As it happens, Class A has been on my shopping list lately. So my answers are ’no’ to all three questions. But energy consumption issues do factor in.
As others have mentioned, various manufacturers use plateau bias to reduce typical class A power consumption, including Krell obviously (they’ve done that for a while). An Evolution 302 is probably the sweet spot for me (might stretch to the 400 mono pair, you never know). But it will have to be e-series, with the 2 watt standby, not the previous model, which uses ~60 watts just sitting idle. A pity, because there’s a very tidy and wicked looking black 302 (non-e) listed on the ’Gon right now.
The new one should use less energy that my current KAV-series Krell, which is AB but doesn’t have an efficient idle/standby. I'd be curious to see how a Purifi-based amp like the tidy units Mr March makes (I'm in Australia) would sound. But I'd need to hear one, last time I tried a modern design (LLC power supply, negative feedback) the sonics were disappointing.
We pay over the base market offer for 100% green power, but still factor energy efficiency into purchasing decisions. For most anything that uses significant power. There’s no need to be a f*ckwit.
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Sorr @axo1989 New Krells are NOT pure Class A. So called anticipator circuits don't work So called plateau bias doesn't work. No short cut to good sound. No free lunch.
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@clearthinker
Sorr @axo1989 New Krells are NOT pure Class A. So called anticipator circuits don’t work So called plateau bias doesn’t work. No short cut to good sound. No free lunch.
I didn’t mention new Krell, Evolution series are D’Agostino designs (even though the e-series appeared after he and Rondi were forced out). And sustained plateau bias (and active cascoding) works—obviously—in the sense that it does what it’s designed to do, prevent notch distortion (the basic reason we want Class A) while reducing power consumption.
But if you want to argue that isn’t pure Class A, fair enough. I can change my answers to no, no and yes, respectively. Unless I change to high efficiency speakers and a low powered amp (and accept the tedium of constantly switching the damn thing off and on again) I’d steer clear of old-school Class A.
But while you're there, and since you are obviously into it, do you think the really old Krells sound better than the ones I have in mind?
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PS: I did look longingly at the KAS pair that a guy in Melbourne advertises from time to time. Beautiful. Logistics though. Re your amps, KRS 200 was the original Class A version and the S was their sustained plateau bias model, yes?
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Really, this is a thing? I've been running Class A for years and it really hasn't had any noticeable impact on my home energy consumption over other amp classes or tubes. I'm currently run a Pioneer M22 which is 30wpc pure Class A and it would take a heck of a lot for me to move away from it. Each to their own though.
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Pass Aleph 1.2 Pure Class A 150wpc monos and will never get rid of them.
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@yyzsantabarbara No I haven't. I am not looking much for upgrades any more and I don't go out listening to new kit. After nearly 60 years, I'm in the lucky position that I love my system the way it is. I occasionally buy a phono cart, mainly top-end Ortofon. I changed my pre-amps 4 years ago from old Audio Research to vdH The Grail and Audio Research Ref 6. Otherwise it's all old stuff.
I read Krell Solo 575 Mono Power Amplifier 575 Watt Amplifier features 'iBias'. This is said 'to deliver the rich musicality of Class A amplifiers, the uncompromised dynamics of classic Krell amplifiers, and the efficiency and low power consumption of Class G and H amplifiers.' Sorry. I don't believe you can get something for nothing. In their publicity Krell extol the virtues of Class A and pretend they are still building it. Neither do I trust Krell since the D'Agostinos were fired. The way that was done suggests the new owners are bad guys not to be trusted.
In 2015 they cost $22,500/pair. Not a lot, in the context. Fremer's 2015 review was 'equivocal', although Atkinson found it measured 'impressively'. For those that are concerned, the power supply isn't stiff; output doesn't double up down to 4 ohms, let alone 2.
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The minimal amount of heat from a class A amp is equal to 4 x 100 watt light bulbs approx. no big deal and since I love the sound I see no reason to ditch the amp becauseof heat, unless one wants a new toy for the sake of a new toy.
The cost of elctricity in my area is 12.5 c per kw hour. Multiply by .4 kw and my amp costs 5c per hour to run. I am more than happy to put another nickel in the slot every hour :)
Maybe class A amps will become more popular when homes are mandated to have non fossil fuel or natural gas heating.
