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Crossover PCB in progress, ground plane or star/rail?
Crossover PCB in progress, ground plane or star/rail?
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Old 11th May 2019, 06:52 PM   #1
Lingwendil is offline Lingwendil  United States
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Default Crossover PCB in progress, ground plane or star/rail?

So, I haven't touched a solder iron for any audio projects in months, and wanted to put together a PCB design to hold me over. This is more-or-less the same as the ESP p09 crossover, but with the option of building the buffer opamp at the input as a shelving low-pass filter for baffle step correction. I oringinally decided on a ground plane, now I'm not so sure. I'm currently torn on which version to keep on working with. I modified the ground plane to have a central ground rail with a semi-star arrangement for the connections.

Anybody have an opinion? I feel like the ground plane idea is likely best, but some are adamant about using a star arrangement with such things. I have the ground plane connected only at the power GND terminal on the star/rail version, with it throughout the board as a sheild only. I can easily delete the sheild and use only the star/rail too.

Yes, I will be posting design files once done
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File Type: png qcmDdkk9cnc.png (176.9 KB, 256 views)
File Type: png startop.png (220.3 KB, 256 views)
File Type: png star bottom.png (184.7 KB, 253 views)
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Last edited by Lingwendil; 11th May 2019 at 06:55 PM.
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Old 11th May 2019, 07:02 PM   #2
ohdsp is offline ohdsp
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Here are my thoughts for what it's worth. From an EMC perspective ground planes are nearly always better. With a good PCB layout the ground current will still flow where you want; without any need for star connections or separated grounds.

However on both version of your PCBs if you form a ground loop, as the input and outputs are on opposite sides of the PCB, then that ground loop current will be flowing through the ground nodes of the filter circuits.

My understanding is that it is better to have the inputs and output grounds next to each other, so swap the locations of power and input, so any ground loop currents are away from the filter circuit. Unless you then connect the power supply to earth as well, guess you would want them all at one end of the PCB then.
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Last edited by ohdsp; 11th May 2019 at 07:08 PM.
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Old 11th May 2019, 07:09 PM   #3
MarcelvdG is offline MarcelvdG  Netherlands
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I'm in favor of using ground planes whenever there is no good reason not to do so. They help to keep loop areas small, reducing pick-up of any RF fields that may be around.

(If you would have included a power supply, I would advise you to keep the return paths of the smoothing capacitors separate from the ground plane, but it looks like the electrolytics are just for decoupling.)
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Old 11th May 2019, 07:15 PM   #4
Lingwendil is offline Lingwendil  United States
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Hmmm.

So, following what you're saying- I'll swap the input buffer circuitry to the right side of the board, and then that'll keep the power stuff all on the opposite end from the input/output connections. I'll just need to bring the input traces back the other way, but it makes much more sense to keep it all signal on the one side, power on the other. Thanks!
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Old 11th May 2019, 09:04 PM   #5
Lingwendil is offline Lingwendil  United States
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Alright, changed it up a bit, and opened up the ground some-
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File Type: png 31tx9Pjq9d2.png (166.7 KB, 71 views)
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Old 13th May 2019, 10:54 PM   #6
Mark Whitney is offline Mark Whitney  Netherlands
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Here is my work in progress.
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File Type: png filter.png (66.3 KB, 95 views)
File Type: png filter1.png (52.4 KB, 92 views)
File Type: png filter2.png (59.3 KB, 73 views)
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Old 14th May 2019, 01:07 PM   #7
Lingwendil is offline Lingwendil  United States
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Nice tight layout
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Old 14th May 2019, 03:02 PM   #8
s3tup is offline s3tup
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Rules i set to myself:
1. Always star ground.
2. Put all i/o connectors in same place
3. Never separate power rails, put power supply closest to the heaviest load.
4. Remove the star ground and put solid plane. Cut planes if you have to. If everything is right, no cuts needed.
5. Filter everything going in and out. Ferrite/ceramic caps/CM chokes/T-filters on PS, T-filters/CM chokes on analog. CM are not always necessary/good.

These analog low-power devices might benefit from heavy local bypassing (extremely low esr solid caps + np0/pps + series R to main regulator).

Print the pcb, take a pen and draw supply and return circles/currents for PS and analog signals.
They should not intersect kinda strict, but well...
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Last edited by s3tup; 14th May 2019 at 03:06 PM.
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Old 14th May 2019, 05:57 PM   #9
Mark Tillotson is offline Mark Tillotson
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One fact its worth knowing about groundplanes in standard 1oz copper pcb is the resistance per-square is about 0.5milliohm, ie 0.0005 ohms. 10mA flowing between two arbitrary places on a large ground plane is going generate something in the order of 5 or 10ÁV. If the signal level is about 1V, that's -100dB down. Something like an active crossover or line preamp isn't going to be troubled by this. A microphone or phono preamp is a different matter.
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Old 14th May 2019, 09:03 PM   #10
Lingwendil is offline Lingwendil  United States
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Here we go, still working on it but the power traces are the part I'm having the most fuss with, I may be just about done with it though.

I've embraced the ground plane
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File Type: png 568tLdJ3N6C.png (149.2 KB, 45 views)
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