Transformers are used to transfer electric current from one circuit to another without having physical contact between them. Audio transformers are specially designed transformers for using audio circuits. Similar to any other transformer, Audio transformers also have a primary winding and secondary winding. The primary winding acts as the input section of the transformer and secondary winding acts as the output. The input part will take an AC signal (usually an audio signal) as input to produce an AC output without any distortions.
The transformer is constructed by winding insulated wire coils around a magnetic core. When the primary winding receives a signal, a magnetic field is created which will result in the production of a signal in the secondary winding. The magnetic field produced will be proportional to the applied input voltage. Higher the input voltage, the higher will be the intensity of the magnetic field created and higher will be the output voltage. An audio transformer will only pass alternating signals because only alternating current can create a varying magnetic field which is required to generate a current in the secondary winding. If a DC signal is applied to the input, varying magnetic field will not be created and the signal will not be passed to the output.
The transformer can either be step up, step down or unity 1:1. If the number of turns in the primary winding is less than the number of windings in secondary, then it is a step-up transformer. If the number of turns in primary is greater than that of the secondary winding, then it is a step-down transformer. If the number of turns in both primary and secondary windings are the same, then it is called a unity 1:1 transformer. The input signal given to the unity transformer will reach its output sections without having any changes in the signal wave.
Audio transformers work at a signal frequency range of 20 Hz to 20 kHz which is commonly known as the audio frequency range.
Advantages and applications
Audio transformers are used to increase or decrease the voltage of an audio signal. Audio devices like microphones can make this feature useful because the electric signal generated by such devices is very small. Many audio instruments like mixers, amplifiers and other sound equipment use audio transformers because they help to reduce noise, manage signals and acts as a bridge between two devices.
Audio transformers have the ability to block incoming DC signal from passing to output. Unity 1:1 transformer is used for this purpose because the input and output voltages are the same. No modifications will be made to the input. This DC blocking feature is helpful for audio recording devices.
The impedance of audio speakers and impedance of transformers will be different usually. For transferring maximum power, attaining great audio fidelity and power efficiency, the impedance should be matched to each other. Since audio transformers can change the impedance value, they are used for impedance matching and electrical isolation purposes also. If the impedance is mismatched, the sound will be distorted and weak.