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Old 30th November 2011, 11:30 AM   #31
marce is offline marce  United Kingdom
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Ther is a whole wealth of information regarding de-coupling on the web, it is a critical part of any electronic design these days, as there is more and more high frequency noise being created, both airborne and mains borne, never mind the digital devices and components in most peoples systems.
Such info as Analog Devices MT-101, first one I picked up on my desk.
For high frequency de-coupling it is the parasitic inductance that is the killer, so the smaller the route between pin and cap the better. Also small package X7R or COG MLCC caps (SMD 0603's 0402's) are best for this due to LOW parasitic inductance.
As to where do we draw the line, well the big 3 proffesional packages (Mentor, Zuken and Cadence) all now offer power delivery system integrity software.
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Old 30th November 2011, 06:47 PM   #32
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This was yatgai's topic, but in view of the feedback given
to my layout, I incorporated them and will post once more here,
with due apologies to the OP.

Click the image to open in full size.
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File Type: zip lm3886-r1.zip (59.9 KB, 78 views)
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Old 30th November 2011, 10:46 PM   #33
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Hi.
Would it not be good practise to take the speaker out 0 volt from directly inbetween C7 and C8. Im assuming that C5 and C6 also the 220pF across the input pins are to be soldered underneath the board. have a look at this link. From the menu select bypassing . Tutorials, Electronics made EASY, Williamson Labs
Regards
Ian
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Old 1st December 2011, 02:26 AM   #34
gootee is offline gootee  United States
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Pretty good work, so far! But those vertical resistors should be turned around so that the excess lead length is not connected to the chip pins.

And I would still want the input signal ground to run right next to the input signal trace(s), everywhere possible, removing the little board-ground stub from between them and right-angling one of them to be next to the other starting directly at the input connector, and putting stubs out to get to those electrolytic caps if necessary. The input traces are critical, since they are a low-level signal which will be amplified. Any geometric area between them will amount to more hum and RF in the input signal.

And I think I agree with all of what madtecchy said is needed, just above. Perhaps a jumper wire would be needed from an isolated output ground to between the two large caps. C5 and C6 could just be pushed a little closer to the pins, though. And the 220 pF should be pulled down to have its pads touch both input pins' pads. I have tried it with my PCB software and it can fit there.

Last edited by gootee; 1st December 2011 at 02:46 AM.
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Old 1st December 2011, 04:54 AM   #35
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Thanks! I'll make the suggested changes (as best as I can ).

Madtecchy - yes, I did plan to solder the bypass caps on
the copper side - can't get closer than that. I may just add pads
for SMD bypass caps too, for max flexibility.

I appreciate the suggestions and handholding towards
a good layout.
Anyone wanting the latest eagle files, pls PM me.
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Old 1st December 2011, 07:03 AM   #36
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Hi Quadtec.
I totaly agree with the S.M.D pads for the decoupling capacitors. Im guessing you will be building this amplifier very soon. Then you can start changing components im amazed by the diffrence components from diffrent manufacturers can influence the sound of these great sounding I.C's. Have fun there is much to be learned from building this type of amplifier and it will put you in good stead to take on more complex discrete Designs. Ps the link i posted was kindley given to me by gootee so thanks is due .Thankyou gootee
Kind Regards
ian
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Old 3rd December 2011, 07:21 PM   #37
gootee is offline gootee  United States
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According to my interpretation of Henry Ott, you will want to connect the four decoupling capacitors all to the load ground pin as directly as possible.

If you don't want to re-work the entire layout, you should consider adding a very thick short wire, from right behind the chip's load ground pin to a point near the ground end of C6. And if you do that, then I guess you might as well isolate the ground area containing the output ground pin and output ground connector from the rest of the board-ground copper.

P.S. Don't forget to also fill in all of the little gaps between pads and copper, and eliminate all of the acute angles in the copper, including pads-to-copper and copper-to-copper (no angles should be 90 degrees or less).
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Old 3rd December 2011, 08:37 PM   #38
gootee is offline gootee  United States
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Quote:
Originally Posted by gootee View Post
According to my interpretation of Henry Ott, you will want to connect the four decoupling capacitors all to the load ground pin as directly as possible.

If you don't want to re-work the entire layout, you should consider adding a very thick short wire, from right behind the chip's load ground pin to a point near the ground end of C6. And if you do that, then I guess you might as well isolate the ground area containing the output ground pin and output ground connector from the rest of the board-ground copper.

P.S. Don't forget to also fill in all of the little gaps between pads and copper, and eliminate all of the acute angles in the copper, including pads-to-copper and copper-to-copper (no angles should be 90 degrees or less).
(Note that madtecchy suggested the above, in post 33. Good call.)

I seems like C5 and C6 (the 0.1uF decoupling caps) should be able to go between the rows of chip pins, and connect the power pins almost directly to the output ground pin. They could probably just be soldered to the pins themselves, or maybe even just have their leads inserted into the same holes as the chip pins. But they should also be able to fit with their own pads, especially the really-small types that are available. The surface mount idea would work great too, of course.

It would probably be a good idea to also keep in place some 0.1uF caps where they are currently shown.

Last edited by gootee; 3rd December 2011 at 08:52 PM.
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Old 4th December 2011, 08:03 AM   #39
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by gootee View Post
It would probably be a good idea to also keep in place some 0.1uF caps where they are currently shown.
possibly rather than probably. One must check for resonance, if adopting two caps
__________________
regards Andrew T.
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Old 4th December 2011, 08:15 AM   #40
Mnvizb is offline Mnvizb  Lithuania
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I could recommend you a design I have built myself. It has probably no noise (cant hear any if sealed in metal box). CIRCUIT.lt : Elektronikos projektai The problem is that it is in Lithuanian. If you look in end of the article you can see that you can download pcb. Beware that pcb is mirrored (if you want unmirrored you should rotate so you can see CIRCUIT.LT). Just google translate it. If you need any help, PM me. Good luck!
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