microphonepreampsoundsound card
Can I assume that the signal from an electret microphone capsule is inverted due to common source configuration of jfet?
I would like to have non-inverted signal on my sound's card line input. Then I pick up inverting preamplifier project.
What about microphone input. Does it have inverting op-amp?
If you just want a simple flat gain including DC around ground, then about the only meaningful difference is that the non-inverting configuration has high input impedance and the inverting a controlled input impedance referenced to ground.
The differences matter more when you want to do other things, like bring the DC gain down to 1, not load a mid-supply reference, keep turnon fast, etc.
It gives you:
As shown, you get DC feedback via R1+R2. But R1/C1 forms a low pass filter for signals coming from the collector and going to the base. Less negative feedback means less reduction in gain for high frerquencies. Cancel out all those double-negatives and you're left with a high-pass filter.
The transistor below corresponds to Q5 in your drawing.
simulate this circuit – Schematic created using CircuitLab
Best Answer
As others have stated, in general, in many situations not only does not matter as absolute phase is impossible to guarantee with audio over more than a short distance.
However, if you you wish to combine the output with other microphones then it is necessary to ensure that they all have the same polarity signal with a pressure wavefront.
This would be used for example in beam-forming or to locate a source of sound. Most cell-phones use multiple microphones to aid in noise cancellation to reject background noise.
Especially at low frequencies multiple microphones can be coherent over several feet.
Although the FET amplifying stage does invert the signal it also depends upon how the elecctret microphone capsule is designed and connected. If the capsule gives out a negative going signal for a positive pressure change the output from the combination will be positive going.
The information you need might be in the datasheet.