sensitivity of microphone....

[keith1200rs]

You can certainly get microphones down to 1Hz:

**broken link removed**

One possibility with a cheaper microphone is to boost low frequencies if you know where the LF corner frequency is. You would have to check, but if it was 6dB/octave then you could effectively end up with a flat response. You would obviously also boost LF noise, but it is one solution.

Keith.

 

[Audioguru]

The very expensive microphone that goes down to 0.5hz is a condenser type that needs an external 48VDC power supply.

 

[Kinshoro]

I am trying to implement a differential amplifier using the signals from both my microphones...... Currently I am using AD627 as my differential amplifier... Can anyone recommend me a better differential amplifier for my application(low noise, low power).

 

[Audioguru]

I am trying to implement a differential amplifier using the signals from both my microphones...... Currently I am using AD627 as my differential amplifier... Can anyone recommend me a better differential amplifier for my application(low noise, low power).

Your differential amplifier did not work because its inputs had no DC bias voltage and it had no negative feedback.

 

[keith1200rs]

The AD627 is an instrumentation amplifier. That isn't what you need for microphone amplification. What is your target current consumption and power supply (single 3.3V, 5V etc)? What GBW? What minimum frequency?

The lower the noise you want the more current it will take. Most manufacturers web sites have selection guides where you can specify maximum current, GBW and noise.

For example, LT6234 is low noise at 1.9nV/rt(Hz) and takes around 1mA; LMV651takes 116uA but has 17nV/rt(Hz) noise.

If you are looking down to 1Hz-130Hz I think you mentioned before, you really need to be looking at the 1/f noise rather than the midband noise.

Keith.

 

[Kinshoro]

https://www.jimfranklin.info/microchipdatasheets/00695a.pdf

At this link page 4, figure 4..... I found a way to amplify, filter and differentiate my microphone signals..... The question I have is would this work with my microphone signals which have a variable DC offset. Would the circuit act as an oscillator if the dc offset of both the microphones were a little different from each other???? They show a reference voltage across the negative input of of the first opamp.... then would there be any problem in DC offset mismatch of the input signal and the reference voltage???? I have attached the image of the circuit in case you have trouble finding it...

 

[Kinshoro]

Is this circuit similar to the internal circuit of the AD627 instrumentational amplifier or are they completely different... Which one would work better for my purpose??

 

[keith1200rs]

It's drawn a strange way, but looks like the two opamp instrumentation amplifier configuration, instead of the three opamp version. According to Horowitz & Hill, it needs precise resistor matching for good CMRR, but it is not a configuration I ever remember using.

Keith.