The car stereo boombox or "tradies boombox" is a popular project as many guys have collected the odd bit of car audio gear. When a friend gave me a Pioneer head unit out of his bunky old ride, I remembered the random parts I've accumulated over the years and knew I had to make one. My goal was to end up with something sturdy, attractive and versatile enough to run from multiple power sources.
After going through my assorted junk I sourced the following components for the build:
- Pioneer head unit (4x50w amp)
- 2x 4" speakers
- 2x 6" speakers /w grills
- PC case fan and assorted grills
- ATX power supply
- 1x SPST switch
- 1x SPDT switch
- Terminal blocks and assorted wire
- All purpose primer, red and matt black spray paint
This design uses the head units built in 4x50w amp through two 6" and two 4" speakers. Can play audio from a radio tuner, cd or external devices like iphones or mp3 players through an AUX connection. Powered from a built in PC power supply or using an external 12v power source like a cars lighter socket. I've got an older head unit and an auxilary connection isn't built in, I need to use an AUX cable to plug in external devices. The only items I had to purchase were the paint, radio antenna and AUX cable.
The power supply needed to be altered so I could use it with the boombox. After checking the ratings sticker on my junk PSU's I settled on this one. I've heard of others having issues powering car audio gear with PC power supplies however the system should consume well less than the 13A that this supplies +12v line is rated at and I'll ensure the enclosure has good air flow to prevent overheating. Keep in mind I'm only using the built in 4x50w amp. Using a separate amp would likely draw too much power.
As these are switched-mode supplies, a resistor needs to be added to ensure it's always under load and therefore provides a stable output. Refer to the ratings sticker and you can see the majority of the amperage is available on the +5v line (25A) therefore I'll add a 10w ceramic resistor to the +5v. This is an older power supply, modern PSU's will provide more amps on +12v. All the wires were cut and isolated except for PWR ON (green), GND (black) and +12v (yellow). These wires were connected to a terminal block. PWR ON will be switched to ground to turn the unit on.
If you want more details about converting a power supply, check out this DIY lab power supply tutorial which runs over everything you need to know. I tested the power supplies ability to run this equipment for an extended period of time and it performed well. Didn't get hot and the audio distortion that sometimes occurs when head units are provided with unstable power wasn't present.
I managed to find a decent length of 19mm MDF to build the enclosure. Ideally I would have used some thinner MDF or ply and make it a bit lighter but this will do the job. I toyed with idea of making it jukebox shaped but eventually settled on a basic compact box to keep the design simple and durable.
After sketching out the basic design and measurements, I cut all the required pieces with a circular saw. The enclosure is held together with wood glue, screws and small brackets. All the slots and holes were cut with a jigsaw and finished with a file. I recessed the front panel for a nice look and to offset the distance the components will protrude once installed.
The side 6" speakers are sectioned off into their own enclosures. Nuts are liquid nailed into place to allow the back panel to be secured with bolts. No idea how durable this is going to be however it's working well so far.
The joins on the inside are sealed with liquid nails and the whole enclosure was treated to some wood filler and a thorough sanding. Ports in the front were added for the power switch, power LED and auxilary RCA inputs.
The back panel had holes cut for the fan, power supply, speaker exhaust ports, DC / AC switch and external 12v connections.
Several coats of all-purpose primer were added with light sanding in between coats to get the smoothest finish possible. I added some vent holes on the bottom to allow air to be drawn through the device and keep everything inside cool.
The body of the unit is painted red with the back and face painted matt black. There's a few imperfections here and there but it I'm happy with the finish.
Once the whole unit was painted, it's time to install the components and wire the whole thing up. At this point I'm postive its going to be a tank of a device and some handles are going to be required to get her off the ground once fully loaded.
The diagram above shows how it's all wired together. The connections from the head unit to the speakers aren't shown:
- S1 - SPDT switch. Switches between the internal dc input from the power supply or the external input.
- S2 - SPST switch. Connects PWR ON to ground to turn the power supply on and provide the unit with power.
- R1 - 1k ohm 1/4w resistor. Provides adequate protection for the LED for up to 15v input.
- D1 - Red 5mm LED diode 2v 20ma. Indicates when the stereo is receiving power.
To arrange the wiring neatly and allow for simple modification or repair at a later date, terminal blocks, wire nuts and wire clips have been used.
As a finishing touch, a padded seat was added so I can have both tunes and a comfortable place to sit with a beer.
The switch on the back alternates between the built in PSU's power and an external power source. If you connect a battery or other 12v source to the two protruding bolts and flick the switch, the unit will be running from external power.
I've been contemplating adding a bottle opener to the front. It sounds great and gets pretty loud. The battery connector for the head unit doesn't receive constant power therefore it forgets the settings when you turn it off. I may have to come up with a solution for this but for now it will manage.
Consider following me on twitter.