How to Build Your Own Active Speaker for the PC

The amplifier receives its power from a power adapter.

Active speakers (also known as powered speakers) amplify the output audio signal from a computer's sound card. An active speaker uses an external power source (such as a battery pack or a DC power adapter) to drive the amplification circuit.

Things You'll Need

• One 12V DC adapter
• Electrical pliers
• Electrical wire
• Soldering iron
• Electronic solder
• Dual operational amplifier microchip (such as an LM158)
• Two 1 Kilo-Ohm resistors
• Two 10 Kilo-Ohm resistors
• Wired headphones
• Two 8 Ohm speakers

Instructions

1. 

   DC adaptor wires are marked as to polarity.

   Snip the tip off the DC adapter. Pull the wire ends apart until there is at least six inches between the wire ends of the adapter. Strip 1/2 inch of insulation off each wire end. Solder the positive wire to the "V+" operational amplifier pin.

2. Cut eight lengths of wire and strip 1/2 inch of insulation from the ends of each wire. Solder one end of the first wire to one of the terminals on the first speaker. Solder one end of the second wire to the remaining terminal on the first speaker. Solder one end of the third wire to one of the terminals on the second speaker. Solder one end of the fourth wire to the remaining speaker terminal. Twist together the free ends of the second and fourth wires with one end of the fifth wire, and solder the connection.

3. Twist the free end of the first wire together with one of the leads on the first 10 Kilo-Ohm resistor. Solder this twisted wire pair to the "Output A" pin on the operational amplifier chip. Twist together the free end of the third wire with one of the leads on the second 10 Kilo-Ohm resistor. Solder this twisted wire pair to the "Output B" pin on the operational amplifier chip.

4. Snip the headphones off the headphone cable. Strip 1/2 inch of insulation from each of the cable wires at the snipped end. Solder the red wire to the "non-inverting input A" on the operational amplifier microchip. Solder the white wire to the "non-inverting input B" on the operational amplifier microchip. Twist together both black wires with one end of the sixth wire, and solder the electrical connection.

5. Twist together the free lead from the first 10 Kilo-Ohm resistor jointly with one of the leads from the first 1 Kilo-Ohm resistor, and with the "inverting input A" terminal on the operational amplifier microchip. Solder the electrical connection. Twist together the free lead from the second 10 Kilo-Ohm resistor jointly with one of the leads from the second 1 Kilo-Ohm resistor, and with the "inverting input B" terminal on the operational amplifier microchip. Solder the electrical connection.

6. Solder one end of the seventh wire to the "GND" connection on the operational amplifier microchip. Twist together the free leads of the 1 Kilo-Ohm resistors jointly with one end of the eighth wire, and solder the connection.

7. Twist together the negative power supply wire jointly with the free ends of the fifth, sixth, seventh and eighth wires, and solder the connection.

References

• Georgia State University: Op-Amp Varieties
• National Semiconductor: LM158/LM258/LM358/LM2904 Low Power Dual Operational Amplifiers