How to Build a Voltage Divider Bias Circuit With Volume Control

Voltage dividers, two resistors connected in series, are at the heart of volume control circuits. You can find these circuits in everything from music players to televisions. In a typical volume control circuit, one of the resistors is a variable one -- its value controlled with a knob. When this output voltage is buffered with an op amp, the value of the variable resistor can be used to directly bias the voltage at the input of the amp. This enables you to set the gain of the circuit, so that you can control the volume of your audio signal.

Things You'll Need

  • Electronic breadboard
  • Breadboard wire jumpers
  • Op amp
  • 5,000-ohm resistor
  • 10,000-ohm variable resistor
  • Power supply (dual, +/- 15 volts)
  • Signal generator (sine wave 1 to 20,000 Hertz)
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Instructions

    • 1

      Insert the op amp into your breadboard. Wire the op amp's positive power supply pin to the power bus of the breadboard. Wire the op amp's negative power supply pin to the negative power bus of the breadboard.

    • 2

      Insert the 5,000-ohm resistor in the breadboard. Wire one end of this resistor to the op amp's positive input signal pin. Wire the other end to the breadboard's input signal bus.

    • 3

      Insert the 10,000-ohm variable resistor into the breadboard. Wire one end of this variable resistor to the op amp's positive input pin. Wire the other end to the breadboard's ground bus.

    • 4

      Wire the op amp's output pin to the op amp's negative input pin.

    • 5

      Connect the power supply's positive terminal to the breadboard' positive power supply bus. Then connect the power supply's negative terminal lead to the breadboard's negative power supply bus. And connect the power supply's ground lead to the breadboard's ground bus.

    • 6

      Connect the signal generator's positive terminal to the breadboard's input signal bus. Then connect the signal generator's negative terminal to the breadboard's ground bus. And connect a speaker load between the output pin of the op amp and ground.

    • 7

      Apply power to your circuit, and turn on the signal generator. Vary the signal generator's frequency between 10,000 and 11,000 Hertz. Adjust the variable resistor control knob, to adjust the amplifier gain. Observe that the speaker's volume increases or decreases, depending on the way you turn the turn the variable resistor's knob.

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