I think I've made up my mind

Mapman, what I have posted here are specifically the impedance numbers for the REF3 and XA-60.5, including test measurements from John Atkinson for the XA-30.5, which correlates to the XA-60.5 (comparing the specs on the Pass Labs website).

Atkinson measured an output impedance spike from the REF3 at of 1437 ohms at 20Hz in balanced mode. That spec still provides at 20:1 ratio into 30K ohms.

These numbers are well within the generally accepted range for impedance matching.

Nevertheless, if you have specific numbers that would suggest a non-optimal match, then I'd be interested in seeing them and learning more.

Certainly, my experience with the REF3/XA-60.5 match was that the sonic results were not the best I had heard.

"Nevertheless, if you have specific numbers that would suggest a non-optimal match, then I'd be interested in seeing them and learning more."

No.

I'm only suggesting (as unless I'm mistaken I recall you have suggested to others as well in past threads) that if what you heard was not good, and a tube pre-amp was used, an amp with 60K, 100K, or 200K input impedance would probably sound different and might sound better than one with 30K input impedance, all other factors aside.

an amp with 60K, 100K, or 200K input impedance would probably sound different and might sound better than one with 30K input impedance, all other factors aside.
Mapman (System | Reviews | Threads | Answers)

It might. Not having heard a match with those specs, I can't say for certain.

The numbers of the REF3/XA-60.5 combination suggest there should not have been any mismatch whatsoever if one agrees with the thorough contributions of member Almarg (and others) on this topic.

Anyway, the horse is dead.

Tvad,

Understood.

My recent move from an amp with 62K input impedance (Musical Fidelity A3CR) to one with a 100K input impedance (BC ref1000mkii) produced a difference in sound of the type and magnitude that would seem to support this theory and the physics behind the theory makes sense to me.


That's not to say that such a change in a single spec assures better sound, but the effects may be somewhat predictable in the case of impedance matching when heard I believe, which is of benefit.

The change in sound in my case was a marginal but noticeable improvement in overall clarity, dynamics and detail. That is pretty much what I was looking for in going to a SS amp (class D in this case) with higher than average input impedance specs that appeared to be a safer if not necessarily better match with a tube pre-amp.

Whether the resulting sound is better or not is always a matter of taste and preference and other technical factors as well. Specs are a guideline to better sound perhaps in some cases (like impedance matching) but only tell part of the story.

I think one of Bel canto's rationals for the design of the mkii version of the Ref 1000s was to help assure an optimal match with more pre-amps, tube pre-amps in particular. The input impedance was raised from standard IcePower 10K input impedance in the original ref1000s to 100K (unbalanced)in the newer mkii versions, which is largely why I sprung for the much more expensive mkiis over the originals, to help assure optimal results with the ARC sp16 pre-amp in my system.

Since higher input impedance always appears to be better, why don't SS desingers provide 100kohm input impedances. I would think the problem is that to do so requires a tradeoff they are not willing to make, but I don't know what that might be -- anyone?