New Class D amplifiers

The main reason AB exists is to reduce heat and power consumption, with some of the benefit of class A operation.

And the main reason D exists is to reduce heat and weight, while (hopefully) retaining some of the benefits of AB operation. But the gold standard sonically remains A. Where heat/weight is not a consideration (eg., preamps) class A is the norm.

If you take an amp like the LSA Voyager......you can make it sound way more liquid and musical and detailed by changing parts and eliminating parts......and this CANNOT be measured. The amp will measure exactly as it does stock. The amount of measured distortion or the types of measured distortion are just one indicators of sound.....not sole indicators. You can send me 5 pairs of Atmasphere amps and I will mod each one differently and you will hear them as all different sounding and they will all still measure like stock......this is the truth. To think we can measure everything we hear is simply NOT TRUE. Can you tell me how an interconnect SOUNDS via measurement?.......NO, YOU cannot....because all cables measure basically the same (minor amounts of capacitance and inductance differences). Even Belden make a line of audiophile cables called Iconoclast.....made by a very scientific kind of guy.......but they have three levels of cables.....basic copper, OFC copper and PCOCC copper......EVERYONE agrees that the PCOCC copper one sounds best.....yet the cables are all made the same except for the wire purity........and they measure the same. Same with everything in an amp......you cannot measure the filter caps on the output of a class d output stage but every brand will sound different and also if you put the outside foil to ground (it will sound better.....and still measure the same). This game is infinite.

@atmasphere :

In addition, the distortion of the output section isn't made in the same way that it is in a class A or AB design. The result can be that the distortion the class D amp generates can be far more benign to the ear. 

Very interesting statement; would you please elaborate on this? What kind of distortion does a class-A's output section produce that the class-D is less vulnerable to?

But the gold standard sonically remains A. Where heat/weight is not a consideration (eg., preamps) class A is the norm.

This statement is false. What is the 'gold standard' is a benign distortion product, one that allows the amplifier to be smooth, fast and detailed all at the same time. That may or may not be a class A amplifier; any amplifier is easy to mess up if feedback is poorly applied and this is often the case.

Very interesting statement; would you please elaborate on this? What kind of distortion does a class-A's output section produce that the class-D is less vulnerable to?

I cannot speak for all class D amplifiers; in our class D amp, the two sources of distortion are the encoding scheme and the use of deadtime (to prevent the output section from overheating due to finite turn-on and turn-off times of the output devices; if both are on at the same time you get 'shoot-through current' which can heat them up quite rapidly to eventually fail) in the output section. In our circuit, these non-linearities produce lower ordered harmonics rather than higher orders. Because the lower orders are benign and innocuous to the human ear, the result is a smoother sounding amp that sounds a lot like a tube amplifier- the distortion signature is really similar.

A class A amplifier, because its output section is not perfectly linear, will generate not just the lower orders but the higher orders as well. The class A operation is used to put the output device or devices in the most linear operating region, but that isn't the same as saying its actually linear and no class A output section is, so it generates distortion.

Again:

The ear is keenly sensitive to the higher orders since it uses them to sense sound pressure. This is why an amp with THD of 0.01% can still sound harsh, if the higher orders are not masked by lower ordered harmonics. The assigns tonality to all forms of distortion and higher ordered harmonics are sensed as harshness and brightness. 

I currently have and use a Parasound A21+ amp and became intrigued with the idea of these new Class D amps. So without even hearing one I purchased the NAD M23 amp. Should be in within a couple of weeks and I cannot wait to compare the two.