Use the Internet to find and download a circuit schematic of a single-stage 300-watt amplifier. Schematics represent circuits and use symbols and lines to indicate components and wiring. Schematics also indicate necessary parts and how to connect the parts to form a working unit.
Write down each part listed and the specifications of that part as indicated on the schematic. Purchase the required parts. A 300-watt single stage amplifier requires at least ARF449A and ARF449B RF transistors for peak bass performance, high-voltage capacitors that compress and filter the signal, various inductors, single-gate transistors, a heat sink to keep the circuit from overheating and fixed resistors.
Use a wax pencil to mark the place on the blank circuit board where each electronic component goes, according to the schematic. Place each electronic component in its marked space, and either bend the connecting pins to attach the parts to the board or screw or glue them in place as necessary.
Solder each component in place with a 25-watt soldering iron and rosin-core solder. Place the rosin-core solder against the joint of the electronic components connecting pin and the circuit board. Touch the heated tip of the soldering iron to the solder, and melt a small amount of solder directly onto the joint. Snip the excess connection pin length off with wire cutters after the solder cools.
Use a wax pencil to draw the wiring between electronic components as represented in the schematic. Follow the drawn, from left to right, lines with a wiring pencil, which draws a small amount of conductive molten copper directly onto the circuit board.
Modify the project enclosure with a hand-held rotary tool to account for external components, such as audio-in and audio-out connections and heat sink. Two holes for audio-in and out and several slits for heat sink exhaust are sufficient, but schematics may vary. Enclose the 300-watt single stage amplifier circuit in the project enclosure and screw shut.