[quote name='Phil Starr' timestamp='1456406515' post='2988639']
There's nothing inherently wrong with class D amps. Make a decent recording of an Ampeg/Trace Elliot/70's valve amp and play it back through a really good PA and if it had 'heft' then that will still be there, much louder if the engineer likes it that way. The PA will probably be operating on class D amps but they may be capable of 000's of watts. So it isn't class D per se, they certainly don't need to be gutless and they'll handle any amount of bass.
Lack of 'heft' then isn't to do with class D. I don't like the term because it is meaningless but so many people perceive a lack of something. So what are they missing?
Well it could be distortion as some people have said or it could be a non flat frequency response, but emulators should be able to get most of that back. The plugins used in recordings do a fairly good job nowadays, they may not exactly match an Ampeg stack but I'd venture that most of us are capable of being fooled once it is in the mix.
So, if I'm right what we are talking about is the implementation of class D. Plus perhaps some placebo effect (if an amp is heavy enough it will have heft!!!). With class D the designer can offer you almost limitless power at low cost in the amplifier stages. The question is how much capacity to put into the power supply. You are probably only going to need it for peaks, too much power and you'll be blowing the speakers. Why put an expensive power supply in if you are only needing it for a few milliseconds now and again? For PA amps it is much simpler, distortion is the enemy, mainly they operate in a predictable environment so an amp that delivers 300W continuously but will peak at say 1000W makes good sense. I suspect a lot of the power output stages of the current crop of lightweight heads are borrowed from modules developed for PA with a bass orientated preamp/tonestack grafted on. It may well be that some or all of the top five brands of lightweight amp all suffer some restrictions in their abilities to deliver continuous power built into their power supplies or their protection circuits. I can't see how Class D amps are inherently worse than AB amps though.
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My criticism of 'Class D' is exclusively aimed at the consumer-level modules used in the bass head market. Not the pro audio stuff.