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Old 26th March 2012, 12:38 PM   #1
Mfly is offline Mfly  Netherlands
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Default Active filter ground pour

Dear all,

I made a PCB design for an active subwoofer filter. It will be a 2 layer board. Because it has several potentiometers on the board edge, quite a few signal traces will end up in the ground layer.

In this situation would it be preferable to still use a single ground pour like this:

Bottom:
SubWooferFilter_PCB_1pour_Bottom.png

Top:
SubWooferFilter_PCB_1pour_Top.png

Or is it better to have ground pours in both layers like this:

Bottom:
SubWooferFilter_PCB_2pours_Bottom.png

Top:
SubWooferFilter_PCB_2pours_Top.png

Or doesn't it really matter in a situation like this (low frequency audio)?

Thank you for your input.

Cheers, Maarten
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Old 26th March 2012, 12:44 PM   #2
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I personally prefer to have such a big ground plane as can be done. I made several hand wrote PCBs and using soft like autotrax for DOS, and use large ground planes, for two reasons: less copper and acid waste, and quicklier acid attack, and electrically is also better.
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Old 26th March 2012, 01:38 PM   #3
marce is offline marce  United Kingdom
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Bothn layers withground pours and stiching vias between the two pours, to join them together at multiple points.
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Old 26th March 2012, 02:13 PM   #4
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Nice looking boards!
I do not use ground-planes in line-level based audio circuits. I prefer to keep the physical dimensions of the board to its minimum and pc traces as short as posasible with the maximum number of traces on the solder side. E
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Old 27th March 2012, 11:35 AM   #5
marce is offline marce  United Kingdom
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Ground planes for low level analogue do help keep noise down, I have seen them used on analogue designs for 27 years, and in't old days we wouldn't dreem of doing an analogue board without ground planes, pours.
The traces that are not power could be reduced in width a bit, they all look around 0.050".
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Old 27th March 2012, 02:41 PM   #6
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marce: I agree that ground planes should be used on low-level signals. I use them there and also on high-gain narrow filter circuits. This one seems to be line-level with a gentle filter. Poorly implemented ground planes can all to easily end up as antennae. E
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Old 27th March 2012, 08:51 PM   #7
marce is offline marce  United Kingdom
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Yes, it is important to add stiching vias to at least both ends of a long thin strip of a copper pour, often overlooked or missed. I put my vias in a different colour to the copper and step through the design, visually checking there are vias in the right places.
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Old 28th March 2012, 07:52 AM   #8
Mfly is offline Mfly  Netherlands
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Thank you all for your input. I'll go for the double ground pour then. Stitching vias shouldn't be a problem as the board will be manufactured by a PCB manufacturer and as such all ground connections will be plated through. I'll look into placing some extra via's on long thin stretches of copper to get a good connection between the two planes throughout the board.
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