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An ECM microphone preamplifier circuit

2015-01-04 09:22  
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This article describes an ECM microphone preamplifier circuit. Schematics can combine text look better grasp of this principle. Two transistors should be low noise types. In the original circuit, I used to be a BC650C ultra low noise devices. These transistors are now hard to find but  BC549C  or BC109C are a good alternative. This circuitry is a self-bias and to its quiescent operating point at about half the supply voltage at the emitter end of the transistor. The electret condenser microphone (ECM) contains a very sensitive microphone element and an internal FET preamplifier power supply in the range of 2 to 10 volts DC, is therefore necessary. The right of the ECM is also available from Maplin Electronics. 1 k resistor limits the current microphone. 2 k2 This resistor should be increased if the supply voltage exceeds 12 V DC is not used if the microphone into a dynamic. Output impedance is very low, suitable for driving cable distance of 50 meters. Therefore, the shielded cable is not necessary.



ECM preamp

The frequency response measured across a 10k load resistor is plotted below simulated using a 12V power source:

bode plt

The noise response of the amplifier measured across the 10k load is shown below. Please note that this plot was made with the mic insert replaced by a signal generator.

noise plot


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