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How to Build an Audio Mixer

An audio mixer is an electronic circuit that combines audio signals from different sources, letting you adjust the relative loudness of each. It may have from two to 40 or more inputs, each with its own loudness knob. A device called an operational amplifier, or op amp, lies at the heart of the mixer. It adds the voltages from each input together and produces an output. Feeding the op is a set of potentiometers acting as volume faders for each input.

Things You'll Need

LM741 Op integrated circuit
Perfboard
4, 8-inch pieces of 22-gauge stranded, insulated hookup wire
5, 4-inch pieces of 22-gauge stranded, insulated hookup wire
3, 10K-ohm 1/4-watt resistors
2, 10K-ohm potentiometers, audio taper
15 to 30 watt soldering iron with fine tip
Electronics solder
10-volt bipolar DC power supply
3, RCA female audio connectors

Instructions

- 1
  Set the op integrated circuit into the holes in the perfboard. Make sure the pins go in straight and do not break or bend.
- 2
  Insert one lead of one of the 10K-ohm resistors into the perfboard hole nearest the IC̵7;s pin 6. The resistor itself should be on the same side as the IC. Insert the other resistor lead near pin 2.
- 3
  Insert one end of an 8-inch piece of 22-gauge wire near pin 2. Solder the connection between the wire, resistor lead and pin 2. Insert one end of another 8-inch wire near pin 6. Solder the connection between this wire, pin 6 and the resistor lead. Insert the end of a third 8-inch wire near pin 4 and solder the connection. Connect the wire̵7;s free end to the negative terminal of the 10-volt DC power supply. Insert the end of the fourth 8-inch wire near pin 7 and solder the connection. Connect the free end to the positive power supply terminal. Insert one end of three wires near pin 3 and solder the connection. Connect the free end of one of these three wires to the power supply ground terminal.
- 4
  Connect the free end of one of the two remaining wires at pin 3 to the ground solder lug of an RCA connector. Solder the connection. Connect the wire coming from pin 6 to the RCA connector̵7;s ̶0;hot̶1; solder lug. Solder the connection.
- 5
  Insert one lead of the second 10K-ohm resistor through the center solder lug of one potentiometer and solder the connection. Do the same for the third 10K-ohm resistor and second potentiometer. Carefully wrap about 1/2 inch of the free ends of the resistors together. On top of this connection, wrap the free end of the 8-inch wire connected to the IC̵7;s pin 2. Solder this connection.
- 6
  Insert one end of a 4-inch piece of wire through one end solder lug of one potentiometer and solder the connection. Insert the other end into the hot lug of an RCA connector. Solder the connection. Do the same with a second 4-inch piece of wire, the second potentiometer and the third RCA connector. Insert one end of a third 4-inch piece of wire through the ground lug of one of these two RCA connectors and solder. Insert the other end through the other RCA connector solder lug. Leave this connection unsoldered for now.
- 7
  Insert the end of a fourth 4-inch piece of wire into the unsoldered RCA ground lug connection and solder. Insert the free end of this wire into the remaining unused lug of a potentiometer. Insert one end of a fifth 4-inch piece of wire through the same solder lug and solder the two wires at this connection. Insert the free end of this wire through the remaining solder lug of the other potentiometer. Take the free end of the remaining unsoldered 8-inch wire at pin 3 and insert it into the solder lug of the potentiometer. Solder the two wires at this connection.

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