low voltage microphone preamplifier circuit schematic

Low Voltage Microphone Preamplifier Circuit

This is a low voltage microphone preamplifier circuit with a 1.5V power supply. The reference, with a 500 kHz unity-gain bandwidth, is used as a preamplifier with a gain of 100. Its output is fed through a gain-control potentiometer to the op amp, which is connected for a gain of 10. The combination gives a 60 dB gain with a 10 kHz bandwidth, unloaded, and 5 kHz loaded at 500 Ω . Input impedance is 10 kΩ.

Potentially, using the reference as a preamplifier in this fashion can cause excess noise. However, because the reference voltage is low, the nose contribution, which adds root-mean-square, is likewise low. The input noise voltage in this connection is 440-500 nV Hz, about equal to that of the amp.

Microphone preamplifier circuit diagram

low voltage microphone preamplifier circuit schematic

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  • BungledB

    So it turns out that this doesn’t actually work as drawn. In operation, because pin 3 is too high a voltage, the output is pushed to positive saturation.

    But if you go back to the data sheet for the LM10CN which is where this circuit comes from, and change R2 to 1M as shown there, it does work as described.

    It’s quite noisy in use, though – even although the supply voltage is low – so use it with caution.