Hypex N core module

"if you want to have your product performing at the cutting edge it is not possible with today’s known switching technologies. In order to come close to the performance of the best linear design we would need high-current semiconductors that provide switching frequencies of several MHz or even GHz."

Several MHz isn't a problem. We're working with inexpensive devices that can easily do 5MHz and beyond. The problem is deadtime. That has so far proven to be the switching limit; that's why they don't switch much higher than maybe 2-5MHz tops. The deadtime increases distortion, and the faster you switch, the more you need it- so there is a minimum distortion that you can hit, sort of like Whack-A-Mole. I did state this in my previous post.

When you are switching that fast though, the speaker itself is part of the filter; there's no problem getting a filter to work and it won't burn up.

Here are the 10khz waves of Class-D both done by Stereophile tests, one with and one without the Stereophiles special AUX-0025 passive low-pass low power filter.  This filter can't be used while listening as it would burn out almost instantly.

With the special bench test filter:
https://www.stereophile.com/images/916BC600fig2.jpg

Without the special bench test filter:
https://www.stereophile.com/images/1212AM1fig02.jpg

Now I ask ANY linear amp manufacturer, would they be happy if their amp gave a 10khz square wave that looked like the second pic to sell to the public.

Cheers George   

Several MHz isn't a problem. We're working with inexpensive devices that can easily do 5MHz and beyond.

Technics have produced a Class-D amp (SE-R1) that has double today's switching frequency speed so the output filter has less of a chore to filter it all out, but it's $30k usd and special order only if your the God or Emperor of Japan?

This amp is half the way there because of the special hi speed semiconductors used to get double the switching frequency of 1.3mhZ

It's getting there, but needs to be double d again.

Here is one reviewers take on the Technics Reference SE-R1 Class-D amp:

" No other audio system that’s graced our listening room here at DT has captivated and mesmerised our staff quite like Technics Reference system. Seriously, some of us are having trouble getting our jobs done because we can’t peel ourselves away. This is the sort of audio system that you must hear to understand. Listening to tracks that we’ve heard 100s of times — and on excellent systems at that — is now a revelation of once hidden nuance and detail. Not only are we hearing things we’d never heard before, we’re hearing it in a way we’ve never heard it before."  

Cheers George   

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.