Source follower electret mike -> use with current source?

capslock · 28th February 2003, 11:24 AM

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.

Morph · 28th February 2003, 12:54 PM

There is also info onrods site regarding converting an electret mic to dramatically improve its performance.

28th February 2003, 11:24 AM	#1
capslock diyAudio Member Join Date: Feb 2002 Location: Germany	Source follower electret mike -> use with current source? 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.

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28th February 2003, 12:54 PM	#2
Morph diyAudio Member Join Date: Feb 2003 Location: London	There is also info onrods site regarding converting an electret mic to dramatically improve its performance.