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Class D Switching Power Amplifiers and Power D/A conversion

Ultimate D class amplifier design in theory.... :)
Ultimate D class amplifier design in theory.... :)
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Old 12th August 2017, 11:43 PM   #1
Mikelandjelo is offline Mikelandjelo  Serbia
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Default Ultimate D class amplifier design in theory.... :)

So,this should be easy discussion.I know a lot about D class amplifiers....i built a lot of them.....so i am deeply infected with this .In my mind ultimate D class amplifier is something which has absolutely zero output noise without any signal on input,lowest possible distorsion,to be impossible to burn out,zero heat and it should have lowest possible quiescent curent....this last requires low switching frequency and lowest distorsion requires oposite......so whats the middle point solution?Whats minimum switching frequency that will give still perfect sound quality?I want to discuss full bridge and half bridge designs and not multi phase solutions.Any thoughts are welcome.
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Old 13th August 2017, 01:25 AM   #2
voltwide is offline voltwide  Ireland
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If you are really interested in the theory, you do not have to discuss but do the math. This is what Bruno Putzey did, with considerable succes.
So it would be a good idea to read his papers.
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Old 13th August 2017, 03:02 PM   #3
Mikelandjelo is offline Mikelandjelo  Serbia
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I am interested for discussion...i am doing math last 20 years.Did i miss something about ultimate amp characteristics?There are many DIY people here....maybe someone want to add something new or something i missed?
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Old 14th August 2017, 08:02 PM   #4
ChocoHolic is offline ChocoHolic  Germany
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Gotcha!
You are bored and hope to trigger an amusing battle of believes.
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Old 14th August 2017, 10:18 PM   #5
Bob Richards is offline Bob Richards  United States
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I just bought my first class D poweramp boards from Parts Express for a battery operated bluetooth boombox I'm building. I actually bought 3 different versions, and 2 of them had bad oscillation problems. The third board (TPA3116D) appears to work pretty well (no osc. and fairly clean transition into clipping).

My contribution here is the suggestion that ferrite beads and maybe even passive low pass filtering be used on the input, if there's any analog circuitry upstream (preamp, etc.). I don't know if there's any significant Rf energy at the input of a class D poweramp, but if there is, it could work it's way into the analog preamp circuitry in a way that could cause slewing related distortion products. If you're after the best possible sound, this could be a small issue.

As far as the switching frequency, it's all about the Nyquist frequency, where anything above half the switching frequency gets turned into a lower frequency. I'm sure you know what I'm talking about. You want to avoid having any aliasing distortion from that. How many dB down do you want the program material to be, when you get to the nyquist frequency? How low do you want the aliasing distortion to be? Personally I like high sample rates (maybe 500kHZ), so the anti-aliasing filter can pass 20kHZ no problem, and have plenty of room to roll off the signal very well before the nyquist frequency (250kHZ in this example). Reconstruction filters that are more than 2 pole can be tricky, and more load Z sensitive.

Another thing I do is to put a zobel across the speaker, so the rising impedance of most speaker drivers only goes so high (a 0.2uF in series with a 15 ohm 5W resistor for example), so the recontruction filter doesn't get mad, and generate high voltage transients.
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Old 20th August 2017, 11:59 PM   #6
Mikelandjelo is offline Mikelandjelo  Serbia
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Quote:
Originally Posted by ChocoHolic View Post
Gotcha!
You are bored and hope to trigger an amusing battle of believes.
Yup .... I am "infected" for a very long time.....I tried to achieve.....well its better to count what i didnt try .....And i would like one good discussion very much.I built something that i beleive is good.....but maybe i missed something....So,give it a try....Lets define some tests with scope,signal generator.....different loads etc. .....I would like to test what i have and maybe i missed something.Discussion cant hurt.My sample rate is 400Khz .... with BD modulation its 800Khz on output filter network.....and i have almost completely dead ,zero noise output without input signal...and with it ...Its not bad for start i think

Last edited by Mikelandjelo; 21st August 2017 at 12:03 AM.
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Old 24th August 2017, 07:02 PM   #7
Mikelandjelo is offline Mikelandjelo  Serbia
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Quote:
Originally Posted by Bob Richards View Post

My contribution here is the suggestion that ferrite beads and maybe even passive low pass filtering be used on the input, if there's any analog circuitry upstream (preamp, etc.). I don't know if there's any significant Rf energy at the input of a class D poweramp, but if there is, it could work it's way into the analog preamp circuitry in a way that could cause slewing related distortion products. If you're after the best possible sound, this could be a small issue.

