Hello everyone. I spend some time reading posts on this forum and saw how helpful it was for some people, so I want to ask for someones help in my project.

Please forgive me a lot of mistackes and may be misunderstandings in my texts - English is not my native language...

So, my idea is to make a simple sound mixer that will mix sounds from some built-in player (for example - mini MP3 DFPlayer) and from dynamic microphone. The volume of mixing should be controlled by a microcontroller like Teensy or Arduino.

Here is simple diagram of how I'm viewing this system:

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To understand how to realize the schematics of analog mixing I found this stuff:

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And took from here one line with op-amp for microphone and one Line-In line to bring the sound from DFPlayer to the op-amp in the end, where the microphone and Line-in lines are meeting. All this should be done 3 times, to provide 3 different tracks but with the same microphone input, like shown on the diagram above.

But when I started to make tests (first with one track line and one microphone), I got some noises on the output... What's strange, that if I'm starting to play track on DFPlayer and make thats volume down by the analog potentiometer, there is still a lot of noise on the output. But if the microphone line (I mean final resistor which connect microphone line to the last op-amp) is unplugged from whole circuit, the noise is gone... And the otherwise - when I use only microphone line with the player line unplugged, everything sounds good and without noises...

After a lot of tests and tries to improve the circuit I found the Teensy Audio Adaptor, which (I thought...) could solve all my problems with analog sound mixing, no matter, that it's not the cheapest solution for so simple (or not?) system...

So now the plan is to take sound from DFPlayer and microphone to the Audio Adaptor Inputs channels and mix all stuff there.

But here is some questions...

1. If a dynamic microphone can be directly connected to the Audio Adaptor MIC input or should I first take it through the op-amp and the connect to regular Line-in of the Adaptor?

2. If the Adaptor can be controlled by the Teensy (or another controller) but in the Master mode - because I only need to control the volume of channel mixing and nothing at all. But I also want to use several Adaptors at the same time to provide several tracks playing and mixing with microphone, how I said previous. (The idea was like to connect all adaptors to the same I2C line, because all of them should get the same commands to control the mixing volume equally)

I'm sorry for so much text and it's may be not clear what I'm trying to explain, but I'll be very glad for some help!

If somebody have any idea of simple schematics for analog version of this project it will be very helpful because it's, I hope will make the project cheaper...

But if the Teensy Audio Adaptor version is more reliable, and it's possible how I want to use it, also grate news!

So how they say... "Help me Obi Wan Kenobi, you're my only hope..."