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Class D Switching Power Amplifiers and Power D/A conversion

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Old 13th October 2007, 11:08 AM   #11
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Dithering is the intentional addition of noise inside the loop in order to decorrelate modulator noise patterns (so called limit-cycles) that may lead to "tones".

Regards

Charles
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Old 13th October 2007, 10:15 PM   #12
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I managed to kill the noise so all that is left now is small artifacts on some frequencies and a faint hum.
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Old 14th October 2007, 04:31 PM   #13
fredos is offline fredos  Canada
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Why did you try to run it at 8 mhz? You will never be able to drive power stage at that frequency...I already use this topology in my HVI serie amplifier, but take low frequency feedback at the output and hight frequency feedback before the coil...Work very weel at 500 Khz...

Fredos
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Old 14th October 2007, 04:38 PM   #14
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Hey fredos!

Well the 8MHz xtal module was all i had, i also had a 2MHz xtal module but that one was broken, no output.

Yes i know i cannot run a real output stage at these frequencies, but i can use another 74HC74 to lower the frequency of the master clock to a lower frequency.
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Old 19th October 2007, 02:23 PM   #15
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Heres a schemo of a new design iŽve whipped together.

http://diymania.hv4all.com/selfosc%20classd/D-Amp2.png <-- will it work with the level shifters and that stuff ?
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Old 19th October 2007, 02:28 PM   #16
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Why do you use a TL 082 as a sluggish comparator instead of feeding to integrator output to the first schmitt-trigger ?

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Charles
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Old 19th October 2007, 03:01 PM   #17
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Good question! Never thought of that really.

Tried it now on my simple prototype and it works!!

IŽll go ahead and cad the board.
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Old 19th October 2007, 03:07 PM   #18
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OK at least you understood what I meant to say. For those who didn't the above sentence should read: "....... instead of feeding THE integrator output to ........"

Congrats on your working test setup.

Regards

Charles
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Old 19th October 2007, 03:08 PM   #19
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Edit: by removing the comparator, THD shot shyhigh, from 0.07% with the comparator, to 8% without the comparator.
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Old 19th October 2007, 03:42 PM   #20
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Maybe your switching frequency is now way off - which you could set by changing the integrator cap.
What ground are the Schmitt-triggers referenced to ?

Regards

Charles
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