88.3 db. That bodes well when worrying about driving speakers with rough impedance and phase angle plots in the bass frequencies.

Second point. As JA reports, the amp's output voltage will vary with speaker load because of the amp's "high'ish" output impedance. Presumably, the amp's output voltage should vary less off the 4 ohm taps because output impedance is half that of the 8 ohm taps.

Third point. The Soundstage report shows that SF's FR drops off pretty sharply below 70 or 80 Hz. I suspect that the owner may be using a self powered subwoofer. If so, my reactions are even more on point.

Fourth point. The Soundstage report also shows that the SF's impedance ranges between 3 and 5 ohms between 50 and 100 Hz. In addition, the SFs are mildly capacitive (neg. 23 degrees or so) in that frequency range. Could be worse. Further, speaker impedance stays at 5 ohms or below up to 1000 Hz.

Conclusion. All in, my guess ... based JUST on the numbers ... is that the 4 ohm taps would yield a cleaner sound with less frequency response variation because of the amp's output impedance off the 4 ohm taps. In addition, the back impedance off the primary taps of the output trannies would probably be a better impedance match for the tubes because the amp is asked to deliver most of its power output in the 3 to 5 ohm range.

All the "techno" BS aside, I recommend that the owner of the SFs and the Prima Luna gear should use the taps that sound best to his ears.

"Currently am running eight EL34's tubes in a primaluna HP integrated amp to Sonus Faber Olympica III speakers"

This is a coincidence. The guy who bought the Krell FPB 200c from me is using Sonus Faber Cremona (the originals) an erstwhile predecessor of your Olympica 3's with likely the same Prima Luna integrated. He muttered something about 40 watts. He said there wasn't enough juice to push the sound out of his speakers. A few hours with the Krell in his setup, he calls me up and thanks me for the best thing he has ever done to his speakers as they really sang like they never did before. I believe Franco Serblin voiced the Stardivari's with older FPB Krells. I understand the new Sonus Faber's are more sensitive. I heard them with ARC Ref electronics and they left me cold compared to the older Sonus Faber sound. I guess the last Sonus Fabers I liked were the Stradivari's and the Guarneri Memento's (not heard the Evo's)

Not doubting what you hear in your system but I guess different strokes for different folks.

An interesting phenomena I noticed from decades of guitar amps is the tactile "snap" of tubes. Many geezers like me tried out various SS guitar amps over the years and regardless of design most of us return to the warm land of tubes (some cleaner playing jazz dudes still like Polytone amps, and bass players often prefer the extreme wattage of SS like my Class D Ampeg)…the seemingly ballsier "clean" tone (all about the aforementioned tube vs. SS harmonics) is where a lot of the mojo is revealed, as that means the underlying grease will rise to the surface. Modeling amps…meh…my hifi tube amp also "seems" to be ballsier at other than extreme levels, and those extreme levels are generally accompanied by inebriated dancing madness so they might not count.

All the "techno" BS aside, I recommend that the owner of the SFs and the Prima Luna gear should use the taps that sound best to his ears.
Bifwynne

I agree.
In that post, given that the OP declared the 8 ohm tap was the best for his SF speakers, I tried to see if I could co-related his decision to the impedance & phase plots I found online.
So, it was the other way around.
I thought that was clear from my post since I quoted the OP before starting my reply but I guess not. Sorry if I lead you & others into thinking that one could read graphs & make a final decision which amp tap would be the best.

I'm not even treading into the realm of "is 14dB too much global negative feedback?"!! ;-)

@Bombaywalla ... "I'm not even treading into the realm of "is 14dB too much global negative feedback?"!! ;-)" Scardy-cat! :) LOL

Re NFB: FWIW, many years ago, I recall speaking with either Lenard or Kal (ARC customer service tech rep; Len has since retired) ... I can't remember which one now ... and I asked about ARC's use of NFB in their amps. The answer was that many electrical variables are taken into consideration when designing an amp. So ... ARC's end product is the result of many engineering compromises that are made to achieve an optimal result. No perfect answers or solutions to an engineering problem that entails making trade-offs.

@Bombaywalla ... do you understand the term "[o]utput stage coupling is a combination of “ultralinear” and Audio Research’s patented “partially cathode-coupled” topology ..."?? I have a rough understanding of ultralinear .... No clue about "partially cathode-coupled” topology. Any idea??