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Old 24th May 2006, 01:06 PM   #1
knabsol is offline knabsol  Sweden
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Default Carlos AD815 preamp PCB

Hi guys!
I´m playing around a little in eagle and I´m almost finished with the AD815 preamp by CarlosFM.
But I just want to get some thoughts about the layout. Should I have a groungplance as I have now?
There are some things I know about, such as mounting holes and that it´ll be a bit tricky to solder some hole mounted components on the smd side. But that´s ok for me.
So..what´s good and bad?
/Christopher
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Old 24th May 2006, 01:11 PM   #2
knabsol is offline knabsol  Sweden
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Old 24th May 2006, 01:19 PM   #3
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My first impressions of the PCB are #1 make the heatsink area larger.
#2 definately scrap the groundplane (or make it as small as possible). And #3 put some decoupling caps on the supply lines close to the pins. I believe that they advise against using a groundplane somewhere in the datasheet, I could be wrong it's been a while since I looked at it.

As far as soldering hole mounted components on the SMD side...why dont you just put them on the other side of the board????

Best of luck with the design.
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Old 24th May 2006, 01:34 PM   #4
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I think it will be just fine but I'll advise you to have groundplane on both sides. Reconsider also how high supply voltage you will need, higher = hotter IC.

You haven't thought of TPA6120 which consumes a lot less and is faster? Both IC's are current feedback.

A small thing about your pcb: Why don't you adjust the input a bit so you won't get holes in the groundplane?

You have forgot decoupling of the supply voltage, extremly important!

Notice also (as Jocko Homo pointed out) that the amps aren't identical. One more reason to look at TPA6120

Notice also the inout bias current of 10-90 uA!!!! This will/can can create heavy offset which might not create any trouble since you have an output coupling cap.

You could take a peek at my TPA6120 project.

Check how I have done the double groundplane.

Click the image to open in full size.

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Old 26th May 2006, 10:35 AM   #5
knabsol is offline knabsol  Sweden
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Thanks for your help, I Will apply these adn see what I come up with. And I´ll also have a look on your project Per-Anders, looks interesting!

I have one little question, what are the pros and cons with a groundplane and a star ground? I understand it´s different wheter you´re designing a HF circuit like a switching supply or RF circuits than audio electronics. Is there any general rule for how you should design audio circuits?
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Old 26th May 2006, 10:42 AM   #6
knabsol is offline knabsol  Sweden
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Or should I just make it double-sided and use the bottom layer as a groundplane?
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Old 26th May 2006, 12:21 PM   #7
knabsol is offline knabsol  Sweden
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Sorry for all posts but now I´ve read the datasheet morecarefully and asked some people here and decided to go with a ground star and double sided pcb.
So here´s the new result. Better?
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Old 26th May 2006, 12:23 PM   #8
knabsol is offline knabsol  Sweden
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Old 26th May 2006, 01:50 PM   #9
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Quote:
Originally posted by knabsol
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Very nice...now just shorten up the feedback loop and you're done!
I would keep the traces as short as reasonably possible for this, especially since this is a high speed device....feel free to correct me if I am wrong about this.

Also what are you planing to do about nulling the ofset? Are you using the regulator as Carlos did, or a servo of some kind?

G.
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Old 26th May 2006, 02:14 PM   #10
knabsol is offline knabsol  Sweden
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Thank you very much Gcollier!
So is this somewhat what you mean by shorting the feedback? I used smd resistors there instead. Better?


I have planned to try carlos nulling circuit or maybe with none at all. that´s why I got the jumper there so i can take it away without resoldering anything.
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