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Old 28th March 2016, 02:58 AM   #1
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Default 3D Printed Chassis

Hello,

I now have a well tuned 3D printer -- Monoprice Maker Select V2 for $349.

I have Sketchup/CAD experience and can easily draw up an enclosure.

My printer's max build volume is about 8x8x7 inches (200mm x 200mm x 180mm).

With these materials and maximum dimensions, would it be possible to design a decent case for my LM3886 chip amp?

I'd have to do two different cases because of the 8 inch footprint. I could bolt them together internally and run the cables through a hole I make in the relevant sides of each.

I can make vents on the top -- say a honeycomb grill.

All this would be PLA plastic though. And I am concerned about shielding.

Would it sound better if it was inclosed in a steel case? OR can I line the plastic somehow with say foil tape to help? Or can I just shield everything internally?

The pair of custom designed cases (bolted together let's say) .. would cost well under $10 in plastic PLA filament. Saving me a couple hundred dollars compared to a steel and/or aluminum case.

Accuracy of prints have been within 2 hundredths of a millimeter (so pretty good).

Last edited by Jennifer G; 28th March 2016 at 03:03 AM.
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Old 28th March 2016, 03:24 AM   #2
Enzo is offline Enzo  United States
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Ask yourself this question: is your 3D printer there to make something you need, or are you there to give the printer something to do?

And that $10 chassis, well you can't ignore that the printer cost $350, so you are only saving money once you have made a number of these things.

Just my own opinion, and others may disagree, but I wouldn't make an audio circuit in a plastic box. And if you go so far as to try to line the enclosure with shielding, then it seems we are skewing our priorities.
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Old 28th March 2016, 03:26 AM   #3
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Quote:
Originally Posted by Enzo View Post
Ask yourself this question: is your 3D printer there to make something you need, or are you there to give the printer something to do?

And that $10 chassis, well you can't ignore that the printer cost $350, so you are only saving money once you have made a number of these things.

Just my own opinion, and others may disagree, but I wouldn't make an audio circuit in a plastic box. And if you go so far as to try to line the enclosure with shielding, then it seems we are skewing our priorities.
My printer is here to make stuff I need. I need an amplifier enclosure and the printer is capable of printing one. But it's plastic, so that's why I asked here...

I already own the printer, I use it for MANY other useful things. So my cost is only like $5-10 in plastic. I print more things on this than I do my laser printer. Watch, they'll be commonplace in like 5 years.. 1/2 households will have them and 5 yr olds will be designing stuff in CAD. Also, fortunately the printer I have is totally OpenSource (along with a large community base) with easily replaceable/affordable parts.. I even have the source code to the firmware and know digital electronics and programming languages .. so this printer will last me the rest of my life.

I appreciate your third paragraph though, but waiting for others opinions as well. Thanks.

Last edited by Jennifer G; 28th March 2016 at 03:34 AM.
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Old 28th March 2016, 04:15 AM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by Jennifer G View Post
With these materials and maximum dimensions, would it be possible
to design a decent case for my LM3886 chip amp?
Give it a try. If the amplifier's pcb and the rest of the wiring is well done,
the plastic case without any shielding shouldn't be much of an issue.
The signal levels are fairly high in that circuit.

Last edited by rayma; 28th March 2016 at 04:20 AM.
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Old 28th March 2016, 04:26 AM   #5
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Take a look at the consumer electronics you already have. Virtually none of them use metal cases! Plastic should be fine. You might want to consider how to support the heavy parts like the power transformer. So a bit of bracing may be required. The other trick is to make a shelved lip to allow the halves to interlock. With voids on 1/2 and bumps on the other no fasteners may be needed.

The safety ground can go directly to the transformer mounting bolts.
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Old 28th March 2016, 04:32 AM   #6
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Quote:
Originally Posted by simon7000 View Post
Take a look at the consumer electronics you already have. Virtually none of them use metal cases! Plastic should be fine. You might want to consider how to support the heavy parts like the power transformer. So a bit of bracing may be required. The other trick is to make a shelved lip to allow the halves to interlock. With voids on 1/2 and bumps on the other no fasteners may be needed.

The safety ground can go directly to the transformer mounting bolts.
Thanks, have any photos by any chance of what you're talking about with respect to the interlocking pieces? So I can see what ya mean.

EDIT: the plastic is fairly rigid with a honeycomb network infill.
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Old 28th March 2016, 04:36 AM   #7
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Enzo, here's an example of what I use my 3D printer for. Printing this right now on it:
Breadboard Spring Vise by patshead - Thingiverse
https://www.youtube.com/watch?v=zAxuUaHodjY

I love this thing! Easily secure any loose pcb to the board for quick work.

Last edited by Jennifer G; 28th March 2016 at 04:39 AM.
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Old 28th March 2016, 04:42 AM   #8
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Quote:
Originally Posted by rayma View Post
Give it a try. If the amplifier's pcb and the rest of the wiring is well done,
the plastic case without any shielding shouldn't be much of an issue.
The signal levels are fairly high in that circuit.
Only thing, as is now, with no case at all (been running it this way for months by the way), I get popping noise when certain lightswitches are turned on in the house.

I don't have the wires running from transformer to rectifier twisted.. just straight. If I twist them should that help eliminate that noise?
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Old 28th March 2016, 04:55 AM   #9
tomchr is offline tomchr  Canada
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If using a chip amp circuit with high power supply rejection ratio (so, say an LM3886 with some "secret sauce" applied) one could also entertain the idea of using a switching supply. That'll save some weight and space. You'll still need to provide a heat sink for the chip amp, though. - Or go Class D on the amp as well.

Tom
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Old 28th March 2016, 04:58 AM   #10
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It's only $5 - $10 bucks in material, and a little time investment in design, so why not try it? Contra Enzo, I see no skewing of priorities in adding foil for shielding, as it's commonly done for wood enclosures. Besides, only you can set your own priorities, and decide how to skew them

To determine if shielding will be effective with your popping issue, you might try constructing a simple enclosure (like a foil-lined cardboard box) to see if it helps. If the "certain light switches" are not in close proximity to the amp, though, my guess is it's line noise and not an EMF issue. Maybe a line filter will help?

Another thing to consider is the heat generated by the amp and its effect on the PLA material. I know this isn't a class A amp, but some of the components might generate enough heat to be of concern... this can probably be addressed in the design.

Anyway, sounds fun. Go for it.
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