Electret microphone element driver, & preamp, with varying impedance output...

[Satchmoeddie]

I want to put an electrect element in an old Astatic high impedance case, but I will require variable impedance outputs. I will need low (<600 Ohms), so an op amp preamp would be fine, but I also need medium, 1K-10K, and high impedance for old vac tube transmitters.. Is there an easy way to make a preamp or a buffer circuit after a preamp, and EQ that I can switch the impedance on? I do have some Sure Brother's 11K elements, but I'd rather use a 50 cent Hosiden element. Eventually, I can spin form a new diaphragm, and retack the X-tal element to the new diaphragm, using a small spot welder, but that is an expensive repair, and want some other options, that will allow a preamp or EQ even if it is unity gain or even an attenuated level out. I just need to have some way to select the output impedance, and switch it easily. Looking for some ideas here. I have various gear that spans 100 years, and takes various types of input Z for the mic input. Thanks!

 

[FvM]

Re: Electret microphone element driver, & preamp, with varying impedance output...

I hear a basic misunderstanding about microphone operation. There's absolutely no need for impedance matching, Rsource <= Rload should be sufficient. In practice a simple electret microphone circuit with 1 or 2k resistive output impedance can be expected too fit all applications, using an additional voltage divider if the output level is to high and the transmitter has no level adjusting means.

A 300 Hz (or similar) "speech" high pass filter can be helpful.