ADAU1761 IMPEDANCE MATCHING AND GAIN

Hello Vinaybhatt,

This is a large design nut just simply a few parts to use in front or after the codec/DSP. A 150ohm mic input preamplifier will be a significant design and the easiest would probably be to use a transformer. What kind of microphone are you using?

Then 20Vrms into 600 ohms is significant level!! +28dBu and into 600 ohms means it will be dissipating almost 3/4W! This is approaching a power amplifier so it would have to be more than just a standard OpAmp on the output. 

So this means you need a speaker amplifier. Here is our selection guide for Class-D amplifiers.

Selection Table for Class-D Audio Amplifiers | Parametric Search | Analog Devices

You might have some solutions for the preamp by looking at the selection guide for preamps.

Selection Table for Microphone Pre-Amp Audio Interfaces | Parametric Search | Analog Devices

There are just so many different options that I cannot just give you an answer based on one sentence. 

Dave T