Ralph, You have stated a couple or more times now on Audiogon that you can measure parts....here is your latest: "Actually, a lot of the things in the list above do have measurable effects. The trick is knowing what to measure." You have never given us an example of measuring something and changing to another part and finding a measurement difference and then that difference results in a change in sound. As far as I know.....there is no way to measure resistors, capacitors, diodes, solder, wire, jacks, damping, directionality of wire, etc. If you use a large inductive part in a sensitive place...like a feedback loop.....then of course, it would change the distortion measurement.....Who the heck would use a large inductive part there? No one.
Seriously? If you want to know the effect of a part in an amp, measure the amp not the part. In a class D tiny things can have a big effect, like how a lead is terminated inside a capacitor. If the amp is noisier it can radiate noise through the air and thru the AC wiring (as well as audio grounds). When this happens, it can interfere with other equipment producing things like hum or buzz, or increased errors in digital gear.
If the circuit is also zero feedback, just about anything can affect how it sounds. Combined with degraded noise floor its hard to imagine how that will turn out well. That is why I recommend that any modified class D amp be tested to meet or exceed EU directives for radiation. Its common sense.
In case its not really obvious, getting class D amps to behave and not make noise is most of the design work. Even if your layout is good, changing a single component such as a bypass capacitor can blow that out of the water.
Sound by itself isn’t enough- if the amp is noisy its a liability. I mentioned earlier that GaNFETs can switch really really fast. The deadtime in any GaNFET amp isn’t there for the output devices - it actually has a different purpose in GaNFET amps (extra credit: what is that purpose? If you can’t answer that question you are not qualified to work on the amp). If you make a change and the amp starts switching at 40MHz for no good reason, its a simple fact that the output devices will run hotter. Heat and cooling cycles impose limits on all electronics- GaNFETs are no exception. If they fail early on because they are running hotter, that’s not a good thing, right?
The bottom line for anyone looking inside a class D amp is if you plan to modify it for any reason, there is no integrity in doing that if you can’t be sure the noise isn’t affected.