The Nelson Pass Aleph 2 amplifier is a room heater (class-A dissipation is 300W). It produces an output of 100W into 8 ohms. Its distortion is fairly high compared to modern amplifiers.
Actually you are incorrect.
I know what it is, I have built TONS of nelson's designs.
I can't comment on the distortion because I haven't seen the whole schematic or done any tests/simulations, but he's almost right about the power dissipation. Note I said almost right, because an efficiency of 30% is optimistic. The theoretical maximum efficiency for a class A design, without a transformer, is 25%. In reality, it will be much lower than, probably around 2% under typical operating conditions.
No doubt there are plenty of cheaper, modern class AB and even class D amplifier designs, capable of the same output power level, using a fraction of the input power of this design, with similar or better distortion and noise figures.
Power dispation is correct. BUT people don't buy a Class A amplifier for it's effeciancy. They buy / BUILD them becuse they sound good
I've tried Class d and many high end brands IMO they all sound like CRap! IMO They should be used for one thing, and one thing only. Subwoofers thats it.
Or people might buy/build them because they believe they sound better. It highly subjective and could even be the placebo effect, if the amplifiers are good enough and are operated well within their power ratings. See the study linked below, which tested whether audiophiles could tell the difference between three different amplifiers: one very old solid state design, a new (back then) solid state design and a valve/tube design. The volume was set the same, taking care not to overload the amplifiers. The same speakers were used and someone, in another room, switched between different amplifiers, randomly. The end result was no one could tell the difference, any better than chance, meaning all of the amplifiers sounded the same!
http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistors%20DCD.pdfThe senses can easily be tricked. Aesthetics, brand and marketing are very influential. It's almost certain that, if I put the same amplifier circuit inside two enclosures, one which looks nice and high quality and another which looks cheap and nasty and asked people to rate how they sound, they'd pick the nicer looking amplifier, as the one which sounded better. Similar experiments have been conducted with the same food on different plates and in different packaging, with similar results: nicer packaging and crockery make it taste better!
Of course in real life, people do drive their amplifiers into clipping (overload) and that's where the differences start to appear: an old valve design might distort subtly, in a pleasing manner, whilst a modern transistor amplifier will harshly clip the signal, resulting in nasty distortion. This is why many musicians prefer old valve/tube amplifiers and your class A amplifier might sound similar.
It's true that class D amplifiers weren't very good when they were originally introduced, but some modern ICs have imperceptibly low levels of distortion, when operated within their ratings. Of course, lower distortion doesn't mean it will sound better to everyone. As I mentioned before, it's highly subjective. Some people like certain types of distortion.
If you want low distortion, your best bet is to over-rate the amplifier so it's never driven into clipping. The main source of distortion then becomes the speakers and room acoustics, which are far more important, than the amplifier design.