Is D for Dry? Class D...

It’s nice all the Class D detractors have a thread to dump in.

There are different types of Class-D detractors, some only "dump" on those ** claims made by shillers of certain brand Class-D’s, who have no idea what they claim, especially in regards to what types of loads they are capable of driving.
If they didn’t make these false ** claims, there would be no confrontation from those detractors.

I for one have heard certain Class-D amps sound great, "with the correct speaker", and have acknowledged it here on Audiogon.

Cheers George

I do not see claims being made, but people expressing what they experience hands on there is a difference.

The "correct speaker" applies to any amp regardless of class and not just class D.

George goes on about this EPDR thing. But he's not clear on what the impact will be on a class D amplifier other than saying that they won't drive it.

Almost any class D amp made today has an output impedance that is often a good order of magnitude lower than traditional class AB designs. This is because the On resistance of the output devices is (especially if GaNFETs are used) literally only a few milliohms (our amp has an output impedance of 10 milliohms as an example). When you have an output impedance that low, if a speaker has an effective EPDR that causes it to be effectively slight less than 1 ohm the class D amp will still behave as a voltage source while driving it. This is for the simple fact that at 1 ohm the class D amp may well have a damping factor of over 100.


That's not the same thing as the amp falling flat on its face! However there is a chance that the class D amp will go into current limiting mode to protect the output devices. GaNFETs are tricky to heatsink and as a result the heatsinks you have to use are unlikely to move heat away from the output devices fast enough to prevent failure when driving such a load. So the prudent designer will have some sort of protection circuit even though the output devices can easily handle the current.

As I've pointed out a good number of times in the past, the limits of class D amps to drive a low impedance are the same as they are for a conventional class AB amp: current rating in the output devices, current available from the power supply and heatsinks enough to move heat away from the output devices.


Ironically its the GaNFETs that George has been so enamored of in the last couple of years where this heat problem is most likely to occur; conventional MOSFETs are often packaged in a TO220, TO240 or other package that can be easily heatsinked.


Now we should be clear about one other issue regarding EPDR. In most speakers the region where this might be a problem is often just a very narrow range of frequencies, IOW not the entire impedance curve of the speaker! If this is the case with a speaker that has such a low EPDR rating, it won't be much of an issue for a class D amp because there just isn't enough energy needed  over this narrow range to heat up the output devices. The Wilson Sasha and Sophias are good examples of speakers of this, and in practice mean almost nothing to any class D amp. At most clipping onset might occur slightly quicker, but frequency response is unaffected.

George accuses me of shilling nearly every time I explain anything about class D, so I reiterate that what I've said in this post has to do with most class D amps that are available today.  

Go and read any thread and you'll have georgie calling anyone a shiller who doesn't agree with him. It's his fallback accusation.

Before long, he'll be calling you sunshine, which in Australia, is a big insult due to it's effeminate connotations.

Next, he'll use **** notations in his spelling to use curse words to get around the mods.

Aside from that.....

All the best,
Nonoise