Thanks for the reply. I'm evidently not a long-time or frequent contributor to ASR, but I've been reading this forum daily for a few months now and I understand its purpose and culture. I see a range of comments in this thread, a fraction of which I would call genuinely dismissive or hostile to the amplifier, its designer, and/or its builders. Others seem to judge the amplifier against an objective standard that the it was never intended to meet.
I'm an electrical engineer by training (though I don't work in the field) and I daresay I know as much or more about audio amplifier design than the majority of ASR members. The ACA is not something I would build for myself personally. But I know exactly what Nelson Pass' design philosophy is and what the purpose of this amplifier is. Even though I'm not interested in building the amplifier myself, I find the concept interesting and it makes be happy to see people enjoying playing with this circuit.
The hardest part of any DIY project is building the box. The official ACA enclosure is a sweet-looking thing. I would have a hard time duplicating it for under two hundred dollars. If I had one of these amps, I would use it to drive horns or desktop speakers and have fun with it on its own terms.
I have even less interest in owning a Chinese Class D desktop amp than I have in the ACA. There are people who have built and listened to the ACA who are genuinely satisfied with its sonic performance. I feel no compulsion whatsoever to comment disparagingly on their subjective experiences.
Back in the day I had a chance to listen to a Pass Aleph 3 and I was astonished by how good it sounded. Objectively good in terms of the state of mind I experienced listening to it, for whatever reason. I don't think any of Pass' commercial products are particularly good deals and some of them are way over the top, evidently designed to appeal to the sort of buyers that make ASR readers roll their eyes... to put it politely. Personally, I don't feel the slightest outrage or indignation at the existence of this three hundred dollar oddity. It is what it is. Anyone who is looking for a state-of-the-art DIY power amplifier project would do quite well to check out the Wolverine thread that's currently underway at diyaudio.com.
What I'm about to say will probably bring a lot of criticism down on my head, but ASR is not science. We do not listen with meters. Our brains do not objectively transcribe auditory stimuli into perceptual experiences. The idea that an amplifier should be a "straight wire with gain" is a defensible position to take, but it does not and cannot tell the whole story without taking into account the extraordinary perceptual processing that takes place in our brains. I find this forum useful because of the measurements, but the bulk of the discussion contributes nothing to the science behind audio engineering.
I find most subjective review magazines and websites to be nonsense. Sometimes I find myself getting bent out of shape when I see ads and reviews for snake oil products. But then I think about how much us-versus-them hatred there is in this world and I ask myself just how much I am really being harmed by snake oil audiophoolery. I am forced to conclude: not very much.
Live and let live, I say.