Step 1: Parts List and Tools
.50 cal Ammo Can
AMP ( Lepai LP-2020A+)
Set 4" car speakers (Kicker DS40)
12 volt Sealed Lead Acid Battery (UB1280)
12 volt switch (Amico Angel Eye White Led Light 16mm 12V Latching)
6 position dual row terminal block (Used to keep wires organized)
Old PC power supply (wire and connectors)
One 3.5mm male to female cable
12v cigarette USB charger
Screws/Nuts (#8-32 x ¾ Flat Head Phillips)
12v battery charger
Wire stripping pliers
Wire crimping pliers
Lighter for shrink tube
Step 2: Switching Wiring
One mistake I made that you can avoid, when selecting your switch make sure to choose a latching switch and not a momentary switch. If you order a momentary switch like I did the first time, your boombox will only fire up as long as you are holding the button down.
I wired and tested everything outside of the box. I elected to use some of the 4 pin Molex connectors from an old power supply, this is a quick easy disconnect that I know I can rely on. I just pulled the unused pins out of the plastic connector with pliers. I also used wires from the power supply rather than buying wire.
Wiring the Switch
***Disclaimer, I don't claim to have anything more than very basic electrical wiring knowledge and am not an electronics expert in any way, shape or form***
I used a 5 pin LED switch.
From left to right:
LED NEG | C1 (common) | NO1 (normally open) | NC1 (normally closed) | LED POS
Negative connection into switch (from battery) to LED NEG
Negative connection out of switch (to 6 post terminal block)
LED NEG to NEG of Molex attached to terminal block
Positive connection into switch (from battery) to NO1
C1 jumped to LED POS (this will turn on the switch LED when the switch is in the ON position)
Positive connection out of switch (to 6 post terminal block)
C1 to POS of Molex attached to terminal block
I ran wire to jump the POS and NEG connections to the other blocks in the terminal block. I used a terminal block to make things nice and neat, this is just my preference and is not necessarily needed. I checked the voltage at the battery and then at each one of the terminal blocks where I jumped it.
Step 3: USB Charging
The next step in the wiring was to repurpose the 12v USB charger. The reason I chose to use one of these was there is already a 12v to 5v converter made for you. I paid 1$ for a working charger. I opened it up and clipped the NEG wire connections and soldered them together. Next I soldered a longer POS wire. I put everything back together in the case, hooked to the terminal block and tested the output.
Step 4: Wiring the AMP
I saw some guys that soldered connections directly into the amp, as I said before I am not an electronics expert so I opted to snip the plug off the power cable and connect it to my terminal block. Since the cable was not marked POS and NEG here is how I tested. I hooked only one wire at a time to a NEG connection on the terminal block. I was able to determine the outside of my plug was negative by the wiring diagram on the amp above the plug. I held the black connection on my multi meter on the outside of the power connector and the red connection on a positive block on the terminal. If I get a reading on my meter, the wire hooked up is NEG and completes the circuit. If I don't get a reading on my meter, the wire hooked up is POS and did not complete the circuit. After determining and marking POS and NEG power supply wires, I hooked them to the terminal block. I tested once again to make sure I have a completed circuit before plugging into my amp.
Step 5: Final Wire Testing
So now with all the wiring hooked up outside of my box I hooked up the speakers and a 3.5mm cable to the amp and tested to make sure everything is in working order before cutting on my ammo can.
Step 6: General Layout
I decided on a general layout to make sure everything fit nice before making any cuts on my ammo can. I measured everything out and made a template with a piece of card stock using a tape measure and compass. After cutting out the template, I dry fitted the speakers to make sure the holes were the correct size...always measure twice and cut once, they don't give away ammo cans. Use the template to transfer the pattern to the ammo can. Use a drill bit to drill into the inside of each speaker hole to get the jigsaw bit in to cut out the speaker holes. After getting the holes cut out, I ran a file over the edges to take off any sharp edges.
After getting all of the metal file shavings out of the box and off my work bench (don't want the shavings sticking to the speakers) I dry fitted the speakers. After making sure they fit correctly, I marked and drilled holes for the screws to hold the speakers in place. At this point I also drilled holes to the correct size for my switch and 3.5mm aux input. Once again, make sure to clean out metal file shavings before putting the speakers back in the box.
Step 7: Putting It All Together
I used Sugru to hold the mounting screws in place for the amp. I didn't want to drill any more holes in my ammo can than I had to. I also marked and glued the terminal block in place. I let everything set for 36 hours to ensure it was dry. I took apart an old 3.5mm jack and installed it in the box. I cut and soldered all the necessary power cables to length. I used the self-adhesive Velcro to hold the battery in place.
Step 8: Some Thoughts
I have only had this build put together for a few weeks now. I have not fully discharged the battery so I am not sure how long my setup will last. From what I have read, it sounds like it should last 8-12 hours on a single charge. I have also added USB charging capabilities so this could dramatically cut down on runtime if you are charging you music device.
I plan on using my boombox mainly for camping and fishing. It is a bit heavy, so I wouldn't plan on strapping it to your backpack!
One thing I plan to add in the future is a Bluetooth receiver so you don't need to plug your phone directly to the box. I haven't found a good hack for the Bluetooth yet, I may need to purchase a receiver.