high power tube amps vs ss

Thanks again as usual Ralph and Al. Just want to re-post 2 links that answer in part how NF may work with tube amps driving “mountainous” impedance curve speakers.

The links show bench test measurements of 2 different ARC tube amps: (a) the new REF 150 as tested by John Atkinson of Stereophile in 2012; and (b) the VS-115 as tested by Soundstage in 2008. You'll note that both techs drove the amps into simulated speaker loads. Links of the simulated loads are also copied. While the simulated loads are not identical, they are both pretty steep in the same FR areas.

What I thought interesting is that both amps had roughly similar output impedance and NF specs. Also the output FR of both amps driving the simulated loads followed a similar pattern of reducing the impedance “mountains” into “small hills.”

I realize the only way to really know what’s happening is to mic an actual speaker’s FR output. But having said that, I suspect that an otherwise flat FR speaker that was designed to be driven by a low impedance SS amp, if driven by one of the ARC amps would be in the same actual "FR" neighborhood.

Acoustic colorations? Yes, some. Wild fluctuations – doubtful, given the bench test results. Possibly +/- 1 db or less, especially if the 4 ohm taps are used.

I realize that the “cost” of using the NF is TIM and odd ordered harmonic distortion as Ralph, Al and others have explained, but isn’t that part of the amp designer’s decision trade-offs??

http://www.stereophile.com/reference/60/index.html

http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements

http://www.soundstagenetwork.com/measurements/amplifiers/arc_vs115/

http://www.soundstagemagazine.com/measurements/test_amplifiers.htm

Regardless of design paradigm, isn't it the frequency response and distortion measured in the end that matter? These are components designed with certain criteria in mind that are obviously not interchangeable and must be matched together somehow. Its important to be aware of the technical details that matter, like impedance characteristics, to have the best chance of getting best results, but in the end, I do not think either paradigm can be measured as definitively better, although I suspect that the way these things are usually determined, via certain accepted distortion measurements, etc., that the common voltage paradigm measures better when done correctly. Of course doing it correctly is a big if given the multitude of choices, in lieu of a reliable consultant or knowledge needed to make the right decisions. Power paradigm has the advantage in that the smaller minority group of vendors that follow it these days offer good consulting on how to make it work. They have to, otherwise confusion and dissatisfaction might reign, as it often does in the more "open" volatege paradigm world. Knowledge is a key ingredient for good sound, so you need it regardless and when you find a good source of knowledge that you trust, I'd say go for it in that it is likely the ticket needed for good results, if you can afford it.

THis interactive chart is a fantastic reference resource.

Not only does it help you understand how music works, but also relates that to ear sensitivity, ie frequencies that our ears are most sensitive to, at least normally.

So when looking at frequency response curves for a particular setup for example, compare what is measured to ear sensitivity as indicated. Also consider the harmonic elements that comprise various instruments in the recording as indicated in the chart. That should help one really assess what is going on when they listen better.

I have a framed copy of a poster of this chart hanging in my main listening room for easy reference when needed. The paper is not interactive though unfortunately... :^).

Great chart Mapman. The chart also provides insight into why a speaker may subjectively sound bright or flat (i.e., dull). The chart shows that our ears are very sensitive to midrange frequencies. So, if our audio rig emphasizes frequencies in the 2K to 3K range, the speaker may sound "bright." And I assume the opposite is also true.

One additional factor to consider is how individuals hear. I doubt any two people hear exactly the same plus all our hearing changes as we age. Those 50 or over may be challenged to hear test tones much above 10-12Khz or so. That can be a mixed blessing when it comes to how gear sounds in that younger ears may have greater sensitivity in that range. Age might be one of the most telling factors regarding what "sounds good" if such a study were done I believe. Also note that the chart indicates that even though we may not "hear" higher frequencies, we may still be affected by them via other senses.