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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 18th April 2019, 08:30 PM   #41
Antoinel is offline Antoinel  United States
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Ncore design refinement
The previous post showed a prototype which self-induced a loudness boost of the loudspeaker's bass; because of the application of positive feedback.

The attached schematic shows another prototype using the same components which self-induces a loudness cut of the loudspeaker's bass; because of the application of added negative feedback. Please note:

1. The magnitude of overall negative feedback which is inherent in the parent UcD180LP was increased; predominantly in the bass region. This has consequences; meaning [in part] a decrease in the magnitude of UcD's [Vout] at a constant magnitude of input signal [Vin]. Aka a cut in loudness.

2. The signal [V feedback] which develops across the sense resistor [0.2 Ohm] drives the non-inverting port of the Op Amp [OPA134A]. It has a line on its shaded portion to distinguish it from [Vin].

3. Assume that the output impedance of the source's input signal [Vin] is low [say ~100 Ohms]. The Op Amp amplifies [V feedback] by ~a factor of two and does not invert its phase; because it is fed to its non-inverting port.

4. Simultaneously, the input signal [Vin] is amplified by a factor of 1 and its phase inverted; because it it fed to the Op Amp's inverting port.

5. The overall consequence is the Op Amp subtracts [or differences] the non-inverted [V feedback] from the input signal [Vin]. It follows that the output signal of the Op Amp [same as input signal to UcD] was decreased in amplitude. Ditto for UcD's [Vout].

6. This prototype has a self-induced and increased overall negative feedback which is pronounced in the woofer region. Its impact on the inherent [and impressive] % THD and output impedance of UcD is unknown.

Best
Anton
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File Type: jpg UcD180LPbasscut.jpg (391.9 KB, 260 views)
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Old 19th April 2019, 05:53 PM   #42
satefan1973 is offline satefan1973  Netherlands
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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

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.
Congrats Bruno on a great achievement. Can you share the make/type of the mid woofer?

thanks,

Stefan
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Old 19th April 2019, 07:23 PM   #43
Windforce85 is offline Windforce85  Poland
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He obviously did not share it but he certainly will tell us more about it on High End Munich 2019 on Purifi Audio seminaries. We will get more to know also about his NCore refinement which is indeed much of refinement, as it boasts more loop gain especially in highest frequency range (or even supersonic) which is crucial from end-side performance. Of course, together with expected performance of 6.5-inch/15 mm-Xmax woofer.. I hope that he remembers about frequency modulation distortion along with this. Long-stroke midwoofers trying to reproduce good bass and good midrange together, always fail to sound right.
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Old 19th April 2019, 08:01 PM   #44
satefan1973 is offline satefan1973  Netherlands
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In my concept, i am not planning to use it for midrange at all. Hence, my interest for the large x-max.
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Old 19th April 2019, 08:05 PM   #45
Windforce85 is offline Windforce85  Poland
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This is reasonable but limits its practical implementations. I am curious how he will address it. Hope the depth and weight of this woofer will be reasonable to justify Sd decrease from say, 8-inch equivalent, possessing more relaxed stroke performance. I'm sorry for this off-topics.
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Old 20th April 2019, 11:17 AM   #46
satefan1973 is offline satefan1973  Netherlands
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Quote:
Originally Posted by satefan1973 View Post
In my concept, i am not planning to use it for midrange at all. Hence, my interest for the large x-max.
I realise is should specify this. Cross over (3rd order) is 1000hz.

Stefan
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Old 14th May 2019, 11:24 AM   #47
miero is offline miero  Czech Republic
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Info about new amplifier is available now: - 1ET400A - Purifi
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Old 14th May 2019, 11:32 AM   #48
spikestabber is offline spikestabber  Canada
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Hmm, my nc400 with its PSU just blew up after a working poweroff last night, good timing.
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Old 14th May 2019, 12:18 PM   #49
kokoriantz is offline kokoriantz  Lebanon
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Originally Posted by spikestabber View Post
Hmm, my nc400 with its PSU just blew up after a working poweroff last night, good timing.
How many hours did your amp function approximately in its life time ?
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