Free formed circuit protected by a brick of crystal clear resin

The look of this crystal clear resin brick is pretty amazing. [Rupert Hirst] decided to encase his amplifier circuit in a block of polyester resin. We just hope he got everything in his circuit right because there’s no way to replace any of those parts now!

He deserves a lot of credit for working out a visually pleasing way to mount each component. There wasn’t any type of substrate used, but a few lower gauge wires were picked as the rails and they add some mounting stability. Before casting, he took the case of each of the three jacks apart and sealed the seams with some of the casting resin to prevent the final pour from filling them up.

Eagle CAD was used to design the mold. He printed it out on some card stock, then used a hobby knife to cut the pieces out and super glue to assemble them. A second layer of super glue was run on each seam to ensure they’re water tight. After the casting was made [Rupert] spent plenty of time sanding, routing, and polishing the brick to achieve this look.

This makes us wonder about heat dissipation. Do you think it will be a problem? Tells us what your opinion by leaving a comment.

59 thoughts on “Free formed circuit protected by a brick of crystal clear resin

    1. Actually here’s a thought toward improving the process somewhat; put all electromechanical parts on an endcap piece that connects to via a header block. Not quite as cool but would be less hassle and would make it possible to use pots/switches/other jacks.

  1. Holy crap!
    I love it, that is a awesome idea and it looks amazing!
    The details look a bit off but (as i guess) for the first try at something like that, impressive!

  2. Heat dissipation ? There is nothing there that will get hot – and actually the resin conducts heat quite good! It looks really cool, but there is absolutely no shielding, so bringing a cellphone close is not so smart…

    1. Heat dissipation ? There is nothing there that will get hot

      It’s an amp. All amps need to get hot are electrons and a little bit of resistance in the wire.

      A classic cMoy has a peak current of about 40mA and a 9v battery. Combine those to get power, and you have about 360mW, or about a third of a Watt.

      A third of a Watt is about 1300 Joules per hour, or 22 Joules per minute. 1 Joule is enough energy to heat 1cc of water 1 degree C, so at most, this amp could channel enough power to heat 22cc of water at a rate of 1 degree C per minute.

      I doubt that would be a problem, but the parts that could potentially get hot are buried deep, and resin is a good insulator. Any heat will stay close to the components that generate it. While that might not cause component failure, it will cause the resin at the center of the block to expand, with a possible risk of causing the plastic to crack.

      My suggestion is to measure the temperature with an IR thermometer, run the thing at full power, and measure it at 1 minute, 5 minutes, 10 minutes, 30 minutes, and 1 hour (assuming you don’t see any alarming readings). Keep taking readings until you see the curve flatten out, at which point you’ll know that it’s reached a point where it dissipates heat as fast as the amp generates it.

      You may see nothing.. if so, enjoy, and props for a beautiful build. If you do see a rise in heat that causes you concern, dial back the power until you get a curve that looks comfortable.

      1. I was going to pile on here too :) also sorry miscliked report, it’d be good if there a js pop saying are you sure.

  3. Brilliant build.. Looks really slick.

    Depends on the wattage? I would guess that it may not be a huge issue. If it is then I’m sure that the design could always incorporate a heat sink cast into the case. ;)

  4. Heat dissipation should improve.

    The thermal conductivity of air is 0.025 W/m*K, and polyester resin is roughly 0.25 W/m*K.

      1. for small components that experience no forced convection, they are in a “free” convective state.

        When in the free state, the heat transfer coefficient ‘h’ in Newton’s law of cooling is actually found using the thermal conductivity ‘k’ that is found in conduction heat transfer.

        For cases like these, you can reasonably assume that air would act almost like a stagnant body similar to a solid.

  5. The Resin curing would produce enough heat that anything inside sensitive to it would have damaged itself.

    Resin hardening is exothermic reaction.

      1. I did read the description, and was answering it. There is no heat concerns if the project made it past the exceptionally high temperature resin curing. I guess you decided not to read the description and posted like a jackass.

  6. I wonder if it is water or impact resistant; since no water can get onto the circuit sans on the connectors.

    1. I’ve read that this is basically what the US military does to the electronics in missiles to allow them to withstand the G forces of…being in a missile.

  7. This is a great idea! I can’t imagine heat dissipation being a problem. As zaprodk mentioned, there’s really nothing that’s creating heat.

    Very inspiring! I may have to give this a try in the next round of “hacks”… with the glow of a nice blue power LED to let you know it’s active. :)

    Nice job Rupert!

      1. That sounds fun, but don’t motorcycle indicator bulbs get very hot? Correct me if I’m wrong, but aren’t they somewhere between 15 – 30w… inside a resin casting, IMHO they won’t dissipate heat fast enough, you might have a sticky resin mess on your bike ^.^

  8. Quite possibly one of the most beautiful electronic pieces I have seen… I think you’re on to something here!

    Any idea if you’d consider making more of these and what the balpark sum might be? I’d likely be interested.

  9. I love the look, and would like to do it on my preamps, but I would never do an unshielded build.

    As an example.. I have an old Creek Audio 4140 integrated amp. The case is wood, and unshielded. Though the PCB might have a ground plane (which helps).

    Every once in a while a trucker would drive by with an apparently really powerful CB and it would blast through my stereo completely unattenuated (max volume). It would really wake you up when you were dozing on the couch at 2AM (“hey good buddy, wake up and get off the couch!”).

  10. DAW, DUDE! THAT LOOKS SO SWEET! Mad props, dog, I’m super jelly. Besides that, one of the first things when I saw this was heat dissipation. Looks like we’ll have to wait and see

  11. From these (and earlier) pictures it looks like a fairly simple CMOY amplifier or a close relative, albeit wall rather than battery powered. CMOYs generally don’t churn out anywhere near enough juice to create much in the way of heat. The encasement could be a problem for highly current biased class A headphones amps, though.

    Or almost any kind of speaker amp, really.

    Anyway, it’s an awesome and well executed idea, so props to the creator.

  12. I am impressed.
    That’s actually not happening too often, not even here, but this is a wonderful example how you can fit a project into a package. The idea is simple, so simple in fact that I could have had it. And while I have sunk circuits in epoxy before for practical reasons and have built free wiring stuff, I never thought of doing it in this aesthetically pleasing way.

  13. I am also very impressed at the clean look, being that this is a head phone amp I don’t think heat will be problem.

    I will agree that the one on only thing I wold do is to add a 400-500nm LED for effects. Nothing lower or the UV might yellow the acrylic.

    I would love to make a USB flash drive in the same manner.
    Caio

    73′s
    De KG4MXV

  14. only problem: if any part fails you have to build a new unit so you may want to add extra protection such as a diode in series with the power connector and the amplifier chip so you dont blow it or the capacitors by reversing the power wires if you should ever have to replace the power supply with one of them universal power supply you can get at any electronics shop.

    if the unit takes has a max of less than 12 volts you may want to use a voltage regulator to prevent over volting it if you should use the wrong setting on the universal power supplies.

    most universal power supplies are a wall wart with a voltage selector that goes in 1.5 or 3 volt increments and are rated for up to1 amp and polarity can be set by a selector switch on the unit or reversing the plug tips.

    they also make and sell universal power supplies for use in the car they plug into the lighter socket and work the same way.

  15. Had to do some like this in college.

    Expensive as hell.

    Boring to sand.

    Used a dumber method. created piece in wood by hand. Negative silicone mold. resin piece.

  16. You could clamp this thing into a CNC machine and engrave the resin with some neat patterns – If you had included a bright RGB LED in there the engraved patterns would internally reflect and make some awesome colour light show that could react to the frequencies passing through the opamp!

    I love this as it stands though.

  17. I wonder… would a cap last longer sealed up like that?

    Very nice work. I’m curious to see how it ages. Will the resin discolor over time?

    Guess I should go read his page and see what’s already known!

  18. so what if something starts overheating? drill some holes near the problem components and pump cool water through. acrylic blocks always seemed cool to me, as in, a good thermal conductor.. but my cold cathode tubes, not so much. i’m not googling or wikiped’ing to correct a mistake before i make it, but i’m guessing the tubes are made with cyanoacrylate somehow, because hitting them with a torch made them expand strangely, releasing the stench of superglue.

  19. Amazing piece of craftsmanship. If you ever plan on making more I would be very interested in procuring one for myself.

  20. It would be cool to see a heat sink protruding through the top of the resin. (at least I think so) and the heat generating components could be attached to that.

  21. Reference potting/encapsulant comany white papers on their use. Lots of things to note and/or beware of.

    Some shrink/grow when curing. All get hot so take note of temperatures. Some components like generic electrolytic caps (vent), resonators (mechanical interference), LEDs (chemical)etc. can not be encapsulated.

    Regarding heat, most encapsulants are made to dissipate heat. Standard A/B epoxy resins are not and work quite well to insulate heat sources.

  22. That’s a beautiful build.
    I’m of the opinion that the more electronics encased in resin the better.
    I’d love to see a build where someone encases an entire motherboard in resin and just has heatsinks poking out through it.
    All media players should have resin, at least around the headphone jacks so they stop breaking.

    More resin!!! :D

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