Introduction: Electret Microphone Preamplifier

About: I am electronics and robotics enthusiast and love making new and innovative things everyday!

Hello Everybody! I'm back with another with another instructable. This one is about how to make a Electret Microphone pre-amplifier. With this, we can covert sound energy to electric energy and amplify it a bit with the help of the preamplifer. It works incredibly well and can be easily built with some electronic components. so, let's get started.

Step 1: Gathering the Parts

Tools required

Solder Iron

Solder wire

Glue Gun (optional but handy)

Wire stripper

Parts required for making the preamplifier with the electret mic are:

NPN Transistor-(I used BC547, any similar one would work)

Capacitor - 4.7uF X2

Electret microphone


SPST Switch (I couldn't find it , so I used a SPDT one)


LED (I used red)

9v Battery

9v Battery Connector

Electronics Enclosure (I used a cardboard box and decorated it)

Audio Jack - 3.5mm (for music players, etc.)

- 1/4 inch (for amplifiers)

Resistor - 1K (for LED)

- 2K2



Step 2: Getting the Concept - the Theory

An electret microphone is a type of electrostatic capacitor-based microphone, which eliminates the need for a polarizing power supply by using a permanently charged material.

An electret is a stable dielectric material with a permanently embedded static electric charge (which, due to the high resistance and chemical stability of the material, will not decay for hundreds of years). The name comes from electrostatic and magnet; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. Electrets are commonly made by first melting a suitable dielectric material such as a plastic or wax that contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field. The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a permanent electrostatic "bias". Modern electret microphones use PTFE plastic, either in film or solute form, to form the electret.

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

Transistor as an amplifier

The common-emitter amplifier is designed so that a small change in voltage (Vin) changes the small current through the base of the transistor; the transistor's current amplification combined with the properties of the circuit mean that small swings in Vin produce large changes in Vout.
Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both. From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. The first discrete-transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved. Modern transistor audio amplifiers of up to a few hundred watts are common and relatively inexpensive.


Step 3: the Schecmatic

Follow the schematic and build the circuit. I recommend you to first prototype the circuit on a breadboard.

Step 4: Building the Circuit

Now you can build the circuit on a perfboard. Be a bit careful because this has a number of of board components like the mic, switch, battery connector, LED,etc. Solder them carefully and then run a hobby knife or hacksaw blade between all solder joints to prevent any unwanted pieces of solder from hanging around there. Use heatshrink tubing or insulating all wires. I also used it to group them for ease.

Step 5: Testing the Preamplifier

After building the circuit plug in the battery , turn on the switch, connect the audio cable to a set of speakers, music player or an amplifier and then finally speak something on the mic. You should be able to hear your sound absolutely clear from the speakers. If however your sound is not clear, melt and again solder all dry solder joints and especially check the resistors and capacitors. If it is not working then check all the connections and wires and correct them.

Step 6: Assembling and Enclosing the Circuit

You may enclose the circuit in an electronics enclosure. I enclosed it in a cardboard box. Be careful not to break any wire. Put the audio jacks, switch , mic and LED so that they can be seen / accessed from outside the box.

Step 7: Decorating Your Preamplifer (optional)

Now that you have successfully made the preamplier, you can decorate it to look more pleasing.

I covered it using some sort of handmade paper and put blue insulating tape on the edge as the border. I added some labels on the sides.

You can enjoy using the microphone and can record your speech or songs while plugging it into the computer , amplifier, etc.Please comment below if you have any doubt or suggestions.

Have a nice day! Thanks!

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