I wanted to put my old boombox out of commission in exchange for a bigger, louder system that I could connect to my smartphone wirelessly. However, the average bluetooth stereo system goes for $100 to $300, well outside of my price range. With some hunting and some patience, this system can be built for as little as $25.
Step 1: Materials and Tools
For this project you'll need:
- Lumber (pallet wood works well)
- 12V 5A Power Supply (amperage will need to be matched to your amp)
- Car Audio Amplifier
- Bluetooth Audio Receiver (http://www.amazon.com/gp/product/B00HT07QXI/ref=oh...
- 3.5mm to RCA Cable
- Fasteners and a Rubber Grommet
Tools you'll need include:
- Jig Saw
- Soldering Iron, Wire Nuts, or equivalent
While they aren't necessary, these tools will definitely help accelerate the process:
- Belt Sander
- Table Saw
- Caulking Gun and Caulk
- Drill Press
Step 2: Gathering Materials/Bench Test
The most difficult part of this build will be finding a cheap amplifier. I managed to find a Coustic 102 amp along with two 6" house subs from a swap meet for $1 since the amp was originally not working. Your best bet will likely be to hunt through swap meets, garage sales, and craigslist. The Coustic 102 I found has a max output of 40 watts per channel at 2 ohms per channel.
Once you locate an amplifier you'll need to find a power supply. The owner's manual should be referenced for voltage and amperage specifications (google is your best friend here). If an owner's manual can't be found check the amp's fuse for the amperage, and if you have an amp made for car audio the input should 14.4 volts (12 volts will work). The positive output from the adapter will be connected to both the positive input and the remote on/off from the amp. Power for the bluetooth receiver is best supplied by a standard usb wall adapter. Both adapters should then be wired in parallel with the main power cord (all positives should be wired together and all negatives should be wired together).
After the power supply has been sorted the bluetooth receiver can be hooked up to the power supply and connected to the amp using a 3.5mm to RCA cable. Your speaker arrangement will depend on the amplifier you select as well as your speakers. Again an owner's manual should give you all the info you need as far as what your amp can handle.
In order to figure out your speaker arrangement you'll first need to understand how to add the resistance of the speakers. Resistors in series add together normally. However, resisters in parallel are added by taking the reciprocal of each resistor, adding the reciprocals, and taking the reciprocal of the sum, like so: 1/R1 + 1/R2 = 1/Rt. For example, two 4 ohm speakers wired in series will result in 8 ohms total, where as the same two speakers wired in parallel will result in 2 ohms total. While a lower resistance will generally allow more power to be supplied to the speakers, not all amplifiers are stable at lower resistance values, again the owner's manual should be referenced.
Once all of the above has been accomplished a bench test should be performed. Check for any crackling, popping, or other distortions and check your connections as needed. Make sure to be thorough as the system will be more difficult to troubleshoot once it's placed in the enclosure.
Step 3: Building the Enclosure
For the enclosure I used a sheet of plywood I had on hand and some wood pulled from old pallets. Try craigslist for free pallets and scrap wood. Building the enclosure is pretty simple. Remember to drill pilot holes before driving screws into your enclosure. This will help keep the wood from splitting and splintering. When deciding on the location of your speakers, try to route them away from any power wires and away from your bluetooth receiver.
Since I built this system to go in my garage, I took a few extra steps to help protect it against the elements. Once the bottom of the box was assembled I placed a bead of caulk along the inside edges of the box. Also, a coat of clear wood sealant was brushed onto all the inside faces. Finally, I used a rubber grommet to help seal the hole for the power cord.
Step 4: Finishing Touches
Once your enclosure is built all that's left is to finish the outside and mount your system inside. I went with a coat of black spray paint, but there are a wide variety of stains and paints available to choose from. Hot glue works well to mount the parts of your system such as the power supplies and bluetooth receiver that don't have screw mounts. For the speakers I chose to use black allen drive screws with chrome washers to give the outside a nice, finished look.
This project took about two weeks to complete once I had all the materials. Building the enclosure was the longest step as I had to wait for the caulk, sealant, and paint to dry in between steps. This is a good project for anyone who's new to carpentry and/or sound systems. Thanks for checking out my first instructable and good luck!