15/02/2022

Microphone Transformer

 

Microphone Cable

  • The audio transformer can be used for matching microphone to input of amplifier. 
  • The main function of the microphone transformer is to matching impedance between microphones, connecting cables and amplifier input.
  •  It should be noted that there is no signal reduction during impedance mismatching.
  • Figure shows long microphone cable consists of two conductors twisted together which are surrounded by conducting metal foil or braid. 
  • As two conductors are twisted, magnetic fields generated by each conductor tends to cancel out. 
  • The earthed conducting foil protects conductor from external magnetic field.



microphone-transformer.png


microphone-cable.png

  • A microphone is connected to cable through single primary winding and center taped secondary winding transformer. 
  • As cable is fed from a center taped transformer, signals on two conductors are in antiphase.
  • The difference between two input signals applies at the amplifier input, the output signal is doubled in amplitude. 
  • Any noise at the input signal cancel out automatically because two conductors are twisted  each other in the opposite direction. 
  • The combination of signal at the amplifier can be carried out either by differential amplifier or balun. 
  • A balun is a balanced input to unbalanced output device.


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microphone-transformer-balun.png


  • Figure shows microphone transformer that plugs directly into high impedance amplifier input. 
  • The XLR socket at the other side allows low impedance microphone to connected via a long lead. 
  • A metal screening case in the transformer acts as a balun and impedance matching device.

 

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