Mapman; No I haven't heard any class D amps with my Martin Logans. I would be very interested in hearing some. If Jeff Rowland amps are Class D, then I know he did it right. Switching power supplies are not new. They were/are used in auto amps because the voltage was 12VDC and to get the power needed without large current, you had to increase the voltage. P=IV=VxV/R=IxIxR. So, if for a auto amp you wanted 100 Watts, then 100=IxV and therefore, I=100/12 = 8.33 amps. Thats it! So to get stupidly high power out of auto amps, you need to step up the voltage to keep the current low and still produce high power. this eliminated large heavy transformers and storage capacitors. But, the drawback was that the switching power supplies generated a lot of noise that had to be filtered and this was really difficult to do. For home amps, the process is the same. They probably use switching power supplies with lots of large power transistors to eliminate the need for very heavy and expensive transformers. Otherwise, I can't see a reason to do this. You only need large heat sinks if you are operating in real class A. I.e. output devices biased on all the time at rated output power. That takes lots of amps and makes heat that must be dissipated. So, Class D, is to get the voltage up to a high level so that the current will be lower and to eliminate the large expensive transformers and storage capacitors. This is off the top of my head. As long as the power ratings at load along the frequency range is as advertised, I really see no difference. power is power. Either by high voltage and low current or low voltage and high current. But to drive say, 8 ohm speakers, then you need current for power. remember P = IxIxR. or lots of voltage gain for the outputs instead. P= VxV/R.
