Electret mic (3 wire capsule)

[birt]

I have built an electret mic as found on Moosapotamus' website. (www.moosapotamus.net) i used a 2 terminal capsule and modified it so the internal FET is a source follower instead of common source. it's done by cutting the trace from the source to the case (ground) and reconnecting the case to the drain. the signal now comes from the source instead of the drain.

but i want to build some more and i have a big pile of 3 terminal electret capsules. they have presoldered leads. one is a normal wire and one is shielded, the shield is the third terminal and the case. since the shield is connected to the case i just have to find out what wire is the drain and what wire is the source. and i don't know how to do that.

i can guess... if the 2 terminal version normally takes the signal from the drain and has the source connected to ground, i would guess that it is done the same way on the capsules i have. so the shielded wire would be the drain and the other one would be the source. modding it would then be easy. i just connect the shield to the drain and take the signal from the source.

but how do i know if my guess is correct?

[popstudioguitar]

I would suggest you have a look at a group called micbuilders (yahoo)...tons of info, schematic and pix.

A great source of knowledge on modding electret capsule.

Cheers,

Christian
www.pepcotubeamp.co.cc

[birt]

i could do that but i'm kinda hoping i could find my answer here or elesewhere so i don't have to make a yahoo account. i have enough e-mail adresses and other accounts to check.

[birt]

here's a picture. the 2 terminal version and 3 terminal versions. both 3 terminal electrets have one wire shielded by the base connection.

[tranceracer]

I needed a mic at the end of a long cable so I built this stereo mic using the Linkwitz mod ckt.  I works quite well and it's on a mini breadboard using a 16 pin socket so I can change resister and cap values.  The only thing is that the cable I used, tho it's 100 sheilded, is very stiff and xfers a lot of handling noise to the mic elements.  This is relatively minor because once the mics are in place there is generally minimal movement.  This only becomes an issue if the mic needs to be re-positioned in the middle of a recording. 

This is a prototype so the next version will use more flexible cable and isolate the mics better.

Anyway here are some schematics and pics:








If you're interested in more DIY mic ckts PM me and I'll send you a PDF of some more.