Another thing I do is to put a zobel across the speaker, so the rising impedance of most speaker drivers only goes so high (a 0.2uF in series with a 15 ohm 5W resistor for example), so the recontruction filter doesn't get mad, and generate high voltage transients.
Ferrite beads on input cant do much work becouse they cant react with ultra small curent and here is voltage the issue ....voltage ripple.For me about this ....best working way is to have diferential input and BD modulated output stage...If all is properly designed output noise is absolute zero.Of course its not near close to be easy to figure out all instantly and make it to work..... Dont ask me how i know .

Zobel across the speaker or any impedance influence on speaker side is good idea....but if we make best possible working amplifier than we should have output impedance independant output stage/amplifier.Any thoughts about how this can be done?
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Old 25th August 2017, 06:38 PM   #8
Bob Richards is offline Bob Richards  United States
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Good point about the ferrite beads needing enough current to work. One of the tradeoffs with a switchmode amplifier is that in order to get the high efficiency, it has to work with ultra fast rise times, with come with Rf freq. spectra, so there's no way to have zero output noise, hence the reconstruction filter. Same story as with a DAC.

If you've got your circuit working as good as you say, then I'd concern myself more with durability with real world conditions. How good are the speakers protected in the event of amplifier failure? How well does it handle a rock guitarist blasting it well into clipping for hours? Does it clip with sharp corners or is there a circuit that keeps it from ever having sharp corners? What's the time constant of that circuit, or does it work in real-time? What about the turn-on (or turn-off) transient; is it safe to directly drive a delicate tweeter in a tri-amp'd system? Does it have a built in level indicator ready to drive external LEDs? How much humidity and ambient temperature range can it handle?
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Old 25th August 2017, 06:47 PM   #9
stocktrader200 is offline stocktrader200  Canada
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I have one I built that runs up to 2 Mhz at 42v rails. overload capacity drops off inversely with switching frequency. The sound quality is superb but mounted into a receiver , the FM was noisier that usual.
The other thing is that the overload is hard, if it is exceeded at all the amp will die.
A .47 ohm series output resistor cured the overload shutdown problem.
I do agree that Bruno's UCD design detailed on Phillips mosfet semiconductor sheets is a very good meeting of various comprimises
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Old 25th August 2017, 08:08 PM   #10
Mikelandjelo is offline Mikelandjelo  Serbia
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In my design .... on which i am still working ..... i do have almost dead zero noise output....or with other words i have less hum on output than with any AB class amplifier i had before...i compared Technics and Sharp amplifiers and few i have built which are ultra quiet.....And i figured out how to make absolute zero output noise output which will happen in next month (I am doing designing for living so time is issue a bit).

Speakers are buletproof protected as amplifier it self.Its impossible to couse any damage on amplifier in ANY type of overload.....it will not burn or even get warm if you make dead short on output,on each half bridge to ground,from + power rail to output or in case of overheating.......So speakers are protected very well i think.Hours of clipping are just fine (tested for 3 hours) becouse it will clip on very unique way and is capable to deliver flat top in that case BUT NOT as other amplifiers.I developed NEW PWM algorithm which keeps highest output quality and has higher efficiency than current solutions.Switching frequency and protection responce are NOT in relation to each other and on any switching frequency protection will have same responce.Sound quality i will not describe....i made it and i doubt that anyone will beleive that i will say the truth.....For me personaly this is something i never heard or saw better in my life.

Becouse i did few things VERY differently than anyone till now i achieved to have high definition sound when i have absolute switching phase match on output,which i never found that anyone made before in BD modulation.Every design with BD modulation requires small phase missmatch to work good and have clear output on low power output,but not mine.Also EMI and output noise ripple are very low ..... I have 5 to 10mV ripple and hf noise on output no matter is modulation up to clipping level or its no audio present on output.I cant say anything about humidity and ambient temperature range becouse i didnt test that at all.What i can say is that i dont have any heatsink , that i pulled up to 15A from amplifier without heatsink and its very stable ....There is small heat but nothing that needs heatsink to work.And i am using in prototyping phase IRFB5615 fets.....ringing is not present or its super small becouse of different output stage design.And i will claim one thing for sure.....You dont need eGAN fets to have clear switching.....they work better but they are not a must.Also story about D class is not finished yet nither is all discovered in this area.

Quote:
Originally Posted by Bob Richards View Post
One of the tradeoffs with a switchmode amplifier is that in order to get the high efficiency, it has to work with ultra fast rise times, with come with Rf freq. spectra, so there's no way to have zero output noise, hence the reconstruction filter. Same story as with a DAC.
It is possible to overcome this and have absolute zero output noise.If i did it someone else will do it for sure too.It took me years to figure out but is possible.

Last edited by Mikelandjelo; 25th August 2017 at 08:16 PM.
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