Competitive class D amp suggestions

Electric engineers succeed to develop exceptionally sounding equipment, but the existing parameter for measuring their ``distortion'' seem to me to be useless. 

Engineers have other measurement tools: distortion vs frequency (rising distortion is an indication brightness and harshness may be present), distortion spectra at one Watt and also at 06dB of full power and distortion spectra measured at different frequencies.

If you know what you are looking for, these measurements can tell you how the amp will sound. I agree THD isn't a good marker.

Engineers have other measurement tools: distortion vs frequency (rising distortion is an indication brightness and harshness may be present), distortion spectra at one Watt and also at 06dB of full power and distortion spectra measured at different frequencies.

If you know what you are looking for, these measurements can tell you how the amp will sound. I agree THD isn't a good marker.

So the situation is not completely hopeless. Ralph, how these distortion parameters reflect the distortion of the harmonics of each degree?   I think that now i know that i am looking for an amp with small first order distortion but large second and third order distortions, roughly. But, as I have also mentioned, i don't really know how large they can or should be, no idea at all.  

@niodari 

the numbers might get you in the right theater but you will only find the perfect seat by trial and error because the amp has to mate with the source or preamp and speakers in a way that sounds great to you. 

So for the trial and error process you either buy new and return or preowned and resell if the amp ends up being a bust.  The key is to enjoy the journey knowing that perfect is the ultimate unobtanium.  

So the situation is not completely hopeless. Ralph, how these distortion parameters reflect the distortion of the harmonics of each degree?   I think that now i know that i am looking for an amp with small first order distortion but large second and third order distortions, roughly. But, as I have also mentioned, i don't really know how large they can or should be, no idea at all.  

In a nutshell, if there's enough lower ordered harmonic distortions, they can mask the higher orders. The higher orders otherwise cause harshness and brightness. Either the 2nd or 3rd can predominate, but if the 3rd dominates then it has to be at a lower level to begin with- about 1/10th what you might see if the 2nd were dominant in the design.

For example almost any SET makes 10% THD at full output- most of which is the 2nd harmonic. If you have an amplifier design that makes the 3rd instead of the 2nd (which can happen if the amp is fully differential and balanced, since even orders are cancelled throughout the design) then the THD will and must be much lower. This isn't that hard to achieve since a design that exhibits a dominant 3rd harmonic will tend to have less distortion overall anyway.

On top of that the distortion cannot rise as frequency is increased, which is a problem with most solid state amps made (and with tube amps employing feedback). Class D offers a solution for this- you can have the distortion vs frequency look like a straight line, and you can run a lot of feedback at the same time. In this way you can achieve distortion levels that are several orders of magnitude lower than you might see in a tube amp ye the actual distortion signature (2nd and 3rd vs the higher ordered harmonics) can look quite similar to a tube amp.

This allows greater transparency (since distortion obscures detail) yet the same kind of smooth mids and highs you associate with a really good tube amplifier- IMO, the best of both worlds.

In case you don't get my drift, I'm drawing a very straight causal line between the distortion measurements and how the amplifier actually sounds; IOW its predictable based on sufficient measurement! The tech to do this really didn't exist 40 years ago but it does now. A lot of audiophiles don't know that yet; like so many industries tradition plays an enormous role in this.

In unrelated news, Topping has recently released a new version of its D90SE DAC, called the D90LE, and that is unremarkable in the current context.

What may be of interest, perhaps for educational purposes only, is that included in the new firmware is the option to simulate either tube harmonics or transistor harmonics (or neither).  Specifically, just 2nd and 3rd harmonics, fixed for either option.

Scroll over three quarters way down here to "Sound simulation", and there are images of the fundamental and its two prominent harmonics spikes (sadly the images are not very clear).