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Old 8th June 2005, 03:24 PM   #31
LBHajdu is offline LBHajdu  United States
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I donít understand much about class-d, thatís probably why I see them as similar.
I just see a comparator, inverter, and gate driver.

Do you think your amp will perform better then the IRF reference?

I certainly agree that short connections are better at these high frequencies. Iím just saying the SOIC package I think I can solder, However the SSOP (the inverter of the IFR amp) dose not look possible. Thatís why at least your use of a different type of inverter looks like a big benefit to me.

Oddly enough I canít get my hands on any triple inverters in the 8-SOIC package, but if your works better it may not be a problem.

Leve
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Old 8th June 2005, 03:51 PM   #32
SSassen is offline SSassen  Netherlands
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LBHadju,

The IRF design is a classic hysteretic self oscillator with pre filter feedback, my design uses the SODFA concept, because I realize the difference isn't quite clear allow me to illustrate both concepts below and point out the differences:

Hysteric self oscillator:

Click the image to open in full size.

As is evident from the above image the integrator gets its feedback before the low-pass filter of the amp. In essence this is a sigma-delta modulater, indentical to the concept used in sigma-delta D/A convertors.

SODFA self oscillator:

Click the image to open in full size.

In the above image you can clearly see the difference, there's also feedback at the comparator input. Due to this feedback the amp is less prone to be affected by fluctuations in the supply lines, up to 20dB better than the hysteric self oscillator.

Obviously there's a lot more going on, but that's the gist of the matter. Overall the SODFA concept is a good one for a sub-amp as obviously the supply lines will be heavily taxed due to the high currents resulting from driving a large woofer at low frequencies.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
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Old 8th June 2005, 03:59 PM   #33
SSassen is offline SSassen  Netherlands
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Oh, and the invertor used in the IRF design is just a simple 7404, it is available in quite a number of different packages, including DIL14 and smd of course. If you ask me I think the use of digital logic ICs in their design is one of the design flaws, as is the way they do level shifting and there's a few other flaws as well. This does make the IRF reference design look more like a high-school project to me, rather than something you'd expect from a respectable manufacturer such as IR, but that's just my opinion really.

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Sander Sassen
http://www.hardwareanalysis.com
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Old 8th June 2005, 05:15 PM   #34
subwo1 is offline subwo1  United States
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Thanks for giving the comparison of the hysteric and the SODFA methods. Also, I think the choice to use a sealed enclosure is commendable. With its smoother response, it gives more natural sound IMHO.
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Old 10th June 2005, 12:36 PM   #35
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@ Sander

Fairly you had add the source of your abowe images !

http://hifiakademie.de/.?id=0&si=MTE...C4xNzkuMTE4fCA
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Old 10th June 2005, 12:42 PM   #36
SSassen is offline SSassen  Netherlands
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Lenz,

I grabbed them from another forum, hifi-forum.de, as they contained no copyright notice I presumed they could be used freely. If they're yours then I apologize but cannot edit the post as it is closed after 30-mins.

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Sander Sassen
http://www.hardwareanalysis.com
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Old 10th June 2005, 03:23 PM   #37
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http://rocky.digikey.com/WebLib/Line...ata/LT1016.pdf
See Page 2:

Are comparator pins 8 and 5 reversed in your drawing?


-=Randy
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Old 10th June 2005, 03:52 PM   #38
SSassen is offline SSassen  Netherlands
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Thanks Randy,

You're absolutely right. I've just checked the datasheet against the library for the LT1016 in my cad design software and it indeed has pins 5 and 8 swapped. I've made a new library that has the correct pinout. The below schematic is the correct one.

class_d_amp_005
http://hardwareanalysis.com/images/a...arge/11527.gif

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Sander Sassen
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Old 10th June 2005, 08:45 PM   #39
LBHajdu is offline LBHajdu  United States
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Thank you for the explanation and drawings it makes it clear for us guys that are new to these concepts to keep up. I have some more questions if you donít mind answering them.

Will your amp be usable full range?

Do you dislike the inverter in the IRF board, because it cause as time delay between the two connections going to the gate driver or is there another reason?

Would it be possible to use 2 optocouplers as the inverter/level shifter or are they to slow and / or require too much current? I can draw you an example of what I mean if you wish.
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Old 11th June 2005, 01:16 AM   #40
SSassen is offline SSassen  Netherlands
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LBHadju,

Opto couplers could work yes, but I'm trying to build something that'll match, or surpass, other class A/B and class-D amps and is also applicable full range. Optocouplers really don't belong in a design such as this, they're perfectly useable if this was a switch mode power supply, or a bucket convertor, or better yet; a motor driver. Besides the current solution with the two transistors is both elegant, simple and very fast, optocouplers would not offer a better solution in this case.

They might be if I was operating the driver stage at very high voltages and would like to keep the other electronics out of harms way in case of a shortcircuit of a failure in the output stage. In that case we quickly move into the realm of above mentioned SMPS or car-audio or PA use.

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Sander Sassen
http://www.hardwareanalysis.com
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