This instructable is on building a 2.0 portable bluetooth Boombox.
For this build I sourced parts locally as well as from China.
In this build I've given two bass port at the bottom. The speaker is powered by a 12V 7Ah Sealed Lead Acid Battery and is having Bluetooth V2.0 + EDR connectivity. This might run for somewhere around 15-20 days on moderate volume. It weighs somewhere around 6 kgs.
I was aiming for a vintage radio look.
Hope the instructable will be informative enough.
Step 1: Material and Tools
List of Electronics:
- Amplifier Board (Aliexpress, 2*15W TDA7297 Dual Channel)
- DC-DC Step Down Converter (Aliexpress, LM2596 Step Down Converter)
- Full Range 4" Speaker Drivers 10W 8Ohm (Local Seller)
- Bluetooth Stereo Adapter Audio Receiver with AUX Cable
- Digital LED Voltmeter Panel
- 12V 2A AC Adapter
- 12V 7Ah Sealed Lead Acid Battery
- 12V Battery Charger
- 3 On/Off Switch (Single Pole Double Throw Switch)
- 3.5mm Female Jack
- Plug Male & Female
- AC Adapter Female Jack
Tools and Materials:
- 8mm MDF Board
- 2.5mm MDF Board (For Grill, Control Plate and Back Panel)
- Brown Rexine
- Soldering Iron & Solder
- Wire Snipper
- Screwdriver Set
- Rubber Glue
- Glue Gun & Glue Sticks
- Wood Polish
- Leather Polish
- Wire Shrink Wrap
- Aluminium Volume Knob (Turned in College)
- Acrylic Paint
- Laser Cutter
The Final Dimensions of the speaker is 35cm x 18.5cm x 18.5cm.
Step 2: Cutting the Panels and Turning the Volume Knob
The enclosure panels are cut out of 8mm thick MDF board.
Dimensions for each panel is given in the images above. All dimension are in centimeter (cm). All the steps and slots are 4mm wide and 4mm deep. Top, bottom, left and right panels have double rabbet joinery.
I used a table saw to cut the outer dimensions of the panels. Then used a wood router to cut 4mm wide and 4mm deep rabbet.
I cut 3 pieces to enclose my battery. Cut pieces according to the size of battery you are using.
I drilled holes in the bottom panel for bass port. According to the frequency you are try to achieve make desired holes. You'll have to try and test the length of bass port. There are software available online using which you can calculate the length of bass port.
Volume knobwas turned out of aluminum. The diameter of the knob is 3.5cm and the height is 2 cms. A hole was drilled on the bottom to fit the knob of potentiometer.
I've also put an image which will give you rough idea about the way the panels will join.
I've attached the back panel and grill lasercut CAD files. I used 2.5mm MDF for lasercutting. You can change the slots made in the back panels according the the shape and size of ports you are using.
- Black Lines: Through Cut
- Vector Cutting
- Power: 100
- Speed: 9
- Frequency: 1250
- Red Lines: Half Cut
- Vector Cutting
- Power: 50
- Speed: 75
- Frequency: 1250
Red lines are used for branding and labeling the controls. So, we just need them to make a mark on MDF.
Step 3: Preparing the Different Components
The block diagram for the system is given.
Wiring the Amplifier
Positive from the On/Off switch is connected to the positive on the board. Negative from the AC jack, Battery, Bluetooth receiver is connected to the negative on the board. I soldered an extra led on the led points on the amplifier. I soldered the speaker wires on the board instead of inserting them in the slots, as the wires kept on coming out front it, but this was done once the speakers were put on the speaker mounting panel. I desoldered the existing 50K potentiometer and replaced it with a 20K one to increase the volume level. I plugged in a 3.5mm aux cable from the bluetooth receiver module into the 3.5mm audio in port on the board.
DC-DC step down converter
Step down converter was given power from the master On/Off switch. You'll need a multimeter to set 5V output by tuning the potentiometer on the converter. The output pins of the converter were soldered to the power terminals of the bluetooth receiver module.
Bluetooth Audio Receiver
Receiver is powered by the DC-DC step down converter and the audio signals from the device connected is fed into the amplifier using an aux cable connected to the receiver. You can solder a wire to the antenna of the module to increase the range. A 10 cm wire would be enough.
I connected the voltmeter between the positive from the master switch and the negative of the battery. So, it will switch on only when battery is selected as the power source.
Power Source Toggle Switch
+ive from the battery and AC jack are connected to the side poles of the SPDT. The center pole of the toggle switch is connected to the master switch side pole. I've attached an image showing the wiring.
