Electret microphone amplifier with analog MEMS microphone

Question

I'm currently using an INMP401 MEMS microphone breakout board (https://www.sparkfun.com/products/9868) for the purpose of having a microcontroller read and sample the output. Now I also want to listen to sound picked up by the microphone through headphones, so I need to use a different amplifier. This MAX9814 amplifier looks good with automatic gain control, however it is described as being for electret microphones: https://datasheets.maximintegrated.com/en/ds/MAX9814.pdf

I connected the output of the MEMS breakout board to the input of the MAX9814 amplifier. There was a lot of noise. Could the MEMS microphone output be directly connected to the input of the MAX9814 (surpassing the MEMS breakout board op amp amplifier)? Is there a problem with using an analog MEMS microphone with this IC? I'm not sure why it specifically mentions electret microphones. I'm open to better suggestions too...

Answer 1

No. That breakout has an op amp on it but that max9814 has an input with a bias voltage on it for powering the mic. So you don't want to connect the output of an op amp (which looks like it is biased to 1/2 VCC btw) to some current source. The two will just fight each other. And besides, you don't want to amplify things twice.

So either just connect a regular electret to the max9814 or just connect the mic breakout to your uc. In the later case it's already biased to 1/2 VCC as well. In the former case, note that a regular electret mic is actually a very good mic. Not sure that the mems mic is really that much better. Also, note that it is highly unlikely that your microcontroller is going to be fast enough to do anything serious with audio.