What is the working principle and structure of an audio transformer？

Although an Audio transformer does not have a physical connection between his primary and secondary coil, the transformer provide bidirectional feature between this two windings. We can also use the same primary side as secondary and secondary as primary. In such case, the transformer provides signal loss in one direction and signal gain in reverse direction or vice versa.

The audio transformer works at frequencies between 20 Hz to 20 kHz. So, the operation of an Audio transformer has much wider frequency range.

As discussed above, the audio transformer uses Impedance balancing technique. It is very useful for balancing amplifiers and loads (Loudspeaker and other) that use a different input or output impedances for maximum power transfer application.

In modern days, speakers impedances ranges from 4 to 16 ohms, typically 4 ohms, 8 ohms or 16 ohms speakers are available whereas Transistor or Solid state amplifiers use 200 – 300 ohms output impedance. If the amplifier is a retro design, such as old Valve or Tube amplifier then the output voltage sometimes reach 300V with 3k impedance. We need impedance matching transformer which will convert the High impedance to low impedance and should convert the voltage and current to a level which will directly drive a loudspeaker.

A Transformer can have multiple windings in the primary and secondary side. The ratio between primary and secondary windings, the number of coils turns in the primary side (Np) and a number of coil turns in secondary (Ns) is called the turns ratio. This turns ratio also defines the primary and secondary voltage ratio as the voltage is directly proportional to the primary and secondary winding turns.

So, NP/NS = VP/VS

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