Hello hello again ladies and gentlemen. Recently I came into a large speaker that I wanted to use for a sort of portable home stereo. To make this I turn to the ever popular Lm386 audio amplifier. By using a USB cord I can power if from a common place wall or computer adapter and by including a built in battery I can bring it on the go.
The output allows for switching between the speaker built with the amp or the Audio can be switched to connect to a pre-exsisting set of speakers. With The Lm386 chip and just a few discrete components one can build a loud little speaker for home use or use on the go.
Step 1: The Materials
To build this amp you will need:
-Lm386 audio amp circuit
-A 8 pin ic socket
-Two 220uf capacitors
-Two 100nf ceramic capacitors
-10 ohm resistor
-Two slide switches
-9 volt battery
-9 volt battery clip
-Female pin headers
-Male pin headers
-Acase (I chose an Altoids tin)
-A USB cord (I got mine from an old phone charger)
-And a USB power slupply
Step 2: The Tools
For this project you will need:
-Needle nose pliers
-A hot glue gun
-And a Rotary tool
Step 3: The Case
First begin by modifying the case. For this design i cut holes for the power supply to connect, the audio cord to go in, the two switches, The indicator led and the headers for the audio out port. Make a hole for the 9v battery clip and don't Forget make a hole for the pot like I did. He's very important and doesn't like to be left out
Step 4: The Circuit
To begin building the circuit cut off a bit of perf board to fit the case. The populate the circuit following the schmatic. Be sure to keep connections short and neat to prevent picking up radio signals and other noises. First add the socket to the center of the board followed by the 100nf cap between pin 8 and pin 3. Next is the 100nf cap between Pin 3 and a lead to the center pin of the pot. Add the output by connecting the positive lead of the 220uf cap to pin 5 of the IC. The add the high pass RC filter by connecting the 10 ohm resistor to pin 5 as well then to ground through the 4.7nf cap. Connect both pins 2 and 4 to ground as well as pin 6 to the VCC switch. Add the 220uf cap between power and ground this will keep yur circuit from getting too staticy.
I late found I had to bypass the 220uf cap on the output. I'm not sure why but it wouldn't work after I took it from the bread board to the perf board. If anyone knows why this is please let me know.
Step 5: Preparing the Hard Ware
The next step begins by adding the switch, the led, the pot, and the pin headers to the case. Hot glue them down and make sure they are snug in their place. Modify the power cord by cutting off the USB b end and extracting the leads. you may need to determine which ish positive and which is negative if it is not immediately evident. Take a length of speaker wire and strip the ends if yours is how mine is attach the lead marked with the white line to the center tip contact of the audio jack. Attach the unmarked lead to the outer ring contact.
Step 6: Wiring the Case.
to begin wiring the case bring the leads from the audio jack, the power slupply, the 9v battery clip and the speaker into the case. Connect the the negative lead of the led, the bottom contact of the pot, and one of the female pin headers legs to ground. Connect the unmarked lead from the audio jack, the negative lead from the power slupply, the negative lead from the battery clip and a lead from the speaker all to ground as well.
Next attach the positve lead from the batter clip to one lead of the power select switch. Connect the positve lead from the power slupply to the other contact of the power select switch leaving the center lead open. Connect one lead from the output switch to the open pin on the pin header. Connect the other open pin of the output switch to the open lead of the speaker.
Connect the remaining lead from the audio jack to the upper most lead of the potentiometer leaving the center pin open. This should be the lead with the white stripe. Lastly connect the positive leg of the led to the center pin of the power select switch trough the 1k resistor
Step 7: Adding the Circuit.
To add the circuit first place a few strips of electrical tape on the bottom of the board to prevent it from shorting out. Place the board in its new home and begin connecting the vcc lead to the center lead of the power select switch. Connect the ground lead to ground, connect the output to the output select, and connect the input to the center pin of the pot. it's very wise to put a bit of tape on the ground to keep it from shorting aswell.
Step 8: Closing It Up
The last step is to add a bit of hot glue to the leads exiting the case and hot gluing the case to the speaker. Then finally close up the case and test it out. The USB should provide ample amount of power to push the speakers and if you go out you can run it on battery power. Now you can enjoy your favorite music where ever you go and all for only a few dollars worth of parts and an afternoons effort.
Thank you and have a pleasant day.