Use the Internet to search for and choose a bass headphone amplifier circuit schematic. Using symbols to represent electronic components and lines to represent how components are wired, a circuit schematic is the guide to construction. Most headphone amplifier schematics are compact and run on batteries.
Write down of all the different electronic components and their specifications, using the schematic. Purchase the necessary electronic components from electronics retailer. A bass headphone amplifier generally requires capacitors, resistors, transistors, on-off switch, battery socket, a potentiometer and audio pins.
Populate the protoboard with the electronic components by inserting the connecting pins of each component into the sockets. Arrange the electronic components in a layout that resembles the circuit schematic.
Turn the protoboard over, and begin wiring the electronic components according to the schematic. For connections more than one hole apart on the protoboard, use a small wire jumper. Insert the exposed copper tip of the jumper directly into the protoboard with the connection pin of the electronic component. Place the rosin-core solder against the joint of the wire and connection pin, and touch the heated tip of the 25-watt soldering iron to the solder. Melt a small amount of solder to the joint, and remove the soldering iron. For connections one hole apart on the protoboard, solder the pins directly together.
Drill four small holes into the project enclosure for the audio-in, audio-out, on-off and potentiometer. Remove the knob from the potentiometer, and then place the completed circuit into the project enclosure. Fit the nub of the potentiometer through the pre-drilled hole, and then re-attach the knob from the outside of the project enclosure.