Advantages Of Direct Constant Voltage Operation In Power Amplifiers

A good practice widely used by power companies has been applied to audio engineering. Power companies are known to minimize resistive power losses by using high voltage and low current when delivering power over miles of cable. They do this by deploying Constant Voltage Transformer(CVT) at the power station and step-down transformers at each customer location. This configuration reduces power losses due to I2R heating of the power cables.

The same solution can be used for audio communications in the form of a constant voltage system (usually 70 volts). Such a system is commonly used when a single amplifier drives multiple speakers over long cables (over 50 feet). Examples include distributed speaker systems for portable sound reinforcement, paging, or low SPL background music.

What is constant voltage? “Constant voltage” is often confusing because the voltage in audio programs is not actually constant. A more accurate term would be “high voltage.”

Figure 1 shows a typical high voltage system. A transformer at the output of the amplifier steps up the voltage to about 70 volts at full power. At each speaker, there is a step-down transformer that matches the 70 volt line to the impedance of each speaker. The primary circuits of all constant voltage transformers are connected in parallel to the secondary circuits of the transformers of the power amplifier.