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Class D Switching Power Amplifiers and Power D/A conversion

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Old 19th October 2012, 02:00 PM   #1
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Default Exploring class D improvements ideas.

For historical reason, badly designed amps for low cost consumer or PA class D amps has bad reputation near some sectarian audiophiles. But lot of us knows how good they can measure and sound. up to the highest level of quality.
And it is the future, waiting for direct digital conversion/amplification.

So, let-us use this thread to explore all together, on a theoretical as well as practical point of view all the ideas we can imagine in order to improve further this class of amps.
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Old 19th October 2012, 02:21 PM   #2
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My first contribution to this thread can be resumed on two ideas.

First, some report a "clinical" sound to the pulse-width modulation used in Class D, same remark they had about the first historical DA converters.
This is due i believe, to the limitation of the analyze capability of the ultra low levels.
So, we can imagine to add in serial with the switching power transistor of a class D amp, a class A transistor, with an analog modulation at low level.

The second idea is to fight against the switching frequency problems.
There is a technological limitation to the switching frequency due to the speed of the available power fets. Those speed will increase with technological progress, but we are stuck with what we can buy.
I do not enter in the details of efficiency and distortion compromise we are obliged to do, in order to optimize the switching frequency. You know that, higher is this frequency, easier is its filtration before we send an analog signal to our beloved loudspeakers.
My idea is very simple. Using two D amps, in bridge configuration (phase opposition) with a common clock, and a quarter of wave delay for one of the amps of the bridge.
it will act like a X2 oversampling method, and, in a way, double the switching frequency.

Waiting for your comments and ideas, with apologizes for my poor English..
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Old 19th October 2012, 03:52 PM   #3
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This already exists, check out the Crown BCA amplifier, it runs a 250kHz carrier, but the three level modulation "balanced current amplification" scheme boosts the frequency to 1MHz, according to Crown in their BCA manual.

The "filterless" class d is another example, like the BCA, it also uses three level modulation which doubles the frequency at the output.
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Old 19th October 2012, 04:19 PM   #4
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Quote:
Originally Posted by Tekko View Post
This already exists
I'm sure, and never pretend any idea i can have as original.
I wonder who can have a totally brand new idea in electronic nowadays, see what i mean ?
My second idea seams not genuine, as well: Home

All that do not impeach-us to evaluate, comment, test.
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Old 19th October 2012, 05:00 PM   #5
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So what is the reason these two technologies are reserved for high power PA and/or low power such at portable devices ?

PRICE! It would simply cost too much, noone would wanna buy these products. Also it uses twice the amount of components per channel as the commonly used halfbridge designs found in comsumer audio today.

I believe hypex has the cheapest bridgemode class d on the market and quite possible the best sounding as well, but do ppl buy them ? NO! they opt for something cheap made in china, nowdays sound quality is not as big of a concern as price, ppl rather buy a cheaper product than spend big money to get good sound.
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Old 19th October 2012, 05:32 PM   #6
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Originally Posted by Tekko View Post
So what is the reason these two technologies are reserved for high power PA and/or low power such at portable devices ?PRICE!
Not realty our concern, here.
Means we are supposed to focus our interest in quality for money, and class D amps are very promised in this matter.
I believe there is some interest if the members of this forum can share their experiences, expertises and ideas in exploring the class D amps (the younger continent) in order to improve-it to the top. Hoping that it will lead to real community DIY projects
Is that was a bad idea ?
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Old 19th October 2012, 05:46 PM   #7
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Component count is another factor, instead of using fullbridge and three level modulation that emulates a doubled switching frequency, a haldfridge is used whith a raised switching frequency, just look at fumac (huygens audio) which pushes his class d amplifiers up to 2MHz switching frequency.
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Old 19th October 2012, 09:10 PM   #8
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Sorry Christophe, I cannot contribute to class D, I have never even listened to class D other than my cellphone. My comments on SSA for a digital amplifier was purely speculative.
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Old 19th October 2012, 09:46 PM   #9
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Originally Posted by Nico Ras View Post
I have never even listened to class D
Nico, may-be time to loose your virginity ?
I'm pretty sure that L.C. will join this thread very soon after his listening session in the studio where his SSA operate.
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Last edited by Esperado; 19th October 2012 at 09:49 PM.
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Old 19th October 2012, 10:04 PM   #10
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Originally Posted by Esperado View Post
Nico, may-be time to loose your virginity ?
I'm pretty sure that L.C. will join this thread very soon after his listening session in the studio where his SSA operate.
Christophe,

Talking about virginity, it has disappeared between the folds of my stomach and I sometimes spend the whole morning finding it to urinate. Sometimes I give up finding it and then people just think of me as a sweaty old man. So before I can lose it I must find it - is this very important,

Jokes aside, I would very much want to take a stab at a well designed class D amp, I do understand the concept and at times wondered if one cannot make the controller chip using a little 18F6240 Pic, I does have some good features such as 40MHz clock and many in built peripherals.
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