Condenser Mic for Under $20

In this Instructable I will show you how to make a simple condenser microphone for under $20. I used a tea tin for my microphone's case, but you can use whatever works for you.

List of Parts:
Condenser mic cartridge (I got mine from the component bins at Radio Shack)
10.0UF/100VDC metal-poly capacitor
1000PF 100V ceramic disc-style capacitor
9V battery snaps
2.21K ohm 1/4W 1% metal film resistor
Male XLR plug
9V battery holder
Casing for the mic (I used a Zhena’s Gypsy Tea tin)
Wires
Heatshrink tubing (optional, but can help prevent shorts)

All parts can be found on DigiKey.
Originally posted this (along with the schematic) on my blog. You can contact me there if you have questions.

Solder the disc capacitor between the mic cartridge leads. Be careful doing this as excessive heat can damage the cartridge.

Solder together pin 1 and the ground pin on the XLR plug. Solder the 10.0UF capacitor to pin 2 and, to pin 3, a wire long enough to reach from the XLR plug to the mic cartridge when you put the whole assembly in its case. Add heatshrink tubing as you go, if you’ve opted to use it.

Solder the positive lead (in this photo, the red wire) from the 9V battery snaps to the wire coming from XLR pin 3. Solder the negative lead to the wire coming from XLR pin 2. Solder wires onto the mic cartridge if you find you need more distance between the XLR plug and the cartridge, and then solder the negative lead from the cartridge (the one with extra solder/connections running from it) to the wire coming from XLR pin 2. Solder the other lead to the wire coming from XLR pin 3.

You could use the microphone now, if you like. In fact, you probably should, just to make sure that you soldered everything together right before you go putting it in a case. Everything from here on out is up to you and depends entirely on the sort of case you decide to use. Since I used a tea tin, I'll proceed assuming you did the same. Consider this step and the remaining steps optional.

Carve out a few holes in your tea tin. You’ll need three on the bottom (one for the XLR plug to fit through, two for the screws to hold it in), several on the top to allow sound in, and two on the side for the screws for the battery holder. I used a box cutter and a twisting, drilling motion for this, though I would recommend a dremel or something of the sort if you have access to one. As you can see in this photo, I slipped a bit with the box-cutter while cutting out the XLR hole, which led to a bit of trouble in actual use with the action of connecting and disconnecting the mic breaking the thin bit of metal left around one of the screws.

Pull the whole assembly through the XLR hole and fasten it to the case. I used screws scavenged from old video cards, as these came with nuts and were small enough to fit through both the XLR holes and the battery holder holes. I also used a bit of electrical tape to hold the microphone cartridge up against the lid of the tea tin.

And there you have it!

Based on the project at www.christianmusicweb.com/microphones/mic_project.html
Original instructions posted at http://cyanyears.wordpress.com/2010/12/22/how-to-make-a-condenser-mic-for-under-20/