DIY: Retro Hi-Fi Portable Speaker
Use with Any iPod or Smart PhoneDifficulty: Intermediate
Assembly Time: 6 hours
Got an old speaker gathering dust in the garage? With this project you can convert that old bookshelf speaker into a retro stereo. The sound system, with an integrated audio amplifier, battery and charger, can be used with any iPod or smart phone.
Required Components and Tools:
• 0.5Ω resistors
• Soldering iron and solder
• Sealed Lead Acid battery 12V
• 18V Laptop power supply
• Sheet metal
• Rubber feet
• 6-32 wood screws
• 22 gauge stranded wire
• A bookshelf or equivalent speaker
• Heat sink
|Part Description||Manufacturer Part No.|
|Audio Amplifier IC||TDA2002V|
|DC Power Jack||HD2388C|
|Toggle Switch, DPDT||1MD1T6B11M1QE|
|Toggle Switch, SPST||T100T1B4A2|
Step 1: Speaker Enclosure
Take everything out from inside the speaker. If the speaker is a multi-speaker cabinet, remove the crossover. Mark and drill holes on the long side for the handle.
Measure the spacing and diameter of the hole in the back of the speaker. If the speaker has permanent wires, you may want to drill a hole large enough for switch and jack mounting. If the speaker is wooden, the thickness may require a metal plate. You may want to draw a template in AutoCAD for the plate holes. You also may want to fabricate a small aluminum bracket to hold the battery inside the case.
If the enclosure is metal you probably won't need a plate and could mount the switch and jack through the cabinet directly.
Step 2: Building the Circuit
Click for larger image
You may use a perfboard or create your own PCB using the schematic.
When you wire the switches and inputs, use enough wire for external mounting. To prevent excessive heat, use 22 gauge wire or higher.
The amplifier is taken from the datasheet for the 10W audio amplifier IC. Designed for a car radio, this IC works well with a line-level input from an iPod, smart phone or laptop. Most sources are stereo yet this is a mono-speaker; R9 and R10 serve as a passive mixer circuit to combine the stereo signals into a mono signal.
The lead acid charging circuit uses a LM317T variable voltage regulator IC. It controls the current to an optimum level of charging from the laptop power supply to the battery. When the battery nears full, the battery voltage increases and the circuit delivers less current to "trickle charge" the battery further and maintain full charge without damage.
If the preference is to control volume from source, eliminate the volume control by soldering a wire from the center potentiometer hole to the other potentiometer hole not connected to the ground plane to pass the circuit through.
For speakers with a crossover, solder some wires to the old wore hookup location so the crossover can be connected to the PCB. For LC crossovers, the inductor goes in series with the woofer and the capacitor goes in series with the tweeter. Whenever possible, leave the original wiring in place.
Caution: Tune the trimpot while measuring the current through the battery with an ammeter so the current through the battery is 1/10th the Amp-hour (Ah) value of the battery. Over-current charging can cause the battery to vent hydrogen gas, which can trigger an explosion.
Step 3: Testing the Circuit
To test the battery charger, turn the potentiometer counter-clockwise all the way to minimize current to the battery. Connect 18V DC to the circuit and connect the battery with an ammeter in series. Turn the potentiometer clockwise until the current reads 1/10th the Ah rating of the battery. As the battery charges, the current should gradually drop. The current might be flowing in reverse to what you might expect when you connect the (+) of the ammeter to the (-) of the battery, but this is how it works.
To test the amplifier, connect the speakers to the source of music. To test with a volt meter, test voltage at the 3.5mm jack.
Step 4: Assembly
First, put the battery into place. Drill pilot holes wherever possible for the wood screws.
Mount the PCB on small plastic standoffs so they are not sitting directly against the wood. Nylon washers work perfectly. Position the PCB away from the speakers to minimize interference.
Route the LED through a hole in the speaker face of the enclosure and secure it with the LED holder. You may pull out one of the dust screen mounts and place it there.
Route the switches and jacks from the hole in the back and attach them to the plate and screw the plate in place on the back of the enclosure. Use hot glue on the crossover to put all the wires into the right position.
Connect the woofer and tweeter. Add the rubber feet to the bottom corners. Plug it in and test it!
If it works on wall power but not on battery, check the battery polarity and charge. Try to avoid reverse polarity on the battery as it is bad for the circuit. If it sounds bad, make sure you didn't get the woofer and tweeter wires mixed up. You might check to make sure terminal blocks have a good grip on the wires.