High Current vs high power

Agree with Al's last post. Stats, IMO, while not controlling factors, are nonetheless relevant and informative.

As I posted some time ago, I rued matching my ARC tube amp with my Paradigm Sig 8 v3 speakers. The S8s looked like the most tube unfriendly speakers one would want to match with a tube amp. And the truth be told, a Paradigm tech person strongly advised that the S8s should be driven with a high current/high power SS amp. Oooopps.

What confounded me was why my ARC VS-115 tube amp seemed to do a pretty good job driving the S8s even though on paper one might think otherwise. Well, it may still be the case that a high power/high current SS amp very well may be a better match with my S8s.

But then again, after a ba-zillion on line and off line messages with Al and Ralph I finally started to understand why my ARC amp did a good job with the S8s. There's a very important stat that I overlooked -- my amp's output impedance. Al and Ralph had to use a carbide steel drill bit before I finally got it in my head that a tube amp with "relatively" low output impedance and moderate negative feedback might perform somewhat like a Voltage Paradigm amp -- that is a SS amp.

In fact, ARC's literature reports, as confirmed by John Atkinson and Soundstage magazine, that the output voltage regulation of my old VS-115 and current Ref 150 off the 4 ohm taps is +/- .4 or .5 db regardless of speaker impedance and frequency. In addition, the damping factor of both amps, while not 1000:1, is still respectable. And that folks is why my ARC tube amps are able to do a credible job driving my "tube unfriendly" S8s.

Does that mean I should forego live auditions?? No. Does that mean stats tell me everything? No. But as Al just said above, if I have an interest in road testing a tube amp that performs like a Voltage Paradigm amp with a so called "tube unfriendly" speaker I should still give it a whirl (audition). I might be pleasantly surprised. And I have been!

So IMO a basic understanding of stats does have some benefit and informative value.

Thanks again Al and Ralph.

Bruce

P.S. I have a passing interest in checking out the Revel Studio 2 speakers. Revel's sales literature and member comments both state that the Studio 2s will sound best when driven by a high power SS amp. That sounds familiar. But I think Al might say don't automatically rule out trying the Studio 2s with my ARC tube gear. One day I just might!

Hi Al
I wrote that specs are useless because I've seen too many people refuse to even listen to some equipment based on specs alone. I'll admit when starting out I was one of them. I found that I believed specs more than my ears. Later I used my ears. I will admit the only specs that are meaningful would be input and output impedance matching of sources - pre - and amps along with capacitance and inductance of cables. But as far as power and THD a lot of those specs don't necessarily mean more power or a lower THD will sound better especially with your equipment. I'll use my Dyn - Bryston/Octave example. Dyn states my C1's need 180W or more to sound best. The Bryston B100 had 180W (test sheet showed over 200w @ 4 ohms) and the Octave V70SE has 70W at 4ohm. As good as the Bryston was it wasn't until I had an in home demo of the V70 that made me realize that V70 sounded more powerful and has more 'control' over the music.

Bryston has THD+noise:<0.005% 20 to 20khz at 100w into 8 ohms

Octave V70se THD < 0,1% @ 10 Watt into 4 Ohms

Based on those specs one would think the Bryston is a lot better for the Dyn C1's. Honestly it isn't even close. The Octave is a whole lot better which is a reason I stated specs are useless.

George

Thanks, Bruce. Yes, looking at JA's measurements of the Revel Ultima Studio 2 and your Ref150, it strikes me as a reasonable possibility that they would be a suitable pairing, using the 4 ohm tap.

George, I see your point. But I doubt that there are very many serious audiophiles who would either choose or reject an amplifier based on THD numbers, which are among the most useless audio-related specs I can think of. But even those numbers can be useful. I would be very hesitant to buy an amplifier having exceptionally LOW ("good") THD numbers, because that would probably signify heavy-handed application of feedback in the design. The probable consequences being sloppy performance on fast transients, and increased amounts of distortion components that are particularly offensive.

As far as power is concerned, yes, which of two amplifiers will "sound" more powerful has to do with dynamics, distortion characteristics, power supply quality, and other factors that don't have much correlation with the number of watts they can produce. However, to produce a given desired maximum volume level at a given listening distance, with a speaker having a given efficiency and given dispersion characteristics, requires a certain minimum number of watts. If the amplifier is substantially underpowered relative to that number, it suggests caution or rejection. If the amplifier is way over-powered relative to that number, it suggests that its gain should be looked into, because it raises the possibility that gain may be high enough to necessitate using the volume control at settings that are undesirably low.

So even those numbers can have their usefulness in some circumstances.

Regards,
-- Al

Great Thread Kelpie! Fact for any thread that garnishes response from the likes of AL, Ralph, Bruce, Zd.

It is Al's position on specs that drives my quest for understanding.

Here is a link that might help some with this equipment matching issue: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

Al is correct- THD is the sort of thing that may well have a reverse correlation with listening experience and for the reason he mentioned. I'm not a fan of *high* THD either, as the ear will convert the experience of distortion into one of tonality (odd orders contribute to brightness, the 2nd harmonic contributing to lushness). If distortion is present, detail can be obscured by the ear's masking principle.

The bottom line here is understanding how the ear perceives sound, and working with those rules rather than against them with the audio equipment design. Because designers frequently do not understand the way the ear hears things, we often wind up with spec sheets that don't seem to tell us anything about how the equipment sounds, even though that is what the spec sheet really should do.

In short, as an industry we often measure things that are not important (and place excess value on those measurements) while at the same time not measuring the things that **are** important (and placing no value on them at all...). Hence we still have to audition audio equipment.