Compared to a 36.2 kw electric furnace .4 kw ain't nuthin.
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@avanti1960 Wrote:
The minimal amount of heat from a class A amp is equal to 4 x 100 watt light bulbs approx. no big deal and since I love the sound I see no reason to ditch the amp becauseof heat, unless one wants a new toy for the sake of a new toy.
The cost of elctricity in my area is 12.5 c per kw hour. Multiply by .4 kw and my amp costs 5c per hour to run. I am more than happy to put another nickel in the slot every hour :)
I agree! 😎
Mike
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in the sense that it does what it’s designed to do, prevent notch distortion (the basic reason we want Class A) while reducing power consumption.
@axo1989
Just so you know, any class D amp that uses a choke-filtered output (which is nearly all of them) are incapable of notch or crossover distortion.
I read Krell Solo 575 Mono Power Amplifier 575 Watt Amplifier features 'iBias'. This is said 'to deliver the rich musicality of Class A amplifiers, the uncompromised dynamics of classic Krell amplifiers, and the efficiency and low power consumption of Class G and H amplifiers.' Sorry. I don't believe you can get something for nothing. In their publicity Krell extol the virtues of Class A and pretend they are still building it.
@clearthinker
Krell has used a sliding class A bias system for years. The way it works is at lower signal levels the bias is also reduced. As the amplifier power increases, the bias linearly increases with it. In this way it can be biased in the A region all the time (in this case meaning both output transistor banks are active throughout the entire signal waveform) at any power level the amp makes. Because music tends to have lots of transients that are short duration, even though the amp might be quite powerful the net result is it will run cooler and draw less power, significantly so.
If you were to run it at full power long enough for it to heat up, you would find it making the same heat and drawing the same power as any class A amp capable of the same power.
My point here is that its not a 'get something for nothing' proposition as you suggest. Seems to me there was a patent issued on this technology back in the 1990s.
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The heat generated from a class A tube amp is significant and can be annoying. I have a Black Ice Audio Fusion and a Cary tube amp. I can only run them in the cooler late autumn through the winter seasons. The rest of the year I run bridged Schiit Aegirs and Outlaw Audio 2200 monoblocks. For class A, the electrical cost is not the issue; it's the heat. If the bias current is not spot on, the amps will overheat and shut down. The Black Ice uses four 6550s and the Cary uses eight KT88s. Yes the 6550s are the functional equivalent of oven coils although KT88s are slightly cooler. This may be sacrilege, but if I had to do it all over again, I would go with class D. My Ampeg SVT tube amp runs nowhere as hot as these stereo amps.
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@atmasphere thanks, that post was informative (both class D and Krell bias discussion). As I mentioned, I’d like to hear a Purifi class D design (either 1ET400 or 1ET7040 based).
I’m still happy to buy a Krell Evolution e-series though, I see it as the most technically advanced implementation of that design lineage. I can live with 2 watt standby. A (hypothetical) pair of 400 watt monos running 24/7 in old-school class A (no sliding bias) would be a madness though, as a main system left on all the time, consuming its rated power (multiplied by the efficiency factor) but achieving nothing when idle. That would be nothing for something.
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@atmasphere
You've been taken in like all the other punters.
The Krell sliding bias system and its predecessors are cons.
The orchestra is noodling and so is the bias on the Krell.
Suddenly the guy at the back whacks the six foot drum for all he's worth.
The guy in the amp says 'OMIGOD the guy in the orchestra has whacked that drum. For *****sake get that bias up immediately.' The other guy in the amp on the bias hears the msg and turns up the wick. But the guy in the orchestra on the big drum has already gone home.
YOU CANNOT UP THE BIAS QUICK ENOUGH TO CATCH THE MOMENT.
I have read the patent and it does not answer this. It cannot. I asked a senior engineer working on my KRS200s how it solves this issue and he could not answer.
This started as a con and remains a con. The bias cannot be changed quickly enough. The only way to do it would be to buffer the signal for a second or so which would introduce insoluable clock problems.
