simple microphone preamplifier

Posted on Feb 4, 2014

The circuitis a simple one transistor amplifier with amplification of about 30-40 dB (depends on transitor, temperature and voltage). The dynamic mic input is just a simple one transistor amplifier circuit with nothing special in it. LED D1 is inthe circuitto show thatthe circuitoperates. The voltage drop caused by LED (around 1. 8V for RED led) ha

simple microphone preamplifier
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s been taten in account when designing theamplifier circuitbuilt around Q1. Resistor R4 and capacitor C5 make a filter to filter out possible noise from battery or other power source which is used tofeedthis circuit. Capacitors C1, C2 and C3 are used to block the DC bias on Q1 base to flow out of microphone input to microphone (the polarity of all capactors is straigh line = + and curved line = -). Electret microphone input has a resistor R1 fo feeding current through electret microphone capsule when it is connected to the electret microphone input. Electret microphone needs some current (about 1 mA) flowing through it to operate, because there is asmall amplifier circuitinside the microphone capsule. This circuit is suitable for all typical cheap electret capsules which available from any electronic component shop. Because electret microphones have higher signal level output, it is quite easy to overdrive the amplifier when you shout to electret microphone. The circuitis bet to build to a small metal box like in the picture above. Put the 9V battery inside the case too. Battery power and metal box keep external noise and interference sources away. I used standard 6. 3 mm jack for dynamic microphone and 3. 5 mm mono jack for electret micrphone both installed to from, panel of the metal box. The LED and power switches are also installed tofront panel.

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