At the normally low [DEL]DC[/DEL] offsets involved between two separate grounding points, the current will only flow through your body if you are offering a [DEL]better[/DEL] path to equalize the potential, which means you need to be touching *two* different "ground" sources. The metal parts of your bass will be one, and the other could be a microphone or the stage itself.
Just in case, I always recommend rubber-soled shoes to block current from flowing from your instrument to the floor. If you are isolated from Earth ground with rubber-soled shoes, you should not be able to get a "shock" by touching only your instrument. Now, of course, if you simultaneously touch something else (like a microphone) then all bets are off again.
I have been shocked by a ground-differential like this before, so it's definitely possible. In my case, I rested my right hand on the metal case of a piece of equipment which was connected to an old two-prong electrical circuit (where the neutral is grounded at the panel in the unit), and with my left hand I grabbed a coax cable from the wall (which was grounded across the street at the cable utility pole). At that point, my body was the best path to equalize those two different potentials. Zap. Very uncool and unpleasant. I had to get a coax ground isolator to fix the problem. I used a cheap one which doesn't have the balanced transformers, and so I had some signal loss as a result.
In any case, I completely agree with the ground isolator solution. If that fixes the problem, you're all set.
Of course, it's also a remote possibility that the shock you got is due to a reversed neutral, which is very dangerous and has caused fatal electrocution on stages before. I say remote because most outdoor circuits since the 1970s have been required to be set up on GFCIs, most of which won't operate at all on a reversed-neutral (and would have tripped anyway in your case). But if ANY of those outlets supplying your interconnected gear are without GFCI protection, then you really should watch out and test those outlets for reversed neutrals just to be safe. The testers are cheap and available at any hardware store.
Just in case, I always recommend rubber-soled shoes to block current from flowing from your instrument to the floor. If you are isolated from Earth ground with rubber-soled shoes, you should not be able to get a "shock" by touching only your instrument. Now, of course, if you simultaneously touch something else (like a microphone) then all bets are off again.
I have been shocked by a ground-differential like this before, so it's definitely possible. In my case, I rested my right hand on the metal case of a piece of equipment which was connected to an old two-prong electrical circuit (where the neutral is grounded at the panel in the unit), and with my left hand I grabbed a coax cable from the wall (which was grounded across the street at the cable utility pole). At that point, my body was the best path to equalize those two different potentials. Zap. Very uncool and unpleasant. I had to get a coax ground isolator to fix the problem. I used a cheap one which doesn't have the balanced transformers, and so I had some signal loss as a result.
In any case, I completely agree with the ground isolator solution. If that fixes the problem, you're all set.
Of course, it's also a remote possibility that the shock you got is due to a reversed neutral, which is very dangerous and has caused fatal electrocution on stages before. I say remote because most outdoor circuits since the 1970s have been required to be set up on GFCIs, most of which won't operate at all on a reversed-neutral (and would have tripped anyway in your case). But if ANY of those outlets supplying your interconnected gear are without GFCI protection