Here’s a simple audio mixer circuit that you can use to connect up to 4 mics on your amplifier. The potentiometers or volume controls are not part of the PCB to make it smaller.
About the Circuit
The circuit is made of 5 preamps, 1 for each channel and 1 for the main. It only use 1 NPN BJT per channel. I will be creating a separate post regarding the preamp so that this post will not be long. 🙂
I am too busy for now to build my own design but this simulation program is very useful to verify that my design is really working. You can download the simulation file on the download page. You can play with the values and see the response of the circuit. The simulation program can be downloaded for free. The download link of the simulation software can be found on the download page. In case you do not know yet – I am using Simetrix software. 🙂
The PCB design is made using Eagle PCB. It is small and single layer so that it will be easy for DIY. You can download the design files at the bottom of this page.