3D Printed Chassis

Jennifer G

Member
2015-08-31 2:31 pm
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).
 
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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.
 

Jennifer G

Member
2015-08-31 2:31 pm
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.
 
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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.
 

Jennifer G

Member
2015-08-31 2:31 pm
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.
 

Jennifer G

Member
2015-08-31 2:31 pm
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?
 

ChuckORWC

Member
2014-11-15 1:12 am
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.
 

rayma

Member
2011-04-29 8:37 pm
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?

That sort of noise can happen even with a shielded enclosure, and twisting the transformer wires,
while good practice, probably won't help it. It might take some tracking down, so first try a filtered
power strip for the amp's power cord, if you have one. If not, try using an extension cord to plug
the amp into a different, farther outlet, hopefully on a different AC line circuit branch.

If that doesn't work, try some filtering at the connection between the power cord and the transformer primary.
This would use a combination of special capacitors called X and Y capacitors that are specially designed
for use across the AC line. It's in a part of the circuit that is more dangerous to work on, though.
 
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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.

Thanks. I intend on designing a honeycomb PLA vent over the chip amp with a nice large heat sink distributing the heat evenly and upwards directly through the vent. The PLA melts at around 190C -- about 375F. I print at 210C.

I also intend on a honeycomb vent (circular) right over the antek toroidal power supply as well.

I can paint all the plastic any colors I like and am a fairly good craft painter. So I can make it say steampunk or gunmetal.. whatever I want. (Here's a quadcopter frame I printed in PLA and painted to be a rusty post apocalyptic metal: Micro 105 FPV Quadcopter - 8.5mm Motors, Micro Scisky by JenniferG)
 

ChuckORWC

Member
2014-11-15 1:12 am
Rayma,

Wouldn't an IEC with a built-in line filter serve the same purpose without having to deal with special capacitors or increasing the risks involved with mains wiring (any more so than with a standard IEC). As a bonus, many IEC line filters include fuse holders... Kill three birds with one stone!
 

ChuckORWC

Member
2014-11-15 1:12 am
The light switch noise is from a different circuit / branch, in the bathroom. But that branch runs overhead in the attic just about right over the amplifier (in the living room), to the front door of the house. Also a lamp on the same circuit as the amp causes a similar popping noise. It all seems to be about light switches for some reason.

I think when the air conditioner comes on it pops as well.. and that is on another separate 230V circuit. but it could be the central fan which is on 110V and might be on the same circuit as the bathroom light switch.
 
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I imagine you can get pretty creative with a 3D printer... I like creative cases (just don't go overboard).

I might as well print out a case for my B1 buffer to match :) i'd have all 3 cases the same foot print. Would be nice if I could stack all three but I don't know how a preamp would do under a transformer that's under an amp. The transformer doesn't seem to generate much heat, it's overly beefy too. 300va. It'd probably do okay under the amp with some feet on the amp.
 

rayma

Member
2011-04-29 8:37 pm
Wouldn't an IEC with a built-in line filter serve the same purpose without having to deal
with special capacitors or increasing the risks involved with mains wiring.

Yes, if there's a way to design provision for it in the plastic box. Digikey etc. should have plenty
of modular line filters for a 3A circuit like this. Most are for 10A, I think.
 
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Yes, if there's a way to design provision for it in the plastic box. Digikey etc. should have plenty
of modular line filters for a 3A circuit like this.

Yeah I can design it any way I like.. wish I had a CNC mill :) Well I am gonna build one eventually.. for around $300... the Mostly Printed CNC:

Mostly Printed CNC / MultiTool by Allted - Thingiverse

$240 for the kit bundle: electronics, motors, wires, connecters & screws.
Like $20 or something for the electrical conduit (used as rails)
and then $50-75 for the spindle. And then around $30 in PLA for the printed parts (bearing blocks etc).

But I have to justify the purchase.. figure how much I;d use it. What's nice about it is you can change the heads and make it a large 3D printer (btw it can be any footprint of your choosing). Can also, by swapping out the heads on the fly, make it a laser wood cutter, laser etcher, wood router etc.. list goes on and on :)
 
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