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Class D Switching Power Amplifiers and Power D/A conversion

Breakthrough DD amplifier?
Breakthrough DD amplifier?
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Old 12th February 2019, 03:12 PM   #21
ds23man is offline ds23man  Netherlands
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News-Pre-launch of Lyngdorf MXA-8400 | Lyngdorf Audio


Its a refinement of Ncore. No digital direct drive or a numerical amp.
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Old 12th February 2019, 03:23 PM   #22
Bruno Putzeys is offline Bruno Putzeys  Europe
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Default Just a quick note from my end to reduce the speculation

I must apologise I won't be able to join the discussion further after this post, because things are a bit busy here. Meaning that if anyone misunderstands what follows, I shan't be here to rectify matters

The amplifier is not "DD". It's a straight self-oscillating fully analogue design, like all of my work of the past 15 or so years. All that time I've been saying that this is the best and most elegant way forward, and I daresay the new circuit confirms this. We've decided to call the technology Eigentakt, which is an obscure German term for self-clocking or self-oscillating. That would have been a giveaway, had Peter thought to mention the word.

I guess folks were assuming that digital was involved simply because the person to break the news is Peter Lyngdorf and he's of course historically been involved in open-loop "PWM power DACs", which is what I suppose you mean by DD. And of course, the technology historically used by Lyngdorf was developed by Lars Risbo who's my twin brother in this new venture, Purifi. He too feels no particular need to stick to digital control for its own sake. Being an engineer like me he's happy to use whatever seems the optimal solution at a given time.

So what's new in this amplifier? One thing is that I've developed a sampled domain model for self-oscillating loops that remains valid for all duty cycles, so it can predict closed loop response exactly under all conditions. This then allows finding a loop design that has very high loop gain (about 75dB at 20kHz, which is 20dB better than my previous designs) without running into stability problems near clip. A design procedure like this can't be patented because you can't prove that someone has been using it, so in a break from past style I'm not going to publish any details of this mathematical model. It's a trade secret, plain and simple.

Then there is the loop structure that allows better control of the closed loop frequency response. My previous amp* has approximately a 1st order roll-off. Now, since the output filter naturally has a second order roll-off it means that this amp could be overdriven with out of band noise from e.g. DSD recordings (in fairness, only when you cranked a quiet recording high). Also a first order response already droops noticeably by 20kHz which was sometimes remarked upon by numbers people. Eigentakt has a well-defined 2nd order response which stays dead flat in the audio band and rolls off in a fully controlled manner with a sensible -3dB point of 60kHz. The loop structure used to get this behaviour is subject of a patent application. A few other items are not really germane at the moment but were worthwhile enough to put in a separate patent application.

From a practical perspective, the enormous loop gain is partly used to allow more relaxed timing of the power stage without paying for that in distortion performance. As a result, the 400W power stage only has an idle loss of 1.7W or so. From dire experience I've learned that people don't perceive an amplifier as "cool running" if the idle losses aren't super low. It seemed a sensible move to get that sorted for once and all. In other words, the measurements you're seeing are those of a power stage actually optimized for idle loss (and hence, efficiency under real listening conditions).

Those asking "where are the patents", patience. It's a long procedure. First you file an application that gets bounced back and forth between the inventor and the patent office (with a patent lawyer in the middle), and 18 months after the first filing you see a published patent application. No sane inventor publishes details before that - those 18 months are actually there so you can take advantage of legal protection without having to tell your competitors your secrets. In other words: you will never find a patent for download when a new technology is announced. Of course, in sales communications one will easily say "patented" but actually it would be more correct to say "patent applied for" which should be enough of a heads-up for potential copycats.

Finally a note on how the various companies fit together. Purifi ApS was founded by Peter Lyngdorf, Lars Risbo and myself. No shares are owned by any of the other companies we're involved in. Purifi is run independently and will eventually supply technology to a broader base of customers. But it should be obvious why our lead customers would come from our own orbit...

*Forming a new company of course involved quitting my previous position, which I'm now competing with. I think it's only polite not to bandy around any of their trade names, in particular since in private we're still friendly.
There's a time for everything, and this is not it.
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Old 12th February 2019, 05:45 PM   #23
Antoinel is offline Antoinel  United States
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Breakthrough DD amplifier?
Hello Mr. Putzeys,

Congratulations to the inventors for this recent achievement. This invention is expected to be better than your past US 7,113,038; which itself [and its amps] is remarkable in its own right.

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Old 13th February 2019, 02:47 PM   #24
MorbidFractal is offline MorbidFractal
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Originally Posted by Bruno Putzeys View Post
I must apologise I won't be able to join the discussion further after this post, because things are a bit busy here. Meaning that if anyone misunderstands what follows, I shan't be here to rectify matters

Blah snipped.

Given you have immediately exited the conversation I will not explain just how well I do understand the part that has been snipped and its implications. There is a chance we may have to "rectify matters" at a later date.

Last edited by MorbidFractal; 13th February 2019 at 02:52 PM.
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