Class A amps

My vote, A/AB is a Mule! Ha! Joking aside one of my college lab projects ended up as an audio amplifier based on implementation on Matti Otala’s ideas regarding high slew rate devices. The University I was at had access to state of the art semi-conductors as they were rolling out or in development. It was a fun time and a fun project. My project focus was on the circuit utilizing newest semi-conductors, not semi-conductor development per se. To my mind A/AB is Class AB biased high into class A for a set current. A hybrid so to speak. What one calls it is one thing, how it sounds is altogether a horse of a different color.


One amazing mule it is for sure :grin:

True but as I said in my first post, what matters is the wattage they are spec’d over. For example, Luxman specs the L590axii 30w at 8 ohm, 60w at 4 ohm, full class A.

Above that, sure A/B. That kinda goes without saying.

But Luxman doesn’t spec it above the 30w at 8 ohm, even though testing measures it up to 90 w at 8 ohm before hitting undue distortion (presumably into A/B to get there). But over entire spec range class A, so class A amp. What matters is the amplification class the amp operates in over the entire range the manufacturer specs it for.

Here’s Paul’s take on class a and class ab… simplistic but to the point…

“A few Class A watts seem to go a very long way!” I’ll say! My monoblocks are about 3 watts each and I don’t run them into clipping and they are the best sounding amps I’ve ever heard and ended my amp hunt.


So zooming in. Tell me what this means on the xa100.5 line. Does this amp push 200 watts class A or is it 100 w class A?

It is 100 WPC RMS Class A.

Hi Tim,

Sorry I can’t offer you any comparisons as I’ve only ever owned one pair of high-end mono block amps in my life! They are Electrocompaniet (EC) Nemo mono blocks. EC is a Norwegian company and I don’t know if the brand is typically available in the US.

The Nemo (AW600) is a ‘monaural class A reference amplifier’ and is part of EC’s ‘Classic Line’ of equipment, according to their website. I checked the specs and they only mention ‘600W into 8ohm’ (1200W into 4ohm). There’s no mention of any A/B operation so, unless they’re being deceptive by omission, I can only assume that it operates as ‘pure’ class A.

However, I think that’s largely irrelevant. What I can say is that it does run hot! (The specs quote 230W power consumption while idle. My (dedicated) P10 shows it at more like 150W. The power consumption does not appear to change with increased volume, well, at least at the levels to which I listen. :yum:

I can also only sing their praises. I’ve owned them for about 20 years and have yet to be disappointed by how good they sound. They still impress and despite the vast improvements to the source (currently DS DAC with Sunlight), they still improve!

I’m the first to admit how little I know about this stuff but, when I bought these, I knew even less and relied heavily on the dealer’s advice. At the time they were big on amp/speaker synergy and I went with one of their recommendations that sounded the best to me. They paired up the Nemos with B&W 801s. (I’ve since upgraded to 800s but the magic remains.)

Anyway, if you have the opportunity, I’d recommend you give the Nemos a listen.


I would be quite surprised at any amplifier than can do 600 watts Class A. Mine is rated 150 into 8 and it weighs 185 pounds and is quite large. Something that does four times that would be VW Beetle sized I would guess.

I would be very interested in knowing the detailed specifications of that amp. If it does even half that it could be enough for an arena show. :grinning:

So the story goes (can’t remember the source so can’t confirm the veracity), B&W, when they developed their Nautilus 801 speaker, they couldn’t find a suitable amp to drive them. So they commissioned Electrocompaniet to come up with something. EC ended up combining a pair of their AW180s (in series) and called it the ‘Nemo’ (get it? Nemo drives the Nautilus?)

Probably urban myth. :blush:

BTW, the 801s used to be used in the Abbey Road studios. I don’t think they use them anymore.

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Not according to the stereophile review - it seems to confirm the urban legend. But oddly enough can’t get any spec on its class A bias.

Btw. I went to Abby road. Talk about getting chills. I almost cried thinking of the history there.


Quote from hi-fi advice on aw180 and aw600…:thinking:

With “Class A” written on the front panels, one might be led to assume that these amplifiers actually work in Class A rather than Class A/B. However, these amplifiers are really cool to the touch which doesn’t rhyme with typical Class A behavior. The manuals do not specifically state the working principle so, in order to get clarity, I emailed Electrocompaniet and my mail was promptly responded to by Volker Hunger. As it turns out, Electrocompaniet uses the Class A label similar to how Technics used the Class AA label on their amplifiers in the ’80s. As Volker explained:

“All our amplifiers are Class A/B and have been for approximately 40 years. “Class A”, in this case, is rather meant as a quality designation, like reference… , first-class… High quality… We know, this term can be confusing if someone does not know about the technical details but it has been on our front plates for a long time, so this designation has been kept for historical reasons, just like the acrylic material for our front plates and the golden knobs. All pre- amplifiers and output circuits, for example in CD-players, Steamers, and the like, are a completely class A design. It’s one part of our design philosophy that transistors in these circuits “work on high class A operating points. It is also correct for all circuits of our power amplifiers in up to the output circuit. These are all Class A designs, but of course not the output section”.

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Well there you go! Thanks for the research and clarification Mark. Interesting that they report them running ‘cool’. Mine certainly run on the warm side and, as I wrote, don’t seem to vary their power consumption too much, whether idle or playing. Maybe I just don’t realise just how hot ‘real’ class A runs.

At any rate, no biggie, it doesn’t change how good they sound to my ears. :relaxed:

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I’m sure there’s something to the fact that “nemo” means “nobody” in Latin but just give me a minute…

And that’s what really counts…:grin:

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