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

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.

Magfan: The new NAD M2 ... operates in the digital mode, which I expect to be the real definition of 'digital amp'.

Agreed 100%. My previous post was not worded as precisely as it should have been, to the extent that it implied anything different than your statement quoted above.

The signal path through a digital Class D amp will consist entirely of either digital signals or switched waveforms, from the amp's input to just before the low-pass reconstruction filter which reconstructs an analog waveform at the amp's output.

However, the literature at the Tact site appears to indicate that their amplifiers do exactly that. For instance, see the section on page 8 of the 2150X Manual entitled "How Does It Work."

I know of no other Class D amplifiers besides the Tact's and the NAD which you mentioned which can properly be called digital amplifiers, although there certainly may be a few isolated exceptions that I am not aware of.

Best regards,
-- Al

Hello Kijanki,

May be word "inventor" in not the most accurate - however, as I have illustated with the quote from "50 Greatest A/V Innovations" over last 50 years - John ULrick is attributed for bringing class D into HIGH FIDELITY audio, specifically in conjunction with his Infinity speakers which I believe were considered one of the best in 1970's. I believe that Spectron amplfiiers today are also one of the best among powerful amplifiers but this is besides the point.

All The Best
Rafael

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.

Pure digital might not be bad? It's not that good- yet. As for HDTV- I saw a demonstration of Sony's analog HDTV at the Chicago CES in 1989. It was amazing. Today's digital HDTV has a ways to go yet. Just look at the lack of low level detail in dark scenes. I also see pixelation in fast moving scenes in HDTV broadcasts, but not in 1080p blu-ray material.