Class-D or switching amps, any opinions on??

Timrhu - when you move up in power the bandwidth gets lower. Your PS Audio amp's module has higher (65kHz) bandwidth than more powerful 1000ASP 1kW module. It is simply because stronger Mosfets are slower. New much faster Mosfets are introduced every year and bandwidth eventually will increase.

Magfan - I don't know if Mosfet configuration alone can be considered topology. Icepower uses full bridge vs. half-bridge on Hypex. Some people claim that full bridge sounds more "tube like" but also places half of the supply voltage on speaker terminals and in addition cannot be bridged.

Bobrock - Bass is one of the stronger points of class D. The issue is not if class D is best sounding but how does it sound for the money and if YOU like it. If there would be something really wrong with it (as Audiofeil implies) Jeff Rowland would not switch whole production to Icepower. Class D sound is very clean and revealing - will show deficiencies in your system.

As for the amp being "switching" or using switching power supply - every linear supply is in fact switching supply operating at 120Hz.

Main problem of class A/B is very high gain before feedback (up to 4000) that is about 10x higher than gain in class A amp (as low as 200). This high gain, in presence of limited bandwidth, is causing some overshooting on high slew rate pulses (TIM distortion). As a result of this amp produces/enhances higher order odd harmonics - that our ears are very sensitive to, making sound sharp/unpleasant. Tube amps on the other hand enhance even harmonics making sound wonderful on voice or guitar bad worse on instruments with complex harmonic structure like piano (sounds like out-of tune). Class D or A are likely neutral.

Dob - Sinclair produces class D audio amplifier called X-10 in 1964 (Designer: Gordon Edge)

Dod - I just wondered why you call him "inventor" when class D is known from 50's and Sinclair X-10 was sold in stores both as a product and a kit in 1964 (12 year earlier). It was followed shortly by X-20.

Samujohn - class D does not mean "not analog" - it is purely analog in 99% cases. The fact that output stage switches between two voltage levels doesn't make it digital because time and not the voltage is analog quantity here. Word "digital" was used by uniformed people and became popular name for class D. I don't have anything against calling it "digital" as long as you realize it is not.

As for digital inputs making amplifier "digital" it would be true for any amp. Combining in one box DAC and tube amp would make it "digital amp" - nothing to do with a class of an amp.

Rafael - Absolutely agree.

Al - I'm not sure what they do to obtain decent resolution. In order to get 16 bit resolution and 20kHz bandwidth with traditional PWM clock has to be 65536x20e3=1.3GHz. It is way to fast and no room to filter out carrier. They might play games with modulating power supply at the same time or creating more states (more Mosfets and more voltages). It is getting very complicated to get real digital amp. Pure digital might be not bad - just look at HDTV.

Al - Thank you for the link. My problem is with resolution. As you said TACT stated resolution from PWM is 8 bit. Where do they get required extra resolution (possibly by adjusting power supply?). 384kHz carrier sounds about right (Icepower is 400-500kHz).

Class D is here to stay. Some people don't like the concept of switching in audio but delta-sigma converters, SACD and DDS recordings are exactly that (PWM).

Al - they do, but carrier frequency is almost 10x higher and resolution is 16-bit. SACD pulse width modulates at 2.8MHz - said to be equivalent to 20-bit on non-oversampling system. My analog class D amp (Icepower 200ASC) runs at about 500kHz with unlimited resolution. There is no quantization noise since it is not a sampled system.