What determines whether an input jack needs to be insulated from the chassis or not? For my standalone preamp/reverb/vibrato thing, I'm insulating the jacks that connect to the effects loop send and return to avoid creating a ground loop between the amp and the standalone thing. The input and output jacks ground through a ground lift circuit, that does connect to chassis ground, but there's no direct connection between the loop jacks and the chassis. But as yet, I don't have insulating shoulder washers on the direct instrument input jack. Do I need to?