JAY X said:
Attached is a simple schematic of a volume pot in its own pcb board, wired in between two stages on the main pcb: the signal comes from the output of the preceding stage, enters the pot and goes to the fader amplifier. To avoid gnd loops in the main pcb, i wired the gnd differentially.... i think it is correct... but i'm not completely sure... ???
That is not differential. I think you want to learn more about grounding between multiple circuits which is a different topic.
You don't need differential connections between boards in the same piece of gear. One could argue you don't need differential connections between two pieces of gear on the same rack. The extra circuitry would add more noise than it fixes.
Differential connections use two signal conductors where one of the conductors carries the same exact signal as the other but inverted. The receiver then takes the difference between the two signals and in doing so any in-phase noise will cancel out.
Also, unlike a regular "single ended" connection where one signal conductor is used referenced to a ground, the differential connection (also called balanced) is not referenced to ground and therefore it cannot carry ground currents and thus it is immune to ground noise (ground loops).
But circuits in the same piece of gear are not (should not) have long runs of cables that would be picking up noise. And ground wires should run to each board from a single point on the power supply out to each circuit in a branching or star fashion such that there are no loops that could carry ground currents between boards (again no ground loops). Also, any signal wires that are high impedance, should be shielded but the shield wire should only be connected at one end.
So you probably want to just learn about grounding multiple circuits together. Incorrect grounding is almost always the most likely cause of excessive noise in a circuit. If something is buzzing, you have a grounding problem.
You might choose to make inputs and outputs differential to eliminate ground currents between other peices of gear or if the gear is going to be connected to long cables in an environment where there are other noise sources (like a radio station). But again, these are really two different topics.