PCB Mistakes/Optimization(?) - Page 2

OmarAvelar · 5th April 2007, 04:19 PM

The PCB machine at campus doesnt have all the milling tools, so I need to stick with some design stuff like separation and spacing, plus I am still learning

. Thanks though.

How does this look?

BWRX · 5th April 2007, 04:49 PM

Why does everyone always leave off the speaker ground? That needs to be connected very close to the power supply ground, preferably between the supply caps.

Power supply and ground lines should be as thick as you can make them since they will carry higher current.

jaycee's layout is pretty good. Move the V- through hole over and add a speaker ground and it would be even better

jaycee · 5th April 2007, 07:56 PM

Why move the -V ? There is plenty of clearance. It might not look it on the picture because it's only a low res picture. At 600DPI (which i generate my laser transfers with) it is fine.

The speaker ground is best returned to the power supply ground. On my board, the capacitors on that board are local decoupling only. There is a seperate board containing 4x4700uF capacitors, 2 per rail. The speaker ground connects to the main ground point there.

edit: I've noticed so many people try to use EAGLE in a really strange manner. The idea is, you create a schematic and THEN lay a board out from that. EAGLE will then guide you to make sure you get connections correct. I don't get why people just try to use the board layout part by hand.

Undoubtedly one of the reasons is EAGLE not having parts in its library. In my opinion, learning to create parts is important, and it's also pretty easy. Admittedly, it took me a good 3-4 months and many attempts at designing PCB's before I got good enough to produce a layout like my chipamp.

mr.duck · 6th April 2007, 10:57 AM

Quote:

Originally posted by markiemrboo
You also seem to be missing the 4.7uF input capacitor. It is not strictly necessary, but if the input has any DC it should remove / significantly reduce this. DC at the input will get amplified and end up as much larger DC at the output. To an extent, DC at the output is "A Bad Thing".

I was wondering how effective the 22uF cap in the feedback loop is at reducing DC coming from the source?

I'm more familiar with DC servos that can completely zero the offset and keep the hole thing DC coupled

pinkmouse · 6th April 2007, 12:47 PM

Quote:

Originally posted by jaycee
In my opinion, learning to create parts is important, and it's also pretty easy.

I couldn't agree more.

BWRX · 6th April 2007, 03:42 PM

Quote:

Originally posted by BWRX
Move the V- through hole over and add a speaker ground and it would be even better

Quote:

Originally posted by jaycee
Why move the -V ? There is plenty of clearance.

Hi jaycee. I didn't mean move the V- through hole because of clearance issues. See that attached picture for an idea of what I meant. I would also move C6 to the left and C4 to the right so their pads are more in line with the traces. That will allow you to make the ground pour a little larger as well.

jaycee · 6th April 2007, 09:58 PM

Ah, i see what you mean now

Well, I explained already why speaker ground doesnt return to that PCB I guess....

I did think about it so that a zobel could be put on the board... but I have found that the zobel works just great across the speaker terminals... indeed I've run the board with no zobels at all and not had any stability issue.

I might be tempted to make Gerbers available

BWRX · 7th April 2007, 12:45 AM

The speaker ground really should return to the center of the caps closest to the chip because they supply the current for most transient demands. Plus, it makes the wiring a bit tidier.

jaycee · 7th April 2007, 08:02 AM

These caps are small.. 330uF in my own amp. They're there for local decoupling only. The high current flows in the capacitor bank PCB, so the ground return is best taken there.

I'm used to making discrete amps and that's the way it's done there also. I simply made this dual LM3886 board because I wanted something quick, cheap and easy.

fallow · 10th April 2007, 11:01 AM

Hi,

Just one comment for PCB design:
try to avoin sharp corners and shapes (90 dergees corners).

That is to reduce the (if I recall right correct me if I'm totally wrong) circular flow of current, which will affect to noise of the wire.

And use as thick wires as possible, at least in wires in which the current is high.

5th April 2007, 04:49 PM	#12
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	Why does everyone always leave off the speaker ground? That needs to be connected very close to the power supply ground, preferably between the supply caps. Power supply and ground lines should be as thick as you can make them since they will carry higher current. jaycee's layout is pretty good. Move the V- through hole over and add a speaker ground and it would be even better __________________ Brian

7th April 2007, 12:45 AM	#18
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	The speaker ground really should return to the center of the caps closest to the chip because they supply the current for most transient demands. Plus, it makes the wiring a bit tidier. __________________ Brian

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5th April 2007, 04:19 PM	#11
OmarAvelar diyAudio Member Join Date: Apr 2007	The PCB machine at campus doesnt have all the milling tools, so I need to stick with some design stuff like separation and spacing, plus I am still learning . Thanks though. How does this look?

5th April 2007, 07:56 PM	#13
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Why move the -V ? There is plenty of clearance. It might not look it on the picture because it's only a low res picture. At 600DPI (which i generate my laser transfers with) it is fine. The speaker ground is best returned to the power supply ground. On my board, the capacitors on that board are local decoupling only. There is a seperate board containing 4x4700uF capacitors, 2 per rail. The speaker ground connects to the main ground point there. edit: I've noticed so many people try to use EAGLE in a really strange manner. The idea is, you create a schematic and THEN lay a board out from that. EAGLE will then guide you to make sure you get connections correct. I don't get why people just try to use the board layout part by hand. Undoubtedly one of the reasons is EAGLE not having parts in its library. In my opinion, learning to create parts is important, and it's also pretty easy. Admittedly, it took me a good 3-4 months and many attempts at designing PCB's before I got good enough to produce a layout like my chipamp.

6th April 2007, 09:58 PM	#17
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Ah, i see what you mean now Well, I explained already why speaker ground doesnt return to that PCB I guess.... I did think about it so that a zobel could be put on the board... but I have found that the zobel works just great across the speaker terminals... indeed I've run the board with no zobels at all and not had any stability issue. I might be tempted to make Gerbers available

7th April 2007, 08:02 AM	#19
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	These caps are small.. 330uF in my own amp. They're there for local decoupling only. The high current flows in the capacitor bank PCB, so the ground return is best taken there. I'm used to making discrete amps and that's the way it's done there also. I simply made this dual LM3886 board because I wanted something quick, cheap and easy.

10th April 2007, 11:01 AM	#20
fallow diyAudio Member Join Date: Nov 2004 Location: Tampere	Hi, Just one comment for PCB design: try to avoin sharp corners and shapes (90 dergees corners). That is to reduce the (if I recall right correct me if I'm totally wrong) circular flow of current, which will affect to noise of the wire. And use as thick wires as possible, at least in wires in which the current is high.

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