I am using a VS1053 (on a SparkFun Music Maker shield) to provide audio for my project. I am taking a line out signal and inputting it into an op amp for signal processing, ultimately being input to an Arduino.
The op amp(s) are using Vcc and ground from the Arduino as their power supply. The module with the VS1053 also uses the same supply connections.
But line out is referenced to the audio ground created by the VS1053. In order to see the input signal, somehow the op amp and VS1053 must have a common reference.
An early circuit connected the audio signal ground to the circuit ground. But this is explicitly prohibited in the VS1053 data sheet. It seems to work but probably does do as a matter of luck. And will likely fail eventually.
How do I connect the line output of the VS1053 to an op amp?