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YOU CANNOT UP THE BIAS QUICK ENOUGH TO CATCH THE MOMENT.
I have read the patent and it does not answer this. It cannot. I asked a senior engineer working on my KRS200s how it solves this issue and he could not answer.
@clearthink You can easily change the bias no worries.
I don’t think they want to publish the trade secret which is why its not in the patent. You are correct that you do have to be careful that the timing of everything works out. That means that you have to have the same bandwidth in both the actual audio circuit and the circuit driving the bias so that they are in fact properly time aligned (IOW no phase shift between the two at any audio frequency). You can’t have any timing constants to filter noise! It simply has to be as reactive as the audio circuit itself.
I think Krell did that- its not hype at all. The problem is that this type of circuit by definition has to introduce distortion of its own. That, ultimately, is why we never implemented it in our amps.
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In answer to the OP, I’ve got a pair of Pass XA60.8s, and living in MN, I appreciate that they are space heaters in the winter. Warm and cozy. In the summer, the extra heat is tedious and the a/c has to work harder to compensate.
I’d love to have the same sound without the heat; emphasis on same sound (or better). I’m watching the Atmasphere class D monoblocks carefully. I’d love to demo a pair, but our local dealer is a bit of a train-wreck. Still on the fence.
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I’ve only had two class A amp, and one was just "strongly biased into class A"
One was a Musical Fidelity A100X integrated. That one I kept only two weeks: it was getting so damn hot after about 30 minutes of use that I was being paranoid all the time. Even the volume control was too hot to touch. You could have grilled a ribeye on top of it. Ridiculous. I had flatmates at the time, and the stupid girl once put her syllabi on top of it, while it was on. I saw that and started to have nightmares about the house burning down.
A couple years later I bought a Sony TA-N86B. That one was amazing and never got too hot to touch even when run in full class A mode. But it did put itself in protection mode every time the room temperature would get to a certain level in summer (and I don’t live in a tropical area!) until the amp’s PSU finally died of probably unrelated causes.
Then I discovered flea power, class D chip amps (that TA2024 from Tripath!) that sounded really lovely (with a little care) on my horns and I definitely gave up on everything else.
Now I have a multi-amped system and exclusively use tiny class D amps. The system sounds great, it stays on 24/7, doesn’t produce any heat, barely uses any electricity, and never sends nasty unwanted continuous current spikes in the fragile and unprotected drivers. They also only use as much floor print as two cigarette packs each.
In Belgium where I live, the energy crisis is an abomination. I have friends earning 2000euro per months, with a 900 euro rent, who now have to pay 500 euro in monthly energy bills. It’s a nightmare. I’m so happy I’ve got my class D amps!
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I own a Pass Aleph 5 and, yes, it runs hot, but I don’t care. It sounds beautiful and that’s why I have it.
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Your paying the electric bill, so run a Class A amp as long as you want. Leave it on 24/7, it's perfectly fine. If they are so worried about climate change why were we forced to use old technology like the combustion engine for over a 100 years.
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I don’t own a class A tube amp but would love adopt one if anyone wants drop one off at my doorstep like an abandoned dog or something. I wouldn’t buy an amp because it ran cool or was ultra efficient. My decision would be strictly based on sound and how well it behaves in my set up. I can offset the Carbon Foot Print with my electric lawnmower, weed wacker and leaf blower. All of which I purchased based on performance not how green they were.
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If they are so worried about climate change why were we forced to use old technology like the combustion engine for over a 100 years.
@phd For the answer to that, read Internal Combustion, by Edwin Black.
Its fascinating reading!
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atmasphere, definately I will look in to that . Thanks
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I made a conscious decision to buy a Pass INT-25 a couple of years ago. 25 watts class A. Sounds good. I like it. I'll keep it. LED bulbs throughout my home however.
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Re: energy consumption
Bitcoin mining uses as much energy as the country of Argentina.
And that’s just Bitcoin. Adding up all the other crypto-currencies results in massive energy consumption. Does running a Class A amp matter in comparison?
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@bulldogger Thank you for telling me. But the day is over. Krell had stopped building pure Class A even before the D'Agostinos were so rudely kicked out of their own company.
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