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Portable Phone Speaker

This two watt portable phone speaker was made as a christmas present for my nephew. It uses a LM380 amplifier chip and some other basic components. It's not hard to build and the result is a powerful and practical custom speaker that's compatible with any device that can output audio to a 3.5mm jack.

Finished Speaker

I made a short video on what's involved in building the speaker.

Parts list:

  • Enclosure - Home theatre speakers make convenient enclosures, just make sure there's enough room for the electronics in the back. I made mine from some scrap MDF.
  • Speaker Driver - I used one salvaged from a broken home theatre speaker.
  • Amp and Supporting Components - Capable of being powered by a battery. This article uses the LM380 amplifier IC but the LM386 is also a popular choice. Supporting components include a power toggle switch, audio cable with 3.5mm male jack, power indicator LED and 360 ohm resistor (optional) and 10k volume potentiometer (optional). A pre-assembled amp from any online retailer is an alternative to building one.
  • Battery - The previously mentioned amps both run from a 9v battery. These don't have a great capacity so AA or AAA batteries will make the tunes last longer.

While scavenging through some old parts I found two LM380's. After googling around a bit, I found a popular LM380 circuit and assembled it on a breadboard. It sounded decent.

Breadboarded Circuit

It needed a real test, so I knocked one together on some proto board and installed it in the back of an old sony home theatre speaker. The end result sounded decent. The audio control pot was ditched in favour of controlling the volume through the phone. I wired the power to the speaker terminals and threaded the 3.5mm jack through the stand mount.

Phone Speaker

Christmas was coming up and my nephew is always listening to music or playing games on his phone. It would make a nice gift if I coupled this simple design with a slick custom case.

Basic Box

The enclosure is nothing fancy, just MDF squares glued and clamped into a box shape. I recessed the area in the front panel where the speaker driver installs with my dremel for extra swankyness. You will need a hole for the audio cable and three mounting holes for the power switch, power LED and volume pot. 

Filler Applied and Sanded

After plenty of sanding and a bit of wood filler the box had nice curves and smooth edges, just needed a few coats of primer.

A Few Coats of Primer

A small amp is required for this project, you can easily grab a pre-assembled or kit amp from eBay which is handy if you want to save some time or you're not comfortable reading schematics.

Pre-assembled Amp

Alternatively, you can assemble the amp I've shown based on the LM380. The LM386 is also a very popular half watt amp with many circuits available online to play around with. As there's only one speaker driver in this build, a mono amp will suffice. Any amp will at least have an input where the audio cable from the phone connects, a power connection and an output that sends the amplified signal to the speaker. Most will also have a volume control pot. Check the datasheet or documentation to determine the specifics for your amp.

Image source http://electronicszone.net46.net/sites/default/files/lm380%20amplifier.bmp

I used the schematic above but added a power led with 360 ohm resistor to indicate when the device is switched on. This instructable does a good job of explaining how to put one together. I'll include the volume control pot too, the first speaker would start to distort at 2/3 iphone volume as the amp was always set to max volume without it. This is a simple circuit so you can just assemble it on some proto board.

Installed Amp

I've been experimenting with making my own PCB's using the toner transfer method so I'll get some more practice. There's plenty of tutorials and resources available for this online so I'll just explain briefly.

Board Design

The circuit board is designed using CAD software (shown above. Designed in cadsoft eagle) and printed onto shiny photo paper. This print out is then transferred to the board with an iron.

Board and Etching Solution

The board is then placed in an etching solution. I used one part hydrogen peroxide, one part hydrochloric acid as these chemicals are easy to obtain in Australia. This solution eats away the uncovered copper leaving an etched board, just drill out the holes and install the components.

Etched Circuit Board

Once all the amp parts are installed on the board, the additional components were connected for a final test before installation.

Assembed Amplifier

Connecting it all up is pretty simple, the audio cable connects to the input. Strip the audio cable and combine the postive connections from the left and right channels as we don't need stereo output.

3.5mm Jack /w Stripped Cable

If you have a kit amp, you may need to desolder the volume control pot and extend its connections. Stuff it all in the enclosure. A little bit of hot glue to keep things in place never hurts. The face of this speaker sticks on with velcro tabs so you can access the batteries.

Components Connected

Although the LM380 seemed to run well off a 9v battery, the datasheet recommends a minimum 10v power supply. I ended up using 7 x AAA batteries in series as these will power the speaker for a lot longer and meet the 10v minimum requirement.

Completed

I pumped some tunes through it for a couple of hours as a final test to make sure all is well. It worked a treat and my nephew was happy with it. I originally wanted to keep the body of the unit matt white however this isn't a very durable finish so I did the whole thing in a satin black.

Black Finish

The other speaker sits on my bedside table and is powered using a 9v .21A power pack from an old cordless phone charging dock.

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