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Class D Switching Power Amplifiers and Power D/A conversion

Ncore design refinement
Ncore design refinement
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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

https://lyngdorf.com/wp-content/uplo...fact-sheet.pdf

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...

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*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.
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Old 12th February 2019, 05:45 PM   #23
Antoinel is offline Antoinel  United States
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Ncore design refinement
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.

Best
Anton
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Old 13th February 2019, 02:47 PM   #24
MorbidFractal is offline MorbidFractal
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Quote:
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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Old 24th February 2019, 04:56 PM   #25
Antoinel is offline Antoinel  United States
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Hello All,

My post is not meant to speculate on the upcoming patent by Mr. Putzeys et al. I'd like to comment on Mr. Putzeys US Patent [7,113,038]. It is entitled "Power Amplifier" and was dated Sep. 26, 2006. Please note:

1. The left view picture is page 2 of this patent. Focus on Fig.2. I do not know whether Fig.2 pertains to the commercial Ncore amplifier; but it is suitable for this following discussion.

2. Fig. 2 struck me as an Analog Power Amp with an intentional self oscillating ability to make it Class D. Can I [in theory] improve it? Maybe as follows!

3. The right view picture is the basic schematic of Fig.2 plus the inclusion of Positive Current Feedback [PCF] therein. This is the hypothesis which is meant to improve the performance of the resulting amp.

4. Rsense [~0.3 Ohm] is connected in series with the loudspeaker load [Zl]. It senses load current as the resultant Vsense; which is the [PCF] signal. The phase of the input signal to the comparator, the power output signal and that of Vsense are in alignment [in phase].

5. Vense is sent to the non-inverting input of the comparator via Rin [given as 47 K].

6. PCF increases the intrinsic open loop gain of the parent amp. Its value is it gives the new amp more gain to sacrifice at a constant overall negative feedback due to Rf and Rg. Thus, the resultant amp is expected to have a lower output impedance [higher damping], and a lower distortion than the parent. Output noise may rise!

7. A side effect of PCF in this [theoretical] amp is its propensity to oscillate beyond a certain level of Vsense. Self oscillation may be a plus; after all this is an important function of Rl and Cl in Fig. 2 of the parent amp. Can one do without Rl and Cl; but add a generous level of Vsense so as to enable a simultaneous self oscillation?

I hope the above is a possible food for thought and entertainment.

Best
Anton
Attached Images
File Type: jpg PutzeysUS7,113,038.jpg (189.0 KB, 901 views)
File Type: jpg PutzeysUS7,113,038with PCF.jpg (218.2 KB, 904 views)
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Old 27th February 2019, 03:46 PM   #26
mocenigo is offline mocenigo  Germany
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It would be interesting to know whether the output devices are GaN, and the switching frequency, but I suppose that this information is still kept under lid.
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Old 27th February 2019, 03:50 PM   #27
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Antoinel View Post
6. PCF increases the intrinsic open loop gain of the parent amp. Its value is it gives the new amp more gain to sacrifice at a constant overall negative feedback due to Rf and Rg. Thus, the resultant amp is expected to have a lower output impedance [higher damping], and a lower distortion than the parent. Output noise may rise!
ANY pos feedback increases the open loop gain. What is the reason that you specifically want to use current feedback?

Jan
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Old 27th February 2019, 03:51 PM   #28
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by mocenigo View Post
It would be interesting to know whether the output devices are GaN, and the switching frequency, but I suppose that this information is still kept under lid.
Buy one and see what type the transistors are, and measure the frequency.
Then tell us ;-)

Jan
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Old 27th February 2019, 09:38 PM   #29
jgazal is offline jgazal  Brazil
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Is this new refinement going to be available in diy kits?
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Old 28th February 2019, 12:15 AM   #30
Antoinel is offline Antoinel  United States
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Quote:
Originally Posted by jan.didden View Post
ANY pos feedback increases the open loop gain. What is the reason that you specifically want to use current feedback?

Jan
Thanks for your post. I fully agree with your statement regarding using positive voltage feedback [PVF]. No specific reason to choose PCF over PVF. I've played with both feedback types in analog power amps. Both are worthy of experimentation in Class D to possibly determine an edge for one type or the other.

Best
Anton
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