There is no such thing as "completely load insensitive"...
Also, it takes wrapping feedback around the output filter to REDUCE load dependence, and in our experience, this affects the sonic quality of the amp in a negative way --- no pun intended. In fact that "too much negative feedback" sound (sometimes associated with Class-AB amps) is just what you get with all the phase margin compensation that's required to do so. As long as you're not driving a ridiculously low impedance, a low feedback design sounds so much cleaner than one designed to do better on the bench than into your ears. We can all agree that bench measurements don't tell the whole story. Without writing a book on this topic here, lets just say that we started with a design that was excellent on the bench, then tweaked it over several YEARS to get it to sound the way it does.
I have been designing Class-D amps (and listening to them) for more than 20 years, and these opinions are not based on some fly-by-night theories. There are many misconceptions regarding Class-D technology, and companies that take the risk of designing their own Class-D amps from scratch can easily fall short from inexperience. Same goes for pre-fab module makers. I have seen audio companies employ switching power supply designers that have never designed an amplifier in their life to build their "proprietary amp technology". It is also important to know analog amplifier design in order to make a good "digital" amp. Yes, I know there will be somebody out there to once again point out that Class-D doesn't mean the same thing as digital, blah, blah, blah. I designed my first analog audio amp when I was in grade school, by the way... Designing analog amps is a good way to learn what results in good sonic performance versus good bench measurements. It can be considered a good lead up to digital amp design --- a prerequisite.
-Tommy
Friday, July 23, 2010
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