High end Class D amps?

George - You've brought up this notion of EPDR in several class D threads, but haven't explained how it relates to class D. This is a term that was made up by a Stereophile reviewer to try to explain why linear amplifiers had a hard time driving speakers with a reactive load. Specifically, speakers whose current demands are not linearly related to the voltage across the speaker terminals. 

In a linear amplifier, this will cause a higher than expected thermal load on the output transistors because the high current demand can exist even with a high percentage of the rail voltage across the output devices. 

In a class D amplifier, the output transistors don't care about the voltage across the speaker since the voltage output only affects the duty cycle, not the power dissipation. They are constantly switching on and off at their oscillation frequency regardless of the voltage across the speaker. As long as the amp can handle the current demands, the fact that the load is at all reactive is irrelevant. 

If you disagree with these statements, please explain why. (And don't just repeat your previous statements since so far you haven't described how EPDR relates to class D). 

Obviously, you can contrive a situation where a given class D amp does not have the current capability to drive a particular load at the desired voltage, but this true with a class A or A/B amp as well. And, in fact, the thermal challenges are much more difficult with a class A amp, and even a class A/B amp, to meet a specific desired current capability.

George - You’ve brought up this notion of EPDR in several class D threads, but haven’t explained how it relates to class D.

It relates to any amplifier seeing the low EPDR loading which demands extra current to be delivered from the amp, which Class-D’s don’t do as well as good linear Bi-Polars can.

Obviously, you can contrive a situation where a given class D amp does not have the current capability to drive a particular load

I don’t contrive anything, it’s fact Class-D can’t do current into low impedances like good linear bi-polars can, and if you don’t believe or have the knowledge to understand that, it’s your problem not mine.

Now excuse me I’m going back to the workshop to finish off my 1973 Ducati 750 sport (round-case) engine main bearing replacement.

And Ralph in the below post below, it’s just not the GaN transistor wrong yet again, you forget the output filter and feedback also.
Just leave it be Ralph, anyone can see your in "product protection mode" your not doing yourself any favours.

So explain how an amp with an output impedance of 10 milliohms

Just like a Technics Su-G700 Integrated GaN Class-D with it’s milliohm output impedance also can’t drive the Alexia load either!!! It’s got the so called wattage at 4ohms

Back to the Duke, more important than talking to shillers of their own yet to be released amps. 

I’ll state once again as yet NO!! Class-D (and that also goes for my choice Class-D Technics SE-R1) will perform as good into a pair of Wilson Alexia and such, with their EPDR bass loadings like a hi current Gryphon Antillion etc etc can.

Just look up the 'on' resistance of any GaNFET. This will be the value of the output impedance of the amp unless it runs feedback- in which case it will be lower. So explain how an amp with an output impedance of 10 milliohms or less will care one bit about a 0.85ohm dip in a loudspeaker.

I’ll state once again as yet NO!! Class-D (and that also goes for my choice Class-D Technics SE-R1) will perform as good into a pair of Wilson Alexia and such, with their EPDR bass loadings like a hi current Gryphon Antillion etc etc can.

Interestingly enough, Michael Fremer reviewed the PS Audio Stellar M1200 amps in Stereophile this month. Class D Ice power amps. His exact quote in respect to bass performance when driving his Wilson Audio Alexx is "The M1200s ability to couple with, control, and drive the woofers of my Wilson Alexx loudspeakers matched that of any amplifier I’ve had here." Read that again, because he has had some pretty heavy hitters in that room driving those speakers. When he went to grade the individual aspects of the amplifiers performance he rated the bottom end as A+. When you read the review, you can tell he is pretty impressed with these $6000 a pair amps. The "whole product protection mode’’ thing is particularly interesting when the name of the product HE (George) builds is attached to every single post he makes here. Product promotion (or protection) at its finest more than 8000 times here.

There are class A/B amps that have been designed to output very high current levels at the expense of cost and weight, and thus far, class D designers have chosen to focus more on the mainstream market where current demands are not as extreme. But this has nothing to do with EPDR.

I'll grant you that there may be limitations in the number of output devices that can be paralleled and still maintain appropriate switching speeds. With current output devices, this may limit the maximum current that class D amplifiers can deliver to less than is possible with a class A/B design. I have not tried to design a class D amplifier myself (other than using an off-the-shelf module), so I don't fully appreciate the limitations, But I think the potential is still quite high even with current devices. 

For most reasonable speaker loads, the current demands are well within the capabilities of mainstream class D amplifiers, such as those built using the Purifi, Hypex, and ICEpower modules. The Purifi module, for example, can output 25 amps before the current limiter will kick in. Obviously, this still requires that you have a power supply that can deliver this level of current, as it does with a class A/B amp.