Grounding - multiple units (guitar) - head hurts

[HankMcSpank]

What's the ethos with respect to grounding with interconnecting multiple units wrt Guitars?

I have a setup as follows....

Unit 1 - a Guitar -> midi converter, which has the following connectivity

A USB connection (if you look at the USB cable spec - it has a ground, presumably derived from the mains at the PC end?),

A guitar input (has a ground)

A guitar output (has a ground)

This unit's power is derived from two core AC (therefore I'm assuming no 'true' ground - for the want of a better expression)


Unit 2 - a firewire type soundcard, which has the following connectivity....

A firewire connection back to the PC (with ground)

A guitar input socket (with ground)

This unit's power is derived from a wall wart.


So my question - wrt grounding how do these all hang together?

Is there a doctrine where say one device should provide a good clean ground, or can they all have their own signal grounds - if the latter what happens when they're all tied together?


I'm trying to wrap my head around how I should wire the inside of my guitar (which in itself has active circuitry that can be powered by 2 x 9V batteries or power sourced from unit 1!)

[Dan2]

"This unit's power is derived from two core AC (therefore I'm assuming no 'true' ground - for the want of a better expression)"

you are mistaking ground for your earth leakage wire. the negative pin of the rectifier is the ground.

the ac voltage goes through a transformer, which isolates the voltage. this then goes through a rectifier which gives you dc voltage.

in other words, if your transformer pushes out 20v dc, your voltage on the positive pin of the rectifier will be 20 v more than on the negative pin, regardless of what the voltage is on the negative pin wrt other power sources.
JUST BEAR IN MIND THIS IS ONLY FOR TRANSFORMERS! i believe the computer power supply is not isolated from mains. i am pretty sure connecting the grounds of 2 separate computers is dangerous.



so for your example, all ground wires should be connected together at some point - this creates a reference point (0v) for all the devices.