Electret Microphone Last changed 2018/08/03 10:51 New name B I U S link image code HTML list Upload - + How to use a electret microphone with a balanced phantom powered input. We use the Primo EM172, a 12€ high quality electret microphone. The circuit presented here can be use to build a monophonic streambox, or with two of them a binaural head. The presented circuit power the electret microphone with a bias voltage determined by the value of a zener diode. Usualy 5 volts is enought, but I find out 12v works better with the Primo EM172. It use the +48v from the phantom power, and output a balanced signal. This way, an extended length of cable can be used with very little background noise. You will need: Resistors: 2K2 1/4W 1% x2 22K 1/4W 1% x2 Capacitors: 10nf 100v mylar or ceramic x1 10uf aluminum electrolytic x3 All capacitor must rated for a voltage above the zener voltage used, for exemple vith a 12v zener diode, 18v rated capacitors ar fine. Beware of the polarity of the capacitors, each must be wired as shown on the schematic. Diode: zener 12v x1 Other: XLR male connector Microphone cable, shielded stereo Electret microphone (primo EM172). The circuit is quite simple [http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/primoBalancedSchematic.jpg|left] Here is where the parts goes. [http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/primoBalancedImplant.jpg|left] The circuit can be assembled on test board. Butif you want to print it, you can find the eagle files [here|http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/PrimoPreamp.zip]. Here are a few complete circuits. [http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/DSC_0989.JPG|left] It has been working outside for years, and is proven to be reliable. However, if left outside, coating the circuit is a good precaution, otherwise the humidity from the air with the +48v will disolve your trace, as it happend to me: [http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/IMG_1275.jpg|left] That is what happend with uncoated circuit outside. Some sort of wind protection is recommended. [http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/IMG_1278.jpg|left] [http://gregoirelauvin.net/ftporth/locus/locusWiki/locus%20wiki/primo/IMG_0969.jpg|left] You can listen to this very circuit [here|http://locus.creacast.com:9001/aix_provence_st_jerome.ogg]. Summary of changes Password Syntax