Hypex N core module

Here is an example of today’s switching frequency trying to be filtered by Mark Levinson No.53 with the $50k usd Class-D. They tried very hard by as you can see by the 4 massive x filter chokes added together (paralleled or series or both) to give a steeper filtering effect on the switching frequency, it worked as the 10khZ square wave shows, without the use of Stereophiles AUX-0025 passive low-pass low power filter, but adding filters together is well known to create other problems, this amp it seems was not a success for ML.

" However, the more I listened, the more the overall sonic picture seemed flat and uninvolving. An enigma.—John Atkinson"

ML Class-D monoblock x1 showing 4 x filter chokes.
https://i.pinimg.com/originals/f1/c5/3a/f1c53a9e8f03bd1ea3a4ed38f65c0b1e.jpg

ML Class-D 10khz square wave without Stereophiles special testing filter.
As you can see very acceptable for Class-D with no switching frequency ringing getting through those filters.
https://www.stereophile.com/images/1212ML53fig02.jpg

Cheers George

I completely agree that switching frequencies have to be increased!

But, the problem is not switching speed! The problem is how long it takes for the device to turn on and off, which is different. Because that takes some time, the circuit has to wait until the device has changed state before the other device can do its thing. That waiting time is deadtime, which increases distortion.

**That** is why you go with faster and more expensive devices; its all about keeping deadtime to a minimum.

Put another way, with conventional class D circuits, a switching device that can do 10MHz can only be used at a few hundred KHz before deadtime becomes the big impediment.

Now the parts we work with are not that expensive, but we found a way to eliminate deadtime. This allow us to switch at much higher frequencies.

Now the parts we work with are not that expensive, but we found a way to eliminate deadtime. This allow us to switch at much higher frequencies.

Ralph, what is the approx ringing of the square wave I linked to in the 1st pic, it is the switching frequency noise

Yes dead time is another problem.
But you will still have the problem, of eradicating the switching noise completely with the output filter without ANY effect on the audio band from 20hz to 20khz. So say a 10k square wave will look like the ML’s one I linked to above, without any Stereophile external bench filters used.

BTW I wish you luck on your Class-D quest, but Technics has shown the way with limited supply of the transistors they use. In the future there maybe a good supply to everyone with hopefully 3 x the speed of switching frequency. But i suggest not to jump on the gravy train just yet, wait for the technology to catch up, or the end maybe like the ML53.

Cheers George

We've already been listening to the amp. FWIW the squarewave response you linked does look pretty bad. Our tube amps can do better than that!

Obviously we're not letting this thing out without it doing what its supposed to do.

The thing is, you can have all sorts of issues when building a switching amplifier. The layout of the boards is critical- if not done right you can get stability problems. The little 'dimples' in the squarewaves you linked say to me that there is a suppressed oscillation in the amp somewhere. The squarewave should have been flat across the top, but its not! That's not a switching frequency thing as it is a stability thing.

Now the parts we work with are not that expensive, but we found a way to eliminate deadtime. This allow us to switch at much higher frequencies.

Naturally your not going to tell us how it’s done, I’m hope for you that you can do it, but also sceptical at the same time, as minds more attuned to solid state Class-D topology than yours have not succeeded, save for Technics who are half the way there.

Cheers George