LM3886 and active xover - how to draw groundplane? - diyAudio
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Old 27th November 2003, 07:01 AM   #1
AndersZ is offline AndersZ  Sweden
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Default LM3886 and active xover - how to draw groundplane?

Hi

I'm currently building active speaker modules for my open baffle dipoles (which have been computer eq/xover'ed until now). I plan to make one pcb for each channel (high, mid, sub, input) with the active components and an amp. Those four pcbs will be in the same box with the speaker. The xover/eq stage follows the same form as Linkwitz's Phoenix asp.

I'm not shure how to connect the groundpoint though, should I connect all the star points on the board to one and then draw it to the main point for the whole module or should I have the amp separated as long as possible?

All suggestions are welcome

Anders

(here's the in progress layout for the midchannel at the moment, with all the grounds separated and no connectors added)
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Old 27th November 2003, 09:25 PM   #2
moamps is offline moamps  Croatia
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separate star grounding signal and power grounds
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Old 28th November 2003, 05:49 AM   #3
AndersZ is offline AndersZ  Sweden
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thanks

/Anders
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Old 28th November 2003, 08:36 AM   #4
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Hi Anders,

what PCB layout program are you using? Do you have some absolute-beginners-tips for someone who is about to try to learn to make PCBs?


Goodluck,

Thijs
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Old 28th November 2003, 10:02 AM   #5
banana is offline banana  Hong Kong
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Default Some suggestions (long)

Are you going to make it a double sided PCB? You can use one layer entirely for ground plane, and then separate it as you desire.

I guess your PCB should have at least three grounds that would be connected to the outside. The audio input ground, the speaker output ground and the power supply ground. I suggest these three ground cables to be twisted with its' corresponding signal cable, i.e. audio input twisted with input gnd, spk out twisted with spk gnd, and pwr gnd twisted with V+ & V-.

About splitting the gnd plane on the PCB, my suggestion would be making three local gnd planes first. And then joint the three plane in single point. Connect those twisted cables close to its' destinated device, eg. input cable to Opamp input, spk cable to power amp output pin.

The chasis earth connection would be something tricky. Some say connecting it to input sockets, some say power supply. Better compare it for your own case.

Of course, it's my opinion only.

Click the image to open in full size.


some more pic
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Old 28th November 2003, 10:47 AM   #6
AndersZ is offline AndersZ  Sweden
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The plan is to use a single sided pcb with solid core wire where I have to cross copper on the pcb althpugh I guess I could make a double sided if I see the need.

Three ground planes connected seems like a good idea. I'll try that right after the weekend when I come home.

A question though: Do I have to earth the chassis? I haven't done so with my first try at a GC and it behaved very well.

Quote:
what PCB layout program are you using? Do you have some absolute-beginners-tips for someone who is about to try to learn to make PCBs?
I use Traxmaker in the Circuitmaker 2001. I don't use the auto placement features, instead I print the schematic (or show it on my second screen) and try to make the pcb design mimic the schematic. I belive I get a much more compact layout this way. When I think I'm finished I print it on regular paper for inspection and then it's time to print it on transpearancy, use the 150w halogene (?, don't know the word...) , process it, wash it, etch it and drill.

/Anders
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Old 28th November 2003, 11:43 AM   #7
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Thanks,

Goodluck with your project, and don't forget to send us some pictures

Regards,
Thijs
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Old 28th November 2003, 02:16 PM   #8
banana is offline banana  Hong Kong
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Quote:
A question though: Do I have to earth the chassis? I haven't done so with my first try at a GC and it behaved very well.
For safety reason, metal chasis must be earthed. For good shielding, chasis should be connected to circuit ground. But when more than one of your component is earthed, you get ground loop, or possibly hum. That's the contradiction, safety vs humming. I'm not confindent enough to leave my diy component un-earthed.

below is a good reading about grounding and hum.
grounding article
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Old 28th November 2003, 02:40 PM   #9
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Hi Anderz,

I decide to play a little with TRAXMAKER and I think I like it.

Thanks for the tips again. I made two small PCB for the a active-XO (I think very similar to Nelson Pass DIY active-XO). Could you tell me how I can get a graphic-file (jpeg, giff, bmp etc) from a traxmaker PCB file?

Kind regards,

Thijs
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Old 28th November 2003, 04:10 PM   #10
AndersZ is offline AndersZ  Sweden
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Quote:
Could you tell me how I can get a graphic-file (jpeg, giff, bmp etc) from a traxmaker PCB file?
By using a virtual printer program to capture the print.

Oh, and don't forget to mirror the copper layers when you're printing them.

Good luck

Anders
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