Why Class A? Wasting power is something of the past

[BrianEno]

Nice to have a special forum for a amplifierbrand. It will create a solid base of followers.
First of all I´m not a technician or audiodesigner. Just a customer of highend audiogear for the last 20 years.
Had the privilige to own several poweramplifier designs from Colangelo (ML-3), Agostino (KSA-100, KMA-200´s), Jeff Rowland (model 7 Series II, IV and model 8T) and Nelson Pass (S/300 and S/1000´s).
In the eighties Class A was the buzzword in highend and hifi world. John Curl designed for Levinson the ML-2 a 25 watt amp which consumed 400 watts at all times. Saw a lot of ML2´s with there heatsinks in time turned purple or even gold because of the heat. Krell was king in that area though. They specialized in copiing the designs of Levinson but make it even more outrageous with a designs like the KRS200 and six piece KRS-1. The more "modest" designs like the KMA-200´s drew a constant 1150 Watts from the outlet to retain the magical 200 watt Class A. It needed two noisy fans to cool it down. Threshold started with a original concept to tackle the constant draw of current with the dynamically biased 800A which at idling only consumed about 200 watts. In 1980 came the Stasis 1 (still the most sought after amplifier from Pass, also for it´s gorgeous looks, never superseded again in my opinion, probably thanks to Rene Besnee) with a completely new operating concept. From the accompanying brochure at that time: "Threshold Stasis amplifiers move beyond "class" designations through achievement of a completely new operating concept." In the accompanying tecnical paper (extremely readable though) a few years later with the introduction of the S/150 - 1000 series Nelson Pass stated that "While Class A operation was capable of reducing this effect (current variations in the gain devices) by swamping it with a large idle current, a method of reducing the current fluctuations would tackle the problem more directly. If one could envision a tandem arrangement of gain devices where current fluctuations were surpressed instead of voltage fluctuations as in cascode operation, this effect would be achived. Out of this concept came the STASIS amplifier.
So obviously there was no need anymore for that thermally stressing, power consuming ecologically unfriendly and in the summer to hot Class A biasing. Problem solved case closed! But then came the SA series after that the Aleph and now the XA series with a behemoth XA-200 of 80 kilograms idling just under the Krell and not even behaving as a voltage source because 200 Watts is the maximum you can get out of it according to the designer. The meter won´t move either than I suppose it just shows you the constant currentdraw from your pocket.
Krell (after abandoning the forced cooling and ridiculous large protruding sharp coolingfins (KSA-200 for example) and Levinson (always the more refined anyway of the two) got sensible and are now deploying plateaubiasing. Jeff Rowland has taken the real bold move to dispense with heat alltogether with his Icepower designs wich is the way of the future. He should only remove the heatsinks from his 300 series because there´s no need for it anymore just like the meter on the XA series.
So why is perspective with the other manufacturers of highend audio/amplifications has Nelson Pass revert back to energy wasting solutions from the past. Why is he back to square one in that parameter?

PS Found a series of photographs from the seventies of Threshold in www.passlabs.com/threshold One portrayed a Mark who later became president of MLAS. Is this Mark Levinson or Mark Glazier or just a stupid question.

[Babowana]

Maybe Papa doesn't know how to make good AB . . . ?

[badman]

What's your motivation here? It sounds as if you're looking to bash a skilled designer for his design decisions. The advantages/disadvantages of Class A have been discussed to death in various forums, perhaps a few searches are in order before you call energy efficiency progress with no consideration of any other issues.

[gl]

Sigh.

[Netlist]

Bad badman.

I really think Brian's question has merit and not only from an energy efficiency point of view.

/Hugo

[Jeb-D.]

It does seem wastefull and excellent results can be had with other approches. However, by opperation no class is as pure as class A. The signal is never cut in half like in a AB or B amplifier nor is it ever hacked up then re-assembled like in a class D. As I said you can make an excellent AB,B,D,G ect. Amp, But for some people absolute pure, un-defiled audio is all that matters.

[BrianEno]

Originally posted by badman


What's your motivation here? It sounds as if you're looking to bash a skilled designer for his design decisions.

Certainly not! Have fond memories of the Threshold S/300 and S/1000 mono's in my system one of the most musical products I encountered. Love the NFB designs from Nelson Pass and Jeff Rowland. I'm seriously interested why the designer which skills I cannot and will not dispute has chosen for designs that waste so much power. That is a valid and legitimite question I backed up with the context I provided. Jeff Rowland stated it very elegant in one of his discussions he published named "A technical discussion With Jeff Rowland" subtitle: The Myth of "Class A" Operation"
last paragraph: "Most modern power amplifiers are quite inefficient and forwardthinking audio designers must become more ecological responsible by designing equipment which consumes less yet giver more." That's an opinion too made in the beginning of the nineties. Nelson Pass himself mentioned in his literature Stasis as the solution of all Class wars. He spoke over achieving linearity (his central topic in all of his discussions en designs) by swamping the circuit with biascurrent and propagated his Stasis solution as a less cruder and efficient way. I think it is in no way offensive to question/ask why a designer chooses to develop designs which waste so much power while he claimed in the eighties the end of the Class wars with his Stasis concept. You as a citizen of a country that in his First Amendment guarentees the freedom of speech shouldn't curtail me by saying I'm bashing a designer. Let's have a open discussion, I'm curious aren't you? Or is he a God...

[jacco vermeulen]

The pic is Mark L, NP posted it when we had a talk overhere on Mr Levinson.
Small world, isn't it.

I've heard Mr Rowland's new age power amps.
Great design, but look and sound like refrigerators imo.
The pool in the backyard wastes a whole lot more, i kinda fancied nukes in a weird way too though.

[el`Ol]

I heard several powerful amps at the Highend in Munich this year and the (class A) Electrocompaniet Nemo had so much more soul than what I heard from Mark Levinson, Jeff Roland and (worst of all) MBL. I have my doubts this will ever change.

[Netlist]

You will want to read this old post from Nelson on the subject:
http://www.diyaudio.com/forums/showt...173#post558173

While it is true that the best power is the not-consumed one in terms of efficiency, I replaced a bunch of old light bulbs in the house with low-power ones. It turns out that I can enjoy many more hours of ClassA sound with an equal yearly electricity bill.

/Hugo