How Does a Guitar Amplifier Work?

• As an electric guitar is played, the metal strings vibrate and create an electromagnetic field near the guitar pickups. This electromagnetic field is translated by the pickups into an electrical signal, and transmitted through the electronics in the guitar to the guitar amplifier.
  
  An electrical circuit in an amplifier receives the electrical signal and reproduces it at a higher voltage and current setting. This new, amplified electrical signal is then applied to a large speaker, and is converted into mechanical waves that our ears can hear. The higher the voltage, the louder the signal.
  
  

Creating an Amplifier at Home

• Many of the parts needed to create a guitar amplifier can be found at an electronics store (such as Radio Shack). To create a simple amplifier, you will need the following items:
  
  Speaker cable
  Soldering iron and solder
  One female phono plug
  An operational amplifier (also known as an "op-amp," such as the National Semiconductor LM1875)
  One potentiometer
  One electrical resistor
  Speaker
  Small electrical switch
  DC power supply (No more than 60V; 12V recommended for a low-power application)
  
  Cut about 6 inches of speaker cable, and strip both ends of approximately half an inch of insulation. On one end of the speaker cable, solder one of the wires to connect electrically to the center connector of the female phono plug. Solder the other wire to connect to the "shield" (outer) connector of the phono plug.
  
  With the other end of the speaker cable, solder the wire that connects electrically to the center connector of the phono plug to the "+ In" connector on the op amp. (On the LM1875, this is pin 1.) Solder the other end to connect electrically with the negative terminal of the DC power supply. Solder the electrical resistor, one end to connect with the "- In" connector on the op amp (pin 2 on the LM1875), with the other end of the resistor soldered to the negative terminal of the DC power supply.
  
  Take a second piece of speaker cable (about 3 inches) and strip it of approximately a half-inch of insulation on each side. Pull the two wires apart completely. Use one of the wires to connect the wiper connection on the potentiometer to the Output connection on the op amp (pin 4 on the LM1875). Solder the wire to the wiper terminal, and solder the other end of the wire to the output connection.
  
  Using the other stripped wire, solder one end to one of the potentiometer's fixed contact terminals. Solder the other end jointly to the "- In" connector on the op amp, and the resistor that is connected to the "- In" connector.
  
  Cut another 3-inch piece of speaker cable, and strip the wires of a half-inch of insulation. Pull the wires apart. Take the speaker, and solder one of the electrical connections to one of these wires. Solder the other end of this wire to the negative terminal of the power supply. Take the other wire, and solder one end to the "Output" pin of the op amp, and solder the other end to the other electrical connection on the speaker.
  
  Take a 6-inch piece of speaker wire, and strip it of a half-inch of insulation. Pull the wires apart. Taking one wire, solder the "Vcc" pin on the op amp (pin 5 on the LM1875) to one end of it, and to the other end, solder it to the positive terminal on the DC power supply. Take the other wire, and solder one end to the "V EE"pin (pin 4 on the LM1875), and solder the other end to the negative terminal of the DC power supply.