Siegfried Linkwitz describes a way to modify an electret so that the internal FET is used as a source follower http://www.linkwitzlab.com/sys_test.htm#Mic.
He uses a 10 k source resistor as a load. I wonder if the distortion and EMI performance can be further improved by using a current source instead and placing the non-inverting op-amp input directly at the node rather than at the end of a cable.
- Any idea what a good current is, i.e. what typical threshold voltages for the internal FETs are?
- What kind of current source is best? Conventional bipolar with cascode?
- Using a FET op-amps won't hurt because the impedance is really determined by the dynamic output impedance of the FET.
He uses a 10 k source resistor as a load. I wonder if the distortion and EMI performance can be further improved by using a current source instead and placing the non-inverting op-amp input directly at the node rather than at the end of a cable.
- Any idea what a good current is, i.e. what typical threshold voltages for the internal FETs are?
- What kind of current source is best? Conventional bipolar with cascode?
- Using a FET op-amps won't hurt because the impedance is really determined by the dynamic output impedance of the FET.
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