Class D = Trash?

Tim, Thank you.

I think a bit more valid conclusion as to which type of power supply is better is to have the same amp with SMPS and then the same amp with analog power supply given EVERYTHING else is equal. I emphasize everything is because as you would agree a front end and/or a preamp or even speaker wire can influence the sound, for better or worse. First, let me clarify that there are two fundamental differences between the two type of power supplies we are discussing here.  One being the SMPS and the other is the traditional analog power supply and that is obvious. But another big difference which is also worth mentioning is the SMPS type is being regulated...Meaning that the output voltage is held constant as long as current draw from the load (the amp) is within the supply's design capability.  And that is very desirable in audio power amplifier design or anything electronic for that matter.   However, regulated analog power supply for high power amplifier is very expensive to design just from the standpoint of hardware involve.  This is the very reason why regulated analog power supply is mostly done in preamplifier circuit since power involve is not huge, compared to Power amplifier.  In fact, 99.9% of power amplifier out on the market have been designed using an unregulated analog power supply, at least for the output stage. A fewer design may have a regulated analog power supply for the input and maybe a driver stage, but power supply for the output stage still is unregulated.  Stable voltage supply rail is highly desirable since changing voltage supply rail can change biasing current in conventional discrete transistor design especially.  Also, change or reduced in voltage supply will also limit how far the signal can swing, after all the amplified signal can only swing as far as the available supply voltage rail, and as  a result power is reduced.  Though the first effect (changing voltage under dynamic condition) is much more detrimental than the secondary effect of reduced power IMHO.  Due to those effects mentioned the result will turn for the worst in the final sound through the system. This is the fundamental reason (not the only reason of course) why most power amplifier can sound quite good at low volume but falls apart when pushing hard at high listening level, and especially into a difficult speaker load, because an unregulated power supply will sag (drop in voltage level) under heavy current demand from the load. While the analog power supply we are discussing here is not regulated, though it can be.  From my experience, an regulated analog power supply is always better than an unregulated analog power supply, again given everything else is equal. Then again, there used to be a debate( isn't it always with audio :-)) that an unregulated analog power supply can actually sound better than a regulated one.  Note that so far I have made a differentiation between a regulated and an unregulated ANALOG power supplies and not SMPS.  SMPS by design is always regulated.  Please note also that so far I have only mentioned power supply topology but in regard only to conventional discrete transistor design as in typical Class A and Class A/B design and not with PWM switching amplifier.  As mentioned above I preferred a regulated analog power supply for conventional discrete transistors design, simply because in class A/B and especially class A, always draw current constant current, and can be lots of it if it is class A or a heavily biased class AB. The reason is simply that if the supply is not regulated, the voltage rails will sag significantly resulted in lots of ripple on the DC rails.  And the end results will end up with is noise, hiss and hum.  And this is only under static condition (no input signal so no amplification), and will get worse under heavy dynamic condition where heavy current demand is asked for.  And that is very true for class A/B power amplifier.  But what we are talking about here is switching amplifier.  There is no constant current being drawn here as in the case with conventional amplifier. Well, there is but very tiny amount of current being drawn. The amp only draws current when there is signal.  But more importantly when it does draw current, but unlike conventional design, the transistor does not spending so much time in the linear region because the output stage acts like a very (make it extreme) fast switch.  And therefore, there is not much power dissipation as heat is being generated.  So this is the very reason why it runs so cool and efficient as we all know about class D amps.  So for Class D I really think the important thing is to be able to deliver huge amount of current but FAST and as fast as you can and not so much of being regulated or unregulated.  Though I got to admit that my intuition tells me from experience that a regulated analog power supply (mind you) even for the output stage would give a better result. I don't know since I have not tried it neither with SMPS nor regulated analog power supply, with class D that is. I have tried it with conventional design and for sure regulated supply wins hand down. There is something about switch mode power supply which I need to investigate further.

OMG, I can't believe I went this far and still have not answer Tim's question :-).... So without dwelling into too much of all of the technical jargon, the short answer is YES!!! at least what I have tried so far with class D.  I apologize for the post being too long, and in all honesty, this is the very reason why I decide not to anticipate with most of the discussions through the years as this took me hours to compose something like this as I am not a very good writer.  Though I found most of the discussion very interesting to say the least.

There is one confession which I need to make and that is coming from conventional strictly pure class A design through the years, I always chuckle and LMAO at time when I read debate where a piece of wire would make a difference in the final sound.  Well, I have stopped laughing ever since dealing with Class D.  Boy, talk about temper.  Just a simple bypass cap, which used to make tiny (if at all) difference in sound with conventional design, but with class D? It can sound heavenly or like trash.  The same goes for type of rectifier being used, and the wire and ....
 And for the record, the H2O has regulated analog power supply for the front end and unregulated power supply (and huge at that) for the output switching stage.  Also, I have finally manage to get a pair of the NCore 400 modules and have implemented them with a similar power supply which I have implemented for the H2O using Icepower module. I have been listening to the Ncore and have been rotate the Icepower in and out from time to time for comparison for the last month or so. Now what I need is to have is an NCore with switching mode power supply which design by hypex for real comparison.  Hopefully I would have a better insights on the difference in sound.

Henry

Henry, thank you. While I understand only half of what you're talking about, the detail and knowledge in your post is superb.

The points  @h2oaudio makes about regulated vs. unregulated are pretty much true. VERY few analog amps are regulated at all. Krell did this with the FPB I believe. Sanders's Magtech is what I would call semi-regulated. Brilliant compromise.

Doing linear for a carefully implemented input section also makes a great deal of sense if you want to get the best you possibly can out of it, without requiring a massive investment in hardware that a fully regulated amp would need.

Best,

E

One interesting experiment I read about I've wanted to try is to actually LISTEN to the amplifier power supply lines. The + and - supplies are, in theory, at fixed DC voltages but as the music plays, the current draw will cause the supplies to sag with each note. You can actually attach headphones (carefully, wth appropriate circuits) and hear just how much effect driving speakers has on the power supply.

This technique can be further expanded to analyze the actual frequencies that the supply is worst at isolating, and to add appropriate filtering. A fussy technique I don't know if anyone but one vendor (probably out of business) has ever done. Still, fun idea.

In stereo amps, this effect is probably one of the main reasons for increased cross-talk between channels.

Todd, Thank you.  But I admit my knowledge is very limited actually compared to some of the GODS of amplifier designers such as Nelson Pass, John Curl and quite a few other designers.  I am a rookie compare to these amplifier designers.  I just know enough to make the amp sounds halfway decent by lots of experimentation.

I sincerely hope I did not offend anyone with some of the statements I made.  Please remember that my opinion is just that...one opinion.  It is just happen that I am a manufacturer.  And more importantly, what I referred to as "BETTER"  is only in the context within my system and others system which I heard, and furthermore to my ears and my ears only.  I do believe lots of members on this board have been around long enough to know, that there was not, is not and will never be one absolute.  It will always depend on the system as whole and more importantly listener's preferences, type of music, room acoustic and the list goes on.  And to answer the OP's questions.  The answer is NO.  Far from trash actually.  Then again, just like what I just mentioned above.  It depend to whom are we asking?  So the correct answer I believe is YES AND NO :-).

Henry