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How to Build an Amplified Microphone

A microphone is an electromechanical device which converts sound waves into an audio AC signal. This signal is normally too small to drive a loudspeaker or other audio device; therefore, the signal from a microphone must be amplified before it can be reconverted into sound waves. One way to accomplish this amplification is to wire an amplifier to the microphone.

Since audio signals are susceptible to distortion, it is important to use an amplifier that will not introduce distortion during amplification. Many amplifier circuits use a solid-state solution called an operational amplifier integrated circuit, or "op-amp" for short.

Things You'll Need

Microphone with attached cable
Electrical wire
Electrical pliers
Electronic solder
Soldering iron
LM158 Operational Amplifier
100-kiloohm resistor
100-ohm resistor
Battery snap connector
9-volt battery

Instructions

- 1
  Cut the microphone cable approximately four inches away from where the cable connects to the microphone base. Strip half an inch of insulating material away from the wires at each end of the microphone cable. There will be two wires running through the microphone cable. Note the colors of the microphone cable wires; a wire that is red or white indicates a positive wire. A black or green wire indicates a negative wire.
- 2
  Twist together the positive cable connected to the microphone plug with one of the leads from the 100-kiloohm resistor. Solder this connection together with the output terminal (pin 1) on the op-amp.
- 3
  Twist together the free lead from the 100-kiloohm resistor together with one of the leads from the 100-ohm resistor. Solder this twisted wire pair to the inverting input terminal (pin 2) on the op-amp.
- 4
  Solder the positive wire from the cable connected to the microphone together with the non-inverting input terminal (pin 3) on the op-amp.
- 5
  Solder the red wire from the battery snap connector to the "V+" terminal (pin 8) on the op-amp.
- 6
  Cut four pieces of electrical wire, each four inches long. Strip a 1/2 inch of insulating material from the ends of each wire segment.
- 7
  Twist together one end of the first wire segment with the negative wire from the cable connected to the microphone. Solder this electrical joint.
- 8
  Twist together one end of the second wire segment with the negative wire from the cable connected to the microphone plug. Solder this electrical joint.
- 9
  Solder one end of the third wire to the "GND" terminal (pin 4) on the op-amp.
- 10
  Twist together one end of the fourth wire to the unoccupied lead from the 100-ohm resistor, and solder this joint.
- 11
  Twist together the loose ends of the first, second, third, and fourth wires with the black wire from the battery snap connector, and solder the electrical joint.
- 12
  Plug the battery into the battery snap connector.

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