Grounding cable gauge size

The Andrews should have a filter network in it like the Groundmaster to make sure what goes in does not came back through.

I just tried connecting a ground wire from an outlet to my grounding box and I heard hum.

ozzy

Similar to my incident. Must be making a ground loop. Don't forget, many chassis grounds can be signal grounds on some devices. My amp's ground to the wall is also the chassis and XLR grounds.

Here is a simple device I made with a spare Furutech clamshell plug and banana jack. Takes the banana plug straight to ground only (one wire inside). With the clamshell you can grab the banana nut and hold it tight to the plastic shell when you close it up.

bugredmachine

The Andrews should have a filter network in it like the Groundmaster to make sure what goes in does not came back through.

What makes you think it's just an empty box with a simple wire in it?

It would never be an empty box. It would have to have filters for certain frequencies and perhaps some diodes to let the noise escape and not return.

I never said the Andrews was an empty box.