To connect the amp to the Raspberry Pi 2, we'll need two wires. Cut two pieces of 30AWG wires to about 10cm in length. Strip and tin the tips of each wire.
On the bottom of the Raspberry Pi 2 PCB, locate the audio jack and inspect the three pin connected to the component.
Take note of the two circles highlighting the pins. The left pin (blue) will connect to the negative pin on the amp, while the right pin (red) connects to the positive pin. The middle pin does not need to be tinned (disregard the tinning in the photo).
Place the tip of the soldering iron over the pin and apply a small amount of solder. This will make connecting wires to the audio amp much easier.
Solder the new wires to the pins on the bottom of the Raspberry Pi. The negative(blue) wire connects to the left pin, while the positive(ed) wire connects to the right pin.
Solder the negative (blue) wire to the A– pin on the amp, and the positive (red) wire to the A+ pin on the amp.