Effect of feedback in Class-D amplifiers - Page 2 - diyAudio
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Old 17th August 2005, 09:31 AM   #11
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I understand some of them are using a digital form of "room correction"? That's either got to be with a microphone or a voice coil...... lvdt?
They measure the response of the room-speaker combination by the use of a computer measurement program. This measurement is used to calculate coefficients for a FIR filter that are then loaded into the system. I.e. the room correction is done in the digital domain before the amp and it is capable of correcting frequency- and phase- response. It can be regarded as a sophisticated equaliser.

The result is not a cure-all but quite impressive.

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Charles
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Old 17th August 2005, 09:34 AM   #12
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.... and quite complex! So it is a microphone Great explanation of it thank you.

Seems it would be worth a listening experience? I won't be building one of those anytime soon.

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Chris
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Old 17th August 2005, 09:37 AM   #13
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I won't be building one of those anytime soon.
I won't do that either but I can definitely recommend a listen if you have the opportunity.

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Charles
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Old 18th August 2005, 06:20 AM   #14
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Hi Charles,

Thanks for the answer..

LM360 cost around at 15dollars each.. i have just recieved the samples from NSC..

But i want to refine my previous designs eliminating the level-shifters....going single supplies and H-bridge
New setup;
[LM6172]->LM319->XORS->IR2110->IRF250N
Simple and cost effective...
configured in Bridged mode in BD mode..switching in phase but audio signal out of phase thus improves damping and makes the output filter small...mean while also using common-mode inductor at output....
Thus it also helps in implementing 3 - Level PWM
Now one question, Since i am going to use bridge mode[BD-modulation] ... Do i require feedback...Since even order harmonics as well as bus pumping is eliminated , but then also there are odd order harmonics out there...

I myself want go open - loop....

What would be the wise solution.....

Sincere Regards,
K a n w a r
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Old 18th August 2005, 07:23 AM   #15
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Hi,

A quick look at the patent for what I think you're talking about will show you it's heavily dependant on feedback.

Maybe it's just me here but I take it for granted that open loop class d = "True Digital" with a boat load of correction circuits and tight local feedback loops. It would seem all too easy to be working backwards doing it that way, adding more circuitry, making it less efficient, reliable, etc.

Why don't you order one of those Mueta chips?

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Chris
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Old 18th August 2005, 07:27 AM   #16
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I'd prefer a solution with NFB as well.

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Charles
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Old 18th August 2005, 11:46 AM   #17
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Thanks once again, Charles.

So what are the advantages [more probably to say disadvantages in openloop] in your view about the implementation of NFB

sincere regards,
K a n w a r
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Old 18th August 2005, 02:22 PM   #18
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The advantages are the same ones as they are for conventional amps.

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Charles
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Old 19th August 2005, 10:07 AM   #19
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Ok Charles,
i would go for open-loop and should see what happens to the distortion figures, if they were not satisfying, then would go for NFB,then only..

Since i want to Drive 100V constant voltage line with frequency response from 30Hz to 15Khz only, thats why considering cost effective solution....

Secondly I also want to use complementary comparator scheme using dual comparators to obtain out of phase pulse signals...

Thanks for the help,
K a n w a r
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Old 19th August 2005, 05:19 PM   #20
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In theory a precise PWM modulator, a stable PSU (!) and a perfect switching stage would give a perfect amp even without any type of feedback.
I disagree. There are side-band components in basic PWM spectrum, very similar to phase modulated signal. The lower side-band reaches audio-band with significant level if switching freq/signal freq ratio is not enough.
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