I'm implementing the following audio single-ended to differential converter for an ADC:
This is the reference design for the PCM1804 that I intend to use.
What would happen if I do this:
Would it still work?
The reason I'm interested in doing this is demonstrated in the following diagram:
simulate this circuit – Schematic created using CircuitLab
Even though I'm using an isolated power supply for my DSP, my amplifier internally connects the signal ground to the chassis. There's clearly a huge ground loop, consisting of the ground shield in the RCA cables and the car chassis that is a big source of noise.
I thought inserting a capacitor in the way of the ground as shown above would break this ground loop. But apparently, this is not a good idea. Any other suggestions are much appreciated.
I am aware of ground loop isolator transformers, but that's a band-aid fix, and they create a large amount of distortion.
Best Answer
The whole circuit you provided is a single ended AC coupled to the differential output.
1st stage buffers (x -1) then the output is AC coupled on its output and AC coupled input for the noninverted on the bottom.
The output is a differential analog signal. But the input impedance is unbalanced and does not convert stray noise current or ground shift to a differential noise voltage such that the Common Mode noise cancels out.
Maybe what you want for better immunity is a differential amplifier with precision matched resistor ratios or an Instrument Amp (INA).
Your suggestions won't work at all as others have explained.
The cct that works has an input impedance of 4.7k//{3.3k+Z(10uF)}
There are other ways to do this but that was not your question.