Download a schematic for a headphone amplifier from an Internet resource. A schematic represents audio components with symbols and how the components are wired with lines. Headphone amplifier circuits can be very complex and increased complexity means increased size. Consider portability when choosing your schematic.
Write down the electronic components represented in your schematic. Each symbol corresponds to an electronic component such as transistors, capacitors, resistors, audio jacks, or power switches. The number beneath the symbol represents the specifications of the component. Order the parts required for your circuit from an Internet resource.
Solder the components into the protoboard with a 25-watt soldering iron. Fit the connecting pins of each component through the holes of the protoboard. On the opposite side of the board, touch the rosin core solder to the joint of the board and the connecting pin. Melt a small amount of solder directly to the board by touching the tip of your heated 25-watt soldering iron to the solder. Allow the solder to cool for two minutes before clipping the excess connecting pin length with wire cutters.
Use a small amount of solder to wire the components together as represented in your schematic. Where the components are within one or two holes apart on the protoboard, a small amount of solder between the two components is sufficient. For electronic components farther than one or two holes, solder jumper wires between the components.
Add four small holes to your project enclosure with a small bit on your power drill. Unscrew the securing bolt from your audio switch, audio jacks, and volume knob, and place the components through the holes. Screw the securing bolts on each component from the outside of the enclosure. Enclose the internal components, including power supply, within the project enclosure.