Of course the implementation and application is quite different.
Well, at least you understood what I was referring to.
Which is similar to what an SMPS does. With proper filtering (actually easier since you can roll-off far below audio frequencies), you should get the same noise performance. Except that a class D amplifier doesn't have PSRR of the amplifier powered by the SMPS to reject some noise.
Similar, but as you stated before,
Of course the implementation and application is quite different.
And when the implementation and application is different......?
You usually take different precautions in the design process.
It's like taking a jet engine and putting it on a horse and expecting the horse to run faster.
I'm not suggesting an unregulated power supply, just that it's usually not necessary to go overboard thanks to the PSRR of the amplifier.
True, amplifiers nowadays have great PSRR. In audio applications though (at least where I use them), its important to keep a few things in mine, one being circuit layout, and clean voltage supply. And why not? It seems like lazy engineering practice, as if to leave something half done and have an attitude of "well... it works good enough", especially when there's a possibility for poor circuit operation because of the half-assed design.
Then again you have the usability factor. If your design works good enough, and it meets specs, its what customers want, then consider it done!
Sure, less noise is better. It only makes sense though if it's actually the dominant noise source.
Depends on how sensitive to the noise the system is, where its being applied or used, and the requirements of the system. I wouldn't want to use an amplifier that has a 1.7Vp-p output and 30% of that signal is effected by noise generated equally in various places in the system. Sure the noise doesnt have a dominant source, but its still going to sound like crap.
For power amplifiers, building a linearly regulated power supply requires huge heat sinks. And power amplifiers (apart from the class D and similar types) aren't the most power efficient to begin with due to biasing.
Once again, usability. I keep bringing up this usability factor, but the truth is, it's what separates good engineers from bad engineers. Good engineers keep this in mind when they design products, they think about the system in terms of its electrical performance, but they also have to consider the user.
Sometimes sacrifices have to be made in electrical performance (efficiency and size being two examples) to accommodate the end user. Switchers definitely not the only option out there, some googling would open you up to a whole bunch of possibilities or even improvements to existing designs, try it, you'll be amazed.
blindly throwing money improving a power supply.
This is called blind engineering, or brute force engineering. It's a very unwise practice, no self respecting engineer would do this. When I design, I start with dominant noise sources around the system and work down from there until noise levels are at acceptable values.
I don't follow this half-assed "well it's good enough attitude" either, engineers that "do whatever it takes to get the job done" just aren't marketable in today's economy. Sometimes this requires a little extra time spent on a project, you'll see that it'll get you a long way in the industry.