True bypass: how to deal with GND?

Question

I'm building custom hardware for my studio and one question keeps popping up: how to treat the GND connections?

A simple example: I have two mono inputs which go into a switch and from there to either stereo output A or stereo output B. One way to wire this would be to connect all GNDs directly (i.e. wire all GNDs of the input and output jacks together without a switch in between), the other way would be to use a switch with more poles and switch GND and V+ rather than just V+. Obviously with more complex setups there are a lot more connections required to route all GNDs, i.e. a lot cables to solder. Are there benefits to this approach or am I just wasting my time?

Answer 1

There are two possibilities:

• Use unbalanced connections, like in guitar pedals. In this case, you must have exactly one contiguous chain of ground connections (regardless of whether a device is bypassed, it must be shielded to avoid picking up capacitive interference, and any loop in the connections will pick up inductive interference). Bifurcated routings are a nightmare in this case, which is why unbalanced connections are largely abandoned in studio applications.
• Use balanced connections. This is strongly preferrable: in this case it doesn't really matter what the ground does because any interference cancels between the signal wires. Each device can then just use the ground from its power socket, which is anyway a good idea for safety reasons. In practice, it can still makes a slight difference whether you have ground connected also via the line or not (because no device has perfect common-mode rejection); usually it doesn't make sense to connect ground but sometimes it can, certainly if a device has no ground of its own.

In neither case does it make sense to disconnect the ground on bypass. With balanced connections it can make sense to have a switch that only controls ground, though.