In this Instructable I will show you how to build an audio amplifier out of mostly recycled parts!
To do this project, you should have some experience in working with power tools, soldering and electronics in general.
I will help you as much as I can if you stumble upon a problem, just post it in the comments.
I thought of this project while clearing out my junk box. I thought it would be useful to have a
small portable speaker to, for example, take with camping.
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Step 1: What You Need
To make the box:
- a metal or plastic box big enough to mount your speaker on (I used an old tin box from a trading card game)
- a dremel or other rotary cutting tool
- a drill
- ( sanding paper (optional)) See Step #4
- ( spray paint(optional)) See Step #4
- a speaker (should be an 8ohm speaker; I got mine from an old TV) If your speaker can me mounted on to the tin with bolts, you need these, otherwise you could use hot glue or other methods.
- A female audio connector AND a male-to-male audio connectot OR just a male audio connector SEE STEP #5
- All parts you need for your amplifier circuit SEE STEP #7
- Female and male header pins (see why in Step #7)
- Electrical tape or other means of insulation
- a DPDT toggle switch (if you don't know what I mean, check out Step 6 and perhaps http://en.wikipedia.org/wiki/Switch#Contact_terminology
Step 2: Cutting the Hole for the Speaker
First, take the lid from your box and use your rotary cutting tool to cut a hole into the lid, so that the speaker fits right in . Make sure to mark the mounting holes of your speaker if it has any.
Step 3: Drilling the Holes for the Bolts
If your speaker can be mounted with bolts, you should drill the holes into the box for them now.
After drilling, check to see if you alligned the holes right (see pic #3).
Step 4: Optional: Sanding and Painting the Box
If you would like to paint your box, like me, you should first roughen the surface with sandpaper (see pics #5 & #6) and then paint your box, I used spray paint (see pic #4).
After painting (see pic #1 & #2) you can mount your speaker (see pic #3) but be prepared to take it off again.
Step 5: Adding the Audio Plug
For your amp to play anything it must be able to recieve something.
So pick a spot on your box and drill a hole for your plug (see pic #2).
Before mounting your plug, you should connect both stereo inputs (see pic #3) and perhaps insulate the connections (see pic #4).
Then, mount your plug (see pics #1,#5,#6).
WARNING: If you don't have a male-to-male audio connector (see pic #7) and can't make one you should use a male audio connector instead of a female connector. NOTE THAT having a female and a male-to-male connector looks better because you don't have anything sticking out the side of your speaker box but it's up to you.
Step 6: Attaching the On/off Switch (DPDT)
So that your amp can be turned on and off, you'll need to add a DPDT (double-pole double throw) toggle switch to your amp.
Just like when you mounted the audio plug, you'll need to mark,drill and fasten the switch.
Before drilling, I took off the speaker for convenience.
Step 7: Making the Amp Circuit
Now is the time to make your amp circuit. You can take pretty much any audio amplifier Integrated Circuit (IC).
I took the LM1877 because I had it laying around. I could have also taken the LM380 or the LM386.
If you want to know if the IC you have is an amp, just search its number(or name) on the search engine
of your choice and take a look at its data sheet. That's also where you'll find the schematic for your amp.
I strongly suggest to test the circuit on a breadboard before soldering it to a circuit board.
NOTE: You can see on the pictures that I used female header connectors for power, audio IN and audio OUT.
This is optional; you can also just solder the wires from the battery and audio plugs directly to the circuit board
but if you do that, you should first look at the following steps to make sure you get everything right.
I strongly suggest to use header pins like I did, because with them you can, for example,
switch out amp circuits to compare their sound quality or take out the circuit to repair or change it.
It can save you lots of pain!
WARNING: Pay attention to the voltage your amp IC can handle. DON'T EVER apply more voltage to
it than it can handle. ALSO make sure your capacitors can handle more than the max voltage of your amp IC.
If you keep this warning in mind you can avoid replacing lots of parts.
If you're using the LM1877 you can check out its schematic at pic #6 . You'll find many other amp circuits that have a similar shematic. I got this schematic from http://www.national.com/mpf/LM/LM1877.html#Overview .
Note: In case you're wondering why I used a stereo amplifier IC, it's because I might want to use it for other projects.
For this project I will only be using one output.
Step 8: Finishing the Speaker
After making your amp circuit, go on by soldering two wires to your speaker, each about 20cm/8inches long, and attaching male header pins to them.
Step 9: Adding the Power
Now add the power to your amp: Depending on the max voltage of your IC you can attach 9V-18V to your amp, perhaps more.
For the LM1877 with a max voltage of 24V I chose two 9V batteries to power my amp.
Make sure to solder the wires from the batteries first to the on/off switch and then to the amp circuit so that you can turn it on and off.
You can see on pic #6 that I attached both positive and negative wires to the switch. You'll perhaps find that not necessary, but if you do it my way you don't have to change anything in case to want to go beyond Step 11.
Step 10: Hooking Up Everything
Lastly, connect all header pins to the circuit board. Watch for polarity!
Step 11: FINISHED!!!
Now calm down and check if everything is connected the right way around and make sure the batteries are inserted.
Now plug in your music source and turn your speaker on. If you get loud music and not too much background noise,
you are victorious!
If you don't hear squat, immediatly turn it off and follow these few, simple steps:
- Did you really plug in everything? Check that.
- Take out your circuit. Take 5 minutes of your precious time to compare every connection of your circuit with those of the schematic.
- If your problem is still there AND you used a stereo amplifier IC, a possible solution would be to switch the Left and Right audio outputs like in pic #2. A perhaps simpler solution would be to just connect both outputs because you only have 1 speaker anyway (see pic #3). I had that problem.
- Problem still not solved? Post a comment, I'll do my best.
Final note: If you're asking which of my parts I used for my speaker box were recycled, then here you go:
- The speaker, the bolts and nuts to mount the speaker, the capacitors and 4 of the 6 resistors in my amp circuit were salvaged from an old TV
- The tin box itself was a collectible tin from a trading card game
- The amp IC was in my box of "useless ICs" which I would have cleared out some day
Step 12: More?
- Add a volume control
Add a plug for external power
- Add a mute button (?)
- Add a LED to show the speaker box is on
In this add-on I show you how to add an external power source so your batteries don't go emty as fast!
I will add more add-ons as soon as I can . For now, you can follow me, rate and comment and perhaps give me ideas for more features to add to the speaker box!
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