A simple, high-quality DIY microphone pre-amplifier with switched gain. The background for this project was that I needed a simple but good microphone preamp for doing acoustic measurements. I needed a switched gain to be able to reproduce the gain setting in a more predictable way than what is possible with a potmeter. I could not find any existing DIY designs, so I decided to make one.

The design is based on the excellent THAT1510 or THAT1512 preamp ICs. It is also compatible with SSM2019 or INA217. I have followed all THAT’s datasheets and app-notes to implement a robust, best-practice design.

A goal was to use simple through-hole parts that I and other DIYers usually have in our parts drawer. So there are no additional IC’s or voltage regulators for example, it just uses simple transistors, capacitors and zener diodes for supply filtering and regulation. I selected affordable switches and connectors to keep cost down. Many parts can be substituted without sacrificing performance.

There are two versions of this design, one suited for a desktop encolsure with gain switch on top, and one suited for a rack-mount enclosure with gain switch on the front.

github.com/ojg/thatmicpre