Master On/Off Switch
Output from the power source toggle is connected to the side pole. One wire from the center output pole is connected to the positive on the amplifier board, one is connected to the positive of the Voltmeter and one is connected to the Bluetooth On/Off switch side pole.
Bluetooth On/Off Switch
Output from the master switch is connected to the side pole. The center output pole is connected to the positive input on the DC DC step down converter.
Connect the aux to the back side of the 3.5mm port on the amplifier board. The pin closest to the face of the port is the ground terminal and the one's below are left and right channel terminal.
Battery Charger Plug
Connect the +ive and -ive terminal of the female charger plug on the +ive and -ive terminal of battery respectively. Attention: Make sure that you connect the polarity of the charger correctly or it may lead to accident.
After desoldering the 50K potentiometer and putting a 20K potentiometer I found out the only one of the channel was working and when the potentiometer was kept at zero position I could still hear music. The potentiometer head contact point had become loose and one of the control wire was disconnected. I had to put another one. So, before closing the enclosure make sure that both the channels are working and when the knob is at zero position no sound comes out of the speakers.
Step 4: Assembly
To assemble the speakers follow the steps
- Hot glue the speakers on the back side of the speaker mounting plate.
- Take the bottom panel and left panel, put wood glue on the rabbets and align them. Glue the bottom and left rabbets on the speaker mounting panel and insert it into the left and bottom panel slots.
- Put glue on the right panel rabbet and slot and insert it in the speaker mounting slot and alight it with bottom panel.
- Put glue on two sides of corners and place it between the panels.
- Use the blocks you have cut for your battery enclosure and glue them to the bottom panel.
- Put glue on the side rabbet and the slot on the top panel and align it with left, right and speaker mounting panel.
- Use nails on the corners to strengthen the fit of panels. You can drill holes also on the side of the panels and corners and then use screws to secure them.
- Once battery enclosure is dry place the battery in it and hot glue it so that it cannot move.
- Cut the rexine to fit the enclosure. Using rubber adhesive wrap the four panels with rexine. Keep some extra rexine on the sides to cover the edges. Be careful when wrapping the edges. I made 45 degree cuts on the edges so that it looks clean.
- Mount the switches, potentiometer, LED and 3.5mm female jack on the Control Plate in the order shown in the picture. Hot glue the components on the back side of the plate. Put a bit of hot glue in the turned aluminium knob and insert the potentimeter knob in it.
- Mount the control plate with the switches and potentiometer on the inner side of the top panel using screws. Use hot glue on the edges on the plate.
- Solder the speaker wire to the board.
- Place the voltmeter, battery charging female plug and AC jack on the back plate using screws or nuts provided with the ports. Solder the connections as instructed in the previous step.
- Hot glue the amplifier inside the enclosure according to the space available. You can also screw the board as well.
- Hot glue the bluetooth receiver module and DC-DC converter to one of the panel.
- Insert the bass port tube. I used a very thick millboard. And made it into a tube and glued it to the holes for bass port.
- Screw the back panel using 6 screws. Four corner screw were inserted into the corners. So make sure that the holes you make in the back panel is aligned to the hole drilled in the corner edge. For the center screw you might have to give 2 additional 8mm MDF tabs in which screws can be inserted. I used 6 screws cause the bass in the speakers was making the back panel rattle a bit. You can use a thicker 4mm MDF as well for the back panel.
- On the front of the speaker mounting panel put 4 pieces of 8mm thick MDF (3cmx3cm). Drill holes (smaller than the dia of screw) in these pieces according to the holes on the grill.
- Screw the grill in place.
Step 5: Finishing Touches
I made footpegs using 1.5 cm wide and 17 cm long 8mm MDF. Then I superglued them to the base and drilled two holes in each footpeg Counter sink the holes so that the screws are inside the footpegs. I inserted 2 cm long screws so that they penetrate inside the bottom panel.
I painted the front of speaker mounting panel and the 4 grill mounts using white acrylic paint.
Using emery paper sand the grill and the back panel. I had lasercut my brand name Sonic Architect and superglued it to the grill with the help of marking I had made during laser cutting. Be very careful while supergluing the brand.
Apply wood polish to make the grill and front panel smooth. Polish the rexine using leather polish.
Check once that every thing is working properly. If it is then screw the back panel and grill.
I thought that I'll give the boombox a leather strap as handle but for some reason I haven't gone ahead with that. If I do add it I'll update the instructable.
Switch on the boombox, connect your phone and you are good to rock the party.
Any questions, comments or criticisms always welcome!