The Truth about Modern Class D

By definition, zero deadtime means that the devices must be both on and off at the same time, a physical impossibility given any reasonable technology.

:) that is why we have a patent filed. Difficult takes a while- impossible is just a bit longer.

A Class D amp with Zero dead time is likely an amp with a short lifespan.

So far they run stone cold even when on for days on end.

The problem is not dead time, or notch distortion. The problem is audibility and connecting that to any particular technical choice. 

What I mean is, all amplifiers, even all musical instruments, have "flaws." To some they may not be flaws, to some they may be "attributes." We can argue about them forever but the importance of any flaw has to do with it's audibility. 

We can talk about ways to mitigate "dead time" forever, but that does not make the issue audible. 

One thing that Revel and Bose both do incredibly well is to pay attention to technology not for it's own sake but for audibility and desirability. We could learn from these approaches. 

Best,

E

The quote from Mr. Hammer is false. Here’s why:

As @merrilaudio states, the problem is dead time.

And the rest seems like an ad.


It’s not false as Ralph would have you believe.

It is "also" a problem, but isn’t the "major problem", and the cause is of what many dislike what they hear in the upper/mids and highs which is a product of the switching noise and it’s associated filter.

It is believed that the dead time will also be vastly improved with a 3mHz switching speeds.

This analogy from Nelson Pass will help:
"Imagine that the two transistors are runners in a relay race and that the signal is the baton they carry. In a real relay race, the runner receiving the baton begins running before the hand-off, which is made with the runners at speed. The runners who hand over the baton at a dead stop will operate at a severe disadvantage".

(if that runner can stop on a dime from full speed, then take off like a nitro drag car, you have higher switching speed)

And an interview with the great man (Nelson Pass) just a couple of months ago;

JS:There has been an explosion in high-end Class D amps in recent years. Some companies now market some fairly sophisticated – and expensive  – Class D models. Pass currently manufactures Class A and AB lines only. What are your thoughts on Class D?

NP: Personally I think it’s a miracle that they work at all, but then I think that about my phone, too. I have great respect for people who can make Class D amplifiers sound pretty good, and for delivering low cost, high power, and efficiency. They have earned their place in the industry.

That said, I am not tempted to go in that direction.

Cheers George

The problem is not dead time, or notch distortion. The problem is audibility and connecting that to any particular technical choice.

Dead Time has nothing to do with notch distortion, but the chance exists that I mistook the gist of your comment.

It’s not false as Ralph would have you believe.

It is "also" a problem, but isn’t the "major problem", and the cause is of what many dislike what they hear in the upper/mids and highs which is a product of the switching noise and it’s associated filter.

It is believed that the dead time will also be vastly improved with a 3mHz switching speeds.

George, you've not thought this thru. You are correct that by increasing switching times you can decrease distortion. However, its not the filter that is an issue, in fact as the switching time goes up, there is a point where the inductance of the load is enough to eliminate the requirement for a filter!
(Usually the filter fails to remove all the high frequency component. This component is known as the 'residual' and if the filter is designed properly, will be a sine wave of low amplitude. As such it will not interfere with other equipment and is far too high to be heard!)
Now as you go higher with switching frequency, distortion goes down, but with any particular switching device- oh- I'm repeating myself; here's my comment that you apparently didn't read from above:

The problem is that dead time causes distortion. So with any given output device, there is always a certain minimum distortion and associated maximum switching speed.

Nelson's analogy is correct however, so imagine not having to wait for a transistor to shut off before the other one turns on! Now we can switch at much higher frequencies and with much less expensive parts. Alternatively, an amp with a lower switching frequency but no need for dead time can have distortion as low as an amp that needs the dead time and is switching considerably faster.

You might dislike the whole lot instead *Grins!*

Why? ... "BECAUSE!"

G.

It's simple G
As it stands now the switching frequency noise output filter, has phase shift effects that reach right down to 5khz, that doubled for the worse at 10khz and doubled worse again 20khz. That's what many listeners find objectionable, in the upper mids and highs.

If the switching frequency is moved much higher from the present 400-600khz to 2 or 3mHz, then the filter can be moved up accordingly. So it has no phase shift effects down to 5khz, but only then at over 20khz instead where it really doesn't matter.
And the dead time will magically improve as well, it's a win win, for higher switching speeds that's why Technics with the SE-R1 persevered to get it, at a cost rrp $30k aud. 

Cheers George