The yet tiniest single-sided LM3886? - Page 16 - diyAudio
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Old 10th July 2011, 08:14 PM   #151
hurtz is offline hurtz  Germany
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Ok, but they seem to be so similar there is no need for changes.

Back to topic so to speak, why is Ci (not Cin) bipolar anyway? The NS-schamtic says its to be a polarized capacitor, and looking through some other schematics, they don't use a bipolar cap there as well.

Puzzled cheers!
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Old 10th July 2011, 10:06 PM   #152
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The key to that is if the cap is large enough, and Fc is low, it's going to be a dead short at any reasonable audio frequency, so it won't have any voltage across it and polarity doesn't matter. I personally try to avoid using them whenever I can, but you have to be aware of all the problems that could arise if you don't.

Mike
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Old 10th July 2011, 10:47 PM   #153
hurtz is offline hurtz  Germany
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Thanks! :-)
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Old 11th July 2011, 01:10 PM   #154
Kay is offline Kay  Germany
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> Hi Kay. It might help if you elaborated.

look at #123

1. the most important thing are not the rails, but the ground
2. is a ground loop necessary?
3. the best way is using two bridges and connect ground only at the star ground on the power supply or nearby
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Old 11th July 2011, 02:26 PM   #155
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^ This loop won't matter, ground loops only effect sound upstream where the signal or speaker return happens, there is still a single point from PSU board to amp board possibility of connection to a star ground.
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Old 11th July 2011, 10:43 PM   #156
Kay is offline Kay  Germany
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maybe

if I do ground-routing,
I make it so short/low resistance as possible,
especially for high currents
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Old 12th July 2011, 01:09 AM   #157
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^ How would it be any shorter traces, unless using fewer capacitors or putting the PSU subcircuit on the amp board itself? You could combine the two ground traces but I would also aim for low resistance, by using wider traces as I mentioned previously but that can be done without any major layout changes.

This conversation has brought up another issue I'd overlooked. From what I remember, hurtz is designing the amp board for one LM3886 per board, which means there will need to be two amp boards for stereo use, two wires coming from both the positive, and the negative rails to handle both amp board but the PSU board connector appears to only allow for one wire connection per rail... so it would require one PSU board for every amp board as is.
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Old 12th July 2011, 04:20 AM   #158
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I feel compelled to repeat what I posted in #90, to be sure there is no potential for ground loops, you really should at minimum keep the high level and low level grounds totally separate. You might get away with combining the power and speaker grounds, but to use a single conductor for all grounds from the amp board to the power supply is inviting disaster. Even if you have a "star ground" on the amp board, you're still using one wire to connect it back to the power supply, combining low level and high level signals. I have the input, power and speaker grounds all on thier own conductors, never have any issues. Besides, like I said before, wire is cheap and it's easy to do it that way.

Mike
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Old 12th July 2011, 10:05 AM   #159
hurtz is offline hurtz  Germany
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As AndrewT/discrete explained some time ago, the RCRC-filter propertiesare actually worth keeping.
"Stereo" output-terminals have been added.
Star ground is now on the amp board itself, so only one common ground.
@Mike I know what you mean, but the trace-length between the AMP and the board is very short anyway, and then again I would wait for the test results to see how it goes.

Click the image to open in full size.

cheers!
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Old 15th July 2011, 03:14 PM   #160
hurtz is offline hurtz  Germany
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Hi folks,

I just got feedback from enzoR about the test results which are compared to the p2p pretty much the same. To directly quote the speaker-grounding issue: "Grounding the speaker - on the amp board or on the powersupply made hardly any difference."
There will be some more detailed test results when enzoR comes back I think.

For now I'd like to publish the final version of the amp or rather the release version 1.0.
Thank you all for your friendly support and most helpful explanations!

The official names are:

"no11 AMP" and "PSU+"

cheers!

DIYing is strongly encouraged, but please let me know how it went! If you are interested in buying a kit/assembled/PCB let me know as well!

A parts-list will follow!
Attached Files
File Type: pdf ampd.pcb.pdf (13.2 KB, 156 views)
File Type: pdf psu+.pcb.pdf (11.4 KB, 107 views)
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