Phantom Powered Microphone Preamplifier – Low Noise – Professional Quality

The project presented here is a professional quality Phantom powered Microphone pre-amplifier. The project is built using the INA163 chip from TI. The Chip is a very low-noise, low-distortion, monolithic instrumentation amplifier. R2 and R3 provide a current path for a conventional 48V phantom power source for a remotely located microphone. A slide switch SW1 allows phantom power to be disabled. C6 and C8 block the phantom power voltage from the INA163 input circuitry. Additional input protection against ESD and hot-plugging, four 1N4148 diodes D1, D2, D3, D4 connected from the input to supply lines. R7 and R8 provide a path for the input bias current of the INA163. Gain is set with a variable resistor, PR1, in series with R4. R4 determines the maximum gain. The total resistance, R4 + PR1, determines the lowest gain. A special reverse-log taper potentiometer for PR1 can be used to create a linear change (in dB) with rotation. LED D5 is used as a power indicator. L1, L2, C7, C10, and C11 components protect the inputs from EMI and RFI noise.