How small can I make a case for a LM3875 kit? - diyAudio
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Old 3rd July 2008, 02:43 AM   #1
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Default How small can I make a case for a LM3875 kit?

I was going to go for one toroid. Ideally I want the case to be as small as possible but I haven't found the dimensions of the Audiosector kit so not sure how big to make the case. I also want to put in some shielding around the toroid ideally. So any suggestions on internal dimensions required for the case?
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Old 3rd July 2008, 02:51 AM   #2
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Buy all the other parts first. Then you'll know!
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Old 3rd July 2008, 03:31 AM   #3
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My window of opportunity is limited so will be building the case first.
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Old 3rd July 2008, 08:04 AM   #4
Dxvideo is offline Dxvideo  Turkey
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You will need 200-250VA toroidal transformer. Theyre; 55mm height and 110mm dia.. If you add gainclones and power supply boards dimensions;
I think you will need 250 x 250 x 80 mm box at least.. Its so tiny.
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Old 3rd July 2008, 08:05 AM   #5
Nuuk is offline Nuuk  United Kingdom
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There is a stock answer for this sort of question - have a look around at what others have built.

There is a chip amp photo gallery in this forum, and another one at Decibel Dungeon.

Just be aware that a 'tight' design may be more challenging in terms of preventing hum etc due to the close proximity of the transformer to the amp circuit, and the close routing of the wiring.
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Old 3rd July 2008, 10:01 AM   #6
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Yep, have an idea of how big to make it (or how small). I wanted to make it as small as the case I will build for the tube pre amp/headphone amp but now I think it doesn't matter if it is bigger than it.

Peter himself recommended 9x9x2.5" (around 23x23x6.25cm) for the internal dimensions...
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Old 3rd July 2008, 11:45 AM   #7
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Quote:
Originally posted by m0b1liz3
My window of opportunity is limited so will be building the case first.
I'm not sure what that means, but building the case first will require it to be bigger than it needs to be unless you risk not fitting it all in.

Advice from first hand experience: buy the toroid before building the case or leave ample extra room. Many of them are bigger than advertised due to winding unevenness and the way the mounting plate fits. I had to cut up a mounting plate to get mine in a chassis after I thought I had 5mm to spare according to published dimensions.
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Old 3rd July 2008, 04:24 PM   #8
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This is about as small as I would think you can do.......

http://www.vikash.info/audio/tatca/images.asp

The smaller it is though the build will be much more fiddly.

John
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Old 3rd July 2008, 10:38 PM   #9
Vautrin is offline Vautrin  United States
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I'm convinced Nuuk has saved me from stumbling at the case-making stage. I had poorly planned my layout, trying to 'finesse' my Audiosector boards into the unforseen tight spaces. After reading this timely thread, I've de-crammed. adding a case for the amp boards. The chips (and I) should breathe a bit easier.

David in SW FL
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Old 3rd July 2008, 11:10 PM   #10
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I do have the advantage that I generally have drawings (dxfs) of any PCB that I design, but if I want to be sure things will fit together, I draw them in 3D.

You can do this in Autocad, but it's easier in SolidWorks.

Datasheets usually have accurate dimensions for components.

I believe some more recent PCB packages will show you a 3D view, but I haven't used one.

w
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