Introduction: FA2B (First Aid Boom Box)

About: Thermal and renewable energy engineer, Music and bike lover..

Hi guys, this is my first instructable so please be nice! I have recently bought a SMSL SA50 T-amp. Performance of this little amp is really impressive considering its size and price. I recommend it. After using it with my home speakers, I started looking for a way to build mobile speakers using this amp. My specifications are:

  • Sturdy and impervious box to contain the amp
  • Using either battery or DC to power the amp
  • Great quality of sound!

Step 1: Supplies

The box

I have used two military French first aid boxes. They are water proof and very strong. I have bought them in a military surplus.

The speakers

I have chosen Focal isc 100 speakers @ 40W RMS up to 80 W. The frecency responce looks good and their 93mm of recessed diameter correspond exactly to the size of the box. I bought them on Price Minister.

The batteries

SMSL SA50 has to be powered by 24 VDC. 24 VDC batteries are too big and very expensive. So, I have chosen to mount two normal 12VDC Li-po batteries of 6.8Ah in series. I have bought them on Aliexpress.

Other stuff

I have bought every electrical component on Farnel (2.5mm² wire, DC jack plug, 3.5mm jack plug, switch, RCA, terminal…). Finally, I bought silicone, paint and bolts in a DIY shop.

Step 2: The Box

To cut the box I made a muster diagram using a drill, jigsaw and grinder I cut the holes for speakers. That was a quite difficult step and the circles are not perfect but the speakers fit well. Then, I have cut an aperture on the bottom of the first box and on the top of the second to let the air pass through the two boxes. I have sealed the two boxes together with silicone and added 6 bolts to strengthen the structure. After making the cuts and drilling, I sanded down and painted the box before inserting the components. I used hammered effect paint, which I think gives volume to the metal.

Step 3: Inside the Box

Inserting the amp was a really difficult step! The holes that I have drilled are ugly and the more I tweaked the knobs of the amp, the worst it got. So I used the amp face screws to mount it on the box. I have kept the original foam protection around the amp: it does not heat because the power supply is external. Therefore it is protected against potential heat damage.
Wiring the speakers was easy, just weld the wire on the speaker connection and plug into the banana plug amp. After that I wired the RCA of the amp to the female jack frame. For the electrical part I made the mounting shown on the diagram in the first step, including a battery switch DC jack frame and rechargeable battery frame. I used a terminal to mount batteries in series and a switch to allow use of either batteries or AC power. I promise to add more wiring pictures soon.

Step 4: Painting

I applied 3 coats of paint.

Step 5: Paracord

Two metallic handle are already on the boxes. I simply linked them with paracord to make a phone holder.

To conclude, I'm realy surprised by the acoustic power and quality of the speakers and amp. Loud are nice and doesn't need bass-reflex or passive radiator to boost them.

Thanks for reading =)

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