Kijanki: Sometimes I write in the manner I speak rather than write in a more coherent manner. As an Electrical Engineer, I know the difference between Watts and Kilowatts. I apologize for not being more clear. Frankly, I wish the station broadcast in the MegaWatt range, at least the signal would be a lot stronger here. My favorite Jazz station is privately funded - their broadcast is so limited I can only listen to it clearly in Silicon Valley. East of the hills in the East Bay, their signal is very limited. Sigh...
High Frequency noise is "easy" to filter out within a band of frequencies. However, as the bandwidth increases, filters become more difficult to design and thus noise become more difficult to eliminate. When you consider you also have to filter electromagnetic noise as well as electrostatic and conducted, and the fact our noise spectrum now extends into the GHz range, it is no longer a trivial task.
Do understand that any noise spikes created by the diodes in a linear power supply is insignificant in comparison to the noise created by diodes and components in a switching power supply or class D design. This doesn't mean anything with a switching power supply is bad, but it does mean more engineering work has to be done to eliminate the resultant noise that comes along with it. Also note that this diode "switching noise" in a linear amplifier is actually the transformer radiating, not the diode. But, again, this noise is insignificant in comparison to the noise created by a switching power supply of comparable quality.
Class D amps grossly violate the KISS principal, but it is being widely embraced because most of us who have a multichannel 300W+ per channel Class D amps couldn't afford it if it was Class AB and certainly couldn't afford to operate it, much less buy it, if it was pure Class A. This is in addition to the fact that Class D makes higher power, battery operated personal stereos possible.
Given a fixed amount of money to spend, choosing a Class D amp for the midrange and upper frequencies would be my last choice over a good tube or Class AB solid state design. I do believe it is much more difficult to design an equivalent sounding Class D amp to a Class AB design.
Tgrisham: I agree with you on implementation. This Marantz amp I have had a sticker price in the 2000+ dollar range. I don't remember exactly, I would have to look at the receipt if I still have it, I am thinking it was around 2400. I bought it at 60% off due to store closure and the fact it was only four channels and not six made it hard to sell. Clearly, it isn't a cheap design - even though it is Class D it still weighs over 60 pounds. It is possible that I have a bad amplifier but I am more inclined to believe I have an implementation problem of some sort here at the house. A Class D amplifier design engineer I know now works at National Semiconductor, I think I will look him up tomorrow and discuss this noise problem with him.
Bill: I agree, the use of an amplifier as a subwoofer only makes the choice of amps much more easy. For one thing, it has only a very limited range of frequencies to reproduce and any nonlinearites created by producing 80% of the power in music is not fed to the upper octaves where your ear is most sensitive.
In addition, designing a subwoofer only amplifier is easier in that more feedback can be used without the resultant hardness through the midrange. The additional feedback increases the damping factor which usually improves the bass and the limited frequency range of the bass frequencies means upper bandwidth can be sacrificed for the increase in feedback to maintain stability.
Unfortunately, history has shown it is more difficult to sell a standalone, subwoofer only amplifier. Although once installed in the subwoofer cabinet, they seem to be selling quite well!
