Lm3886 PCB design - diyAudio
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Old 16th August 2014, 04:26 PM   #1
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Default Lm3886 PCB design

Hello all,

I've been looking for a well designed PCB layout for the lm3886. I haven't downloaded any software to design my own as I'm just starting out and just want to see if my basic method for creating the pcb works before I go any farther with the process. I don't have a laser printer or any other fancy devices to create one so I plan on drawing the layout with a waterproof marker, use some etching solution, and then use nail polish remover to finish the job.

Here's a layout that I think I want to try, however, I don't see a mute switch included, unless I have overlooked it. Any input or other pcb layout would be greatly appreciated.
Click the image to open in full size.
http://diygainclone.blogspot.com/201...er-supply.html

Last edited by chasebank; 18th August 2014 at 12:07 AM. Reason: image fix
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Old 17th August 2014, 09:33 AM   #2
AndrewT is offline AndrewT  Scotland
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I can't see your attachment.

All the wiring coming to your chipamp must arrive as twisted pairs or twisted triplets.
The traces that carry these currents to the chip MUST maintain close coupling.
i.e. the signal input from the twisted pair to the +IN and -IN pins must remain VERY CLOSE together to minimise LOOP AREA.
This must include the few components forming the two input filters.

The Power triplet of -ve, PG and +ve must remain close coupled from the twisted triplet all the way to the to +ve pins and the -ve pin.
The Cs MUST stay close to the -ve and +ve pins and connect to the third trace of the close coupled triplet.

etc .....
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Last edited by AndrewT; 17th August 2014 at 09:39 AM.
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Old 18th August 2014, 12:15 AM   #3
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Quote:
Originally Posted by AndrewT View Post
I can't see your attachment.

All the wiring coming to your chipamp must arrive as twisted pairs or twisted triplets.
The traces that carry these currents to the chip MUST maintain close coupling.
i.e. the signal input from the twisted pair to the +IN and -IN pins must remain VERY CLOSE together to minimise LOOP AREA.
This must include the few components forming the two input filters.

The Power triplet of -ve, PG and +ve must remain close coupled from the twisted triplet all the way to the to +ve pins and the -ve pin.
The Cs MUST stay close to the -ve and +ve pins and connect to the third trace of the close coupled triplet.

etc .....
Not sure what's up with the image but I'll just include the link. I took this layout and adjusted the pin 8 area so I could connect a mute switch. However, the simple method used that is mentioned in my first post failed. I ordered a powdered ferric acid and after mixing it with water it heated up quite well. So I proceeded to add my hand drawn pcb into the hot etching solution and it basically stripped everything off instantly....
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Old 18th August 2014, 07:45 AM   #4
AndrewT is offline AndrewT  Scotland
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my description:
A complete mess.


Attach your pics.
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Old 18th August 2014, 03:50 PM   #5
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Well it melted away so I don't have any pics. But It looks pretty much like the schematic in the blog link I added in first post.
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Old 18th August 2014, 04:13 PM   #6
Mihkus is online now Mihkus  Estonia
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Supply rails should be very close to eachother.. On double sided design Vee on one side and Vcc on the other with 1,6mm or less spacing between them. Theres a nice field between them. There are so many designs out there and checking each one is time quite consuming.
But it can teach you the basics of analog PCB design. Id rather start from reading books...
It will save you alot time.

Also the design you posted has one missing part, 220pF capacitor between +input and -input. Without it the chip can start to smoke...
Not when speaker isnt connected.

Last edited by Mihkus; 18th August 2014 at 04:19 PM.
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Old 18th August 2014, 04:21 PM   #7
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Quote:
Originally Posted by Mihkus View Post
Supply rails should be very close to eachother.. On double sided design Vee on one side and Vcc on the other with 1,6mm or less spacing between them. Theres a nice field between them. There are so many designs out there and checking each one is time quite consuming.
But it can teach you the basics of analog PCB design. Id rather start from reading books...
It will save you alot time.
They should be or shouldn't be close? Some designs keep them close and others I've see separate them on opposite sides of the board. I probably wont be able to make my own pcb and have to use one of the proto boards.
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Old 18th August 2014, 04:26 PM   #8
Mihkus is online now Mihkus  Estonia
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Only idiots keep them far away from eachother. Theres electrical field between them

Last edited by Mihkus; 18th August 2014 at 04:37 PM.
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Old 18th August 2014, 04:58 PM   #9
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Quote:
Originally Posted by Mihkus View Post
Supply rails should be very close to eachother.. On double sided design Vee on one side and Vcc on the other with 1,6mm or less spacing between them. Theres a nice field between them. There are so many designs out there and checking each one is time quite consuming.
But it can teach you the basics of analog PCB design. Id rather start from reading books...
It will save you alot time.

Also the design you posted has one missing part, 220pF capacitor between +input and -input. Without it the chip can start to smoke...
Not when speaker isnt connected.
I don't see that on the data sheet, but have noticed it on an updated
schematic.
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Old 18th August 2014, 07:06 PM   #10
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Check diodes on PSU.
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