Class D amps are a confusing lot. Some call them digital, others do not.
Whether or not a class D amp is referred to as digital or analog is not related to its class D power output stage. What would properly be called a digital class D amp is one that can accept a digital input, and which puts that digital signal through some dsp (digital signal processing) to generate the modulation waveform that ultimately controls the switching of the class D power output stage. An analog class D amp would differ in that it would utilize an analog input and have an analog front-end signal path.
Some companies even tout the fact that they switch so fast that they are super, super fast, so they sound better. That is also a funny fact, since may people here have stated that increased sample rates in CD players, ( switching ), decreases sound quality.
My philosophy is to take claims of sonic superiority that are based on references to design parameters with several large grains of salt. At best the truth in them should be qualified with the phrase "everything else being equal." But everything else is almost never equal, because of the enormous number of tradeoffs, architectural decisions, parts selections, detailed design considerations, etc., etc. that go into designing and developing a product.
Not to mention that most such claims conveniently don't address the relation of those parameters to sonic performance in a quantitative way, that would provide some perspective on the degree of importance of the parameter.
Also, keep in mind that class D power stage switching rates have nothing to do with the sample rates of sampled data systems, such as the cd medium. In the latter, information is stored that directly corresponds to the amplitude of the audio waveform at specified intervals. In the case of a class D power stage, the instantaneous amplitude of the audio is implicit in the timing, not the amplitude, of the high-to-low or low-to-high transitions of its output. Those transitions are always the same (large) amplitude; it is WHEN they occur that defines the audio information. That waveform is then put through a passive low pass filter, which removes the spectral components associated with the switching, leaving (ideally) only the spectral components associated with the audio.
High switching frequencies conceivably could relax the sharpness with which that filter must roll off, potentially requiring a filter which is simpler, cheaper, and less likely to have anomalies in the audio passband (such as frequency response ripple or phase problems). For similar reasons, higher sample rates in a sampled data system may be advantageous, EVERYTHING ELSE BEING EQUAL. On the other hand, the presence of faster signals, particularly if the edge rates of those signals are correspondingly faster, raises the possibility of other problems such as crosstalk, emi, digital noise, etc., if the design is not done carefully and expertly. As is usually the case, the quality of the design and the skill of the designer tend to be more important than the particular approach that is chosen.
If the sound that is fed to our speakers is a product of the input being switched on and off, not matter how fast, then it is not analog, but what ??, even if the designers are claiming that it recombined, isn’t it always wanting to play catch up ??
Absolutely not, assuming good implementation. The switched waveform, when considered in the frequency domain, contains spectral components corresponding to the switching, which are at high frequencies, and spectral components corresponding to the desired audio waveform, which are at lower frequencies. In principle, there is no reason whatsoever that the audio cannot be perfectly recovered, by using a filter that separates the desired spectral components from the unwanted ones.
Upon looking at the power into 4 ohms, the power is less that the normal doubling of output we see in most class A/B, and class A amps.
I can't shed any light on that; sorry!
I’d really appreciate if some qualified technical people would reply, along with all the regulars.
So that you can properly calibrate my responses, I am a long-time audiophile, who has had no exposure to class D amps, and who has two degrees in electrical engineering, and several decades of experience as an electronics design engineer and manager (not in audio).
My bottom-line instinct with respect to Class D would be to approach it with caution. Its fundamental advantages are non-sonic (reduced size, weight, heat, and cost). It's application to high-end audio is recent and limited, and it is very conceivable to me that there could be many subtle aspects of good design, that would have subtle but significant sonic effects, that may not yet be commonly recognized by the designers or users of this type of equipment.
Hope that is helpful,
-- Al
