A resistor is a component in an electronic circuit that is used to create resistance. It achieves this by limiting the flow of electric current. If we compare electrical flow of energy to a water pipe, a resistor is like a tap that can limit the amount of water being moved through the pipe. Resistance in electronics is measured in Ohms (Ω). In audio circuits resistors are used for several reasons:
- To control current. This is can be for protection of the electronic circuits by for example reducing heat, and to divide current for different sections of the amplifier, or to create low current for amplification. For example, the reed bar on a Wurlitzer piano is high voltage (150VDC), but low current. The power amplifier section has lower voltage (25VDC), but higher current. Resistors help control this.
- Controlling gain. Resistors can be used to limit the amount of gain that in an amplifier. A simple example of this is a volume potentiometer. This has a maximum volume, which is limited by a resistor inside.
- Diverting voltage. Certain areas of the amplifier require lower voltage. Resistors can be used to split the voltage into different areas for what is needed for other components. For example, two resistors can divide the voltage by one resistor being put in the main signal pathway, and the other going to ground.
- Bias control. Bias is the term for making an amplifier work in the most efficient and effective way. The primary purpose of biasing is to elimiate distortion and unwanted noise in the amp. Resistors help achieve this by limiting the current send to a transistor so the transistor can amplify the signal correctly.
The most common resistor in electric pianos is a carbon film resistor. This has a lead at either end (axial), and has coloured bands on it to determine the resistance level, multiplier, tolerance, and coefficient. In Wurlitzer pianos, the majority of resistors are 1/2 watt. There are however other types of higher wattage resistors that are used. See below for their respective pages:
See Resistor (Ceramic)
See Potentiometer
Components that combine with resistors inside an amplifier include capacitors, transistors, and diodes.
