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The OP27 Fixed Gain Transformerless Microphone Preamplifier

2015-01-02 23:48  
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You can see a simple but effective fixed gain transformerless microphonepreamplifier circuit diagramin the picure below. The circuit amplifies differential signals from low impedance microphones by 50 dB and has an input impedance of 2 kOhms.

Fixed Gain Transformerless Microphone Preamplifier Circuit Diagram

The OP27/37 operational amplifierhelps to preserve bandwith because of the high working gain of the circuit. If you need the microphone is to be unplugged, a dummy resistor Rp may be necessary (source: analog.com)