DIY: Audio Amplifier 300 Watt Single Stage

Written by jason parnell
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DIY: Audio Amplifier 300 Watt Single Stage
Building a 300-watt amplifier can be completed in a day. (circuit board image by mite from

A 300-watt single stage amplifier commonly is used to amplify low, or bass, frequencies. This type of amplifier efficiently processes and amplifies the 80hz range, where listeners find the "boom" of a bass drum sound. Efficient amplification is important because the better an amplifier is at containing the signal-to-noise ratio during amplification, the less noise and more signal listeners hear after amplification. A 300-watt single stage amplifier is a project users can build in a day.

Skill level:

Things you need

  • Blank circuit board
  • 25-watt soldering iron
  • Rosin-core solder
  • Wiring pencil
  • Wire cutters
  • Metal project enclosure
  • Screwdriver
  • Glue
  • Handheld rotary tool
  • ARF449A and ARF449B RF transistors
  • High-voltage capacitors
  • Capacitors
  • Air-core inductors
  • Iron-core inductors
  • Single Gate transistors
  • Fixed resistors
  • Heat sink

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  1. 1

    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.

  2. 2

    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.

  3. 3

    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.

  4. 4

    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.

  5. 5

    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.

  6. 6

    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.

Tips and warnings

  • If building an amplifier for a car, consider customising the size and shape to best complement the audio system.
  • Redraw the schematic, substituting actual pictures of the listed parts for the symbols, if experiencing difficulty reading and following the schematic.
  • A 300-watt audio amplifier is a high-voltage unit and should never be used outside of the project enclosure.
  • Always use soldering irons and wiring pencils in a well-ventilated area.
  • Always wear eye protection when using molten metal.

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