lm3886 linkwitz board + ?'s on Eagle - diyAudio
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Old 15th February 2006, 08:07 AM   #1
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Cool lm3886 linkwitz board + ?'s on Eagle

So I made my first board for linkwitz's lm3886 design. Being the poor guy I am, Im trying to fit 4 amps on one of the small 2.5 x 3.8 boards you can get at pcbexpress (the 3 for 51 deal).

BTW, pins 2, 6, and 11 will be completely chopped off.
Pin 5 will be halfway just so that I can bridge 1 and 5 w/ a jumper.
The 9 to 10 cap will be soldered in underneath.
The feedback res/cap will be soldered on top on the 3886.
Only half of the pcb board is shown with only 1 amp.
What do ya think?


My ?'s:
How do I copy this whole circuit so that I can rotate it and fit it underneath in the reverse direction?
How do I increase the solder hole sizes for the wires? Largest I found was 1.4mil's. Need to use this to add the mounting screw holes.
Is there a way I can erase the small little red and blue pieces that are sticking off the solder tabs?

Sorry if these ?'s seem stupid. Just taught myself Eagle tonight.
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Old 15th February 2006, 09:47 AM   #2
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First things first, your grid snap setting is too large. The 0.1 grid you used for layout is fine, but then for laying out tracks, you need to use some fraction of the pin spacing. in this case the LM3886 has a pin spacing of 0.125, so 0.025 would seem appropriate. Scrap your existing tracks and start again clean. It's not a big board so it shouldn't take that long. Oh, and personally, I would only use 45 degree bends, freeform angles look messy to me.

As for mounting holes, if you look down at the tool buttons on the left hand side, there is one there specifically for that purpose.

Get the redraw done and we'll look at your other Qs.
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Old 15th February 2006, 10:22 AM   #3
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The LM3886 and it's family do not have 0.125 inch pitch, as I found to my detriment when hastily laying a board out to imperial standard pitch. It is in fact an annoying metric pitch of 1.7mm (0.067 inch).

God knows why they chose such a pitch, it's sadistically close to imperial to fool the eye, but not close enough to physically fit

I agree with using 45 or 90 degree bends only, it does look a lot more professional, but each to their own. I have seen some nice boards that have used random angles.
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Old 15th February 2006, 10:28 AM   #4
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Just shows how long it is since I laid out a chipamp board! In that case, 0.033 would seem to be a good grid snap setting.
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Old 16th February 2006, 12:10 AM   #5
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Ok, so I fixed it, changed the pitch etc. Now the only problem, how do I copy it so I can put 4 on one board?

BTW, the hole button just gives me a +. How do I specify the hole diameter?

Thanks for the help guys
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Old 16th February 2006, 12:22 AM   #6
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Firstly, save your design under a new name, and use that version to work with so your original stays safe!

Holes - when you select the hole tool, there is a drop down in the menu bar to select the diameter.

Copying your design - Firstly turn on all the layers you need. Then drag a selection box over the components you want to copy. Click the scissors button, and then right-click inside the selected area. Close the Schematic and PCB windows, and then open a blank PCB window. You can then use the paste tool to duplicate as many as you need.
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