How to Make a Speaker Amplifier

By David Sandoval

Audio amplifiers allow a small-signal audio device, such as an MP3 player, to be heard without the need for headphones. An audio amplifier must increase the audio signal without introducing distortion; however, to be practical, it must also be energy efficient. One type of amplifier circuit, the class AB amplifier, is capable of providing both high-fidelity signal reproduction and efficient amplification.

Things You'll Need

  • 12-volt battery
  • Audio plug
  • Bipolar junction transistors, one NPN and one PNP
  • Two 1-kiloohm resistors
  • Two 1N4007 rectifier diodes
  • Two 4.7-microfarad electrolytic capacitors
  • Electrical wire
  • Electrical pliers
  • Electronic solder
  • Soldering iron
  • Automotive speaker, 6 inch diameter

Step 1

Cut six 4-inch segments of electrical wire. Strip 1/2 inch of insulation from the ends of each wire segment.

Step 2

Twist together one end of the first wire jointly with the negative leads from the both capacitors. Touch the soldering iron to the twisted wire joint, and melt a small piece of solder on to the twisted wire pair. Smooth the solder along the joint so that the joint is flat and shiny (rather than dull and lumpy).

Step 3

Solder the loose end of the first wire to the "Tip" terminal on the audio plug. Solder one end of the second wire to the "Sleeve" terminal on the audio plug.

Step 4

Twist together one end of the third wire with one of the leads from the first resistor. Solder this twisted lead pair to the collector lead on the NPN transistor. Connect the loose end of the third wire to the positive terminal on the battery.

Step 5

Twist together the positive lead from the first capacitor, the anode lead from the first diode and the unoccupied end of the first resistor. Solder this electrical joint to the base lead on the NPN transistor.

Step 6

Twist together the anode lead of the second diode to the cathode lead on the first diode, and solder the electrical joint.

Step 7

Twist together the positive lead from the second capacitor, the cathode lead from the second diode and one of the leads from the second resistor. Solder this electrical joint to the base lead on the PNP transistor.

Step 8

Twist together the free lead from the second resistor with one end of the fourth wire. Solder this wire pair to the collector lead on the PNP transistor.

Step 9

Twist together the emitter leads from both transistors with one end of the fifth wire, and solder the connection. Solder the unoccupied end of the fifth wire with one of the speaker terminals.

Step 10

Solder one end of the sixth wire to the unoccupied speaker terminal. Connect the second, fourth and sixth wires to the negative terminal on the battery. Insert the audio plug into the output jack on the MP3 player or other audio device.