How to Amplify an Audio Signal With a Non-OP Amp

A transistor is the foundation of a Class A amplifier circuit.

Audio signals require amplification before they can drive an audio speaker. Since audio signals require exact waveform transmission from one side of an amplifier to another, it is critical to choose an amplification method that will keep signal distortion to a minimum.

Operational amplifiers (or, "op-amps" for short) are complex integrated circuits that you can use as the basis for an audio amplifier. If there is no op-amp available, you can employ the Class A amplifier, another low-distortion amplification method .

Things You'll Need

• One 12 Volt DC power supply
• One bipolar junction (NPN) transistor
• One 1MΩ resistor
• One 720kΩ resistor
• One 360kΩ resistor
• One 0.47 μF dielectric (non-polarized) capacitor
• Two ring terminals
• Electric wire
• Electric pliers
• Soldering iron
• Electronic (rosin core) solder

Instructions

1. Cut four lengths of wire, and strip ½ inch of insulation off the ends of each wire. Slip the first ring terminal over one of the ends of the first wire, and solder the terminal to the wire. Using the pliers, twist the free end of the first wire to one of the capacitor leads, and solder the joint. Twist together the free capacitor lead jointly to the transistor base lead and to one of the leads on the 1MΩ resistor. Solder this electrical joint as well.

2. Twist one of the leads from the 720kΩ resistor jointly to one end of the second wire and to the transistor collector lead. Solder this connection. Slip the remaining ring terminal over the free end of the second wire, and solder the terminal to the wire.

3. Twist one of the leads on the 360kΩ resistor together with the transistor emitter lead, and solder the connection. Twist together the free leads of the 360kΩ resistor and the 1MΩ resistor jointly to one end of the third wire, and solder the connection. Twist together the free lead on the 720kΩ resistor and one end of the fourth wire. Solder this connection.

4. Attach the free end of the fourth wire to the positive terminal on the power supply. Attach the free end of the third wire to the negative terminal on the power supply.

Tips & Warnings

• The audio input signal must be connected to the ring terminal at the end of the first wire. The audio output device must be connected to the ring terminal at the end of the second wire.

• Class A amplifiers are inverting amplifiers, so the resulting output signal will be an amplified mirror image of the input signal.

References

• Electronic Devices; Thomas Floyd; 1996
• Elliot Sound Products: Simple Class A Amplifer