This is a small powered amplifier that plugs into a 1/8" stereo jack and accepts the same. Many people know nothing about amplifier circuits and would have no idea how to make one, so why don't we let a company make the circuit, and then just tweak it to meet our needs (So admittedly one does need to know a little about electrical circuits, speakers, and soldering).

This is the perfect thing to provide the extra energy needed to power larger speakers with a portable audio device without severely draining battery power. This pocket amp also allows for louder audio through headphones or small speakers. Time to blow out those voice coils!

Step 1: Hunt and Gather Supplies

For this project you will need:
-A small hearing amplifier, often called a personal amplifier or advertised as spy hearing (I used a
Radioshack brand "amplified listener" )
- Stereo headphone cable with 1/8" jack
-Screwdriver
-Solder
-Soldering iron
-2X AAA batteries (or whatever your particular model requires)
Not shown
-Connecting wire, scrap wire
-Electrical tape
-Hot glue, silicone or epoxy
-Drill and bit slightly larger than the the width of your headphone cable
-Audio source and headphones to check your progress.

Step 2: Void the Warranty

Using a screwdriver, unscrew all the necessary screws and pry the case open, remove the battery cover and get rid of any shielding (this does reduce audio quality but we need that space for some wires.)

Step 3: Check the Microphones

Identify what parts are which and what wires go where. You will need to remove the microphones and use the wires leading to them as your input source

Step 4: Identiy Your Connections

After severing your left and right microphones, mark which connections go with which microphone: left or right.

Step 5: Wire the Connections

Since someone else made the circuit, all we care about are the input and outputs, the output is already wired as a 1/8" headphone jack, and by soldering together the leads to the (now removed) microphones, red to red and black to black, we can then wire the circuit to our own input source

Here some of the wires attached to the board were too short, so I used a piece of scrap wire (yellow) to connect them.

Step 6: Strip Your Headphone Cable and Solder

Solder the red wire from your headphone cable to the combined red cables soldered to the amp circuit, and then do the same with the black wire (in my case white). the third wire may require some tweaking: put the batteries in, turn on the amp and plug some headphones or speakers into the jack. Then with the volume set low, plug an audio source into the headphone cable and listen to some music. Touch the third wire (in my case, bare copper) to different points around the circuit, then solder it to the one that makes the music sound the best. In my case it was where the black wire from the batteries was soldered to the headphone input.

Step 7: Tape

Put a tiny piece of electrical tape over any bare connections or bare wire, this will prevent short circuiting when you put it all back together.

Step 8: Exit Strategy

Drill a hole the same diameter as your headphone cable in the case of the amplifier, now all your wiring will have a way out of the box.

Step 9: Reseal and Enjoy.

lay down all the wiring and replace the cover. Then seal any gaps with the hot glue. I prefer hot glue over epoxy or other serious glues, because I can easily get back inside the case in case I need to make repairs.

Step 10: Why?

This was actually a sub-project in a larger project that had many components. I needed to make an amplifier so that I could provide two speakers (a 6.5" woofer and a public address horn) with enough power to produce a decent volume without draining the batteries from my iPod. I needed some kind of powered amplifier so that the speakers would draw power from the amp rather than the iPod; However, I needed the amp to be battery powered and small enough to be hidden in a breast pocket of a suit. I found a "amplified listener" at Radioshack and realized that it's essentially an amplifier circuit with a battery pack, all that needed to change was the input source.

The full project which I have just finished with the completion of the pocket amplifier took me over six months to make. "Max Treble" is a standalone speaker system and iPod dock.

The amp fits perfectly in his breast pocket.