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OPA313: OPA313, OPA344

Part Number: OPA313

Dear TI-san,


I decided to use a microphone"A" with an output impedance of 5.2kΩ and set resistance of the amplifier input to 3.6kΩ.

3.6kΩ is intended to minimize power supply noise of connected laptop computer.


After that, I changed from microphone"" to icrophone"B", so I was allowed to discuss change of op amp peripheral circuit with E2E.

And I understand that 3.6kΩ of microphone amplifier input resistance was obtained with consent TI-san.


The manufacturer of microphone"B" insists on changing input resistance of microphone amplifier from 3.6kΩ to 36kΩ, which is 10 times larger.

The rationale is that output impedance of microphone"B" is 5.5kΩ.


Please let us know your opinion.





  • I would like to confirm with you that circuit and resistance values listed are okay.

  • Hi Shinya,

    microphones are usually connected to the amplifier by performing "voltage matching" (don't know whether this is the right term in Englisch Relaxed) where the load resistance is at least five times (better ten times) the source resistance of microphone. So the manufacturer may be right.


  • Hello Suzuki-san

    The output impedance of the microphone represents the electric characteristics of the output signal. The insistence of 36k means they think the microphone works better when lightly loaded. Where it outputs voltage(s) at very little AC current. 

    Perhaps they dislike that the bottom output drives a 'virtual zero' (op amp IN- pin) [180 + 3.6k] while the top output drives towards ground [180 + 3.6k + 13k||10k||2.2nF].  Would mic B support be happier if the load on both mic outputs were the same? Three op amp solution.

  • Dear Kai-san, Michallick-san


    Thank you reply.


    I would like to use your advice to determine part constants.