Microphone Issues ...

[Mr CCE]

Hi all,

I'm having trouble testing small electric microphones. I'm testing the mic directly by a digital voltmeter (mV range) and I'm getting absolutely nothing. Also, I tried a non-inverting amplifier of gain 100 and the result is < 0V.

What gives??

 

[ericgibbs]

Hi all,

I'm having trouble testing small electric microphones. I'm testing the mic directly by a digital voltmeter (mV range) and I'm getting absolutely nothing. Also, I tried a non-inverting amplifier of gain 100 and the result is < 0V.

What gives??

hi,
Post your OPA 741 circuit.

 

[Nigel Goodwin]

You can't test using a multimeter, get a scope.

 

[audioguru]

There is no such thing as "an electric" microphone. If it is an electret mic then it must be powered in order for it to work.
Look in Google Images for Electret Microphone to see if your mic looks the same. Then look in Google for Electret Microphone Preamp Circuit.

 

[Hero999]

There is a way to do this with a DVM.

Connect a sub-woofer to the secondary of a 9VA 6V transformer, put the microphone next to the sub and measure the output of your op-amp with the DVM.

DVMs are designed to only work at mains frequencies and they need a continuous signal to work well. The sub-woofer connected to the mains transformer will produce a loud mains frequency hum which should be picked up by the microphone and amplified to a level the DVM should be able to detect. Make sure the transformer is powerful enough to power the speaker and that the speaker can handle the power 6V into a 4R speaker is 9W which fine for a sub, just make sure the transformer is up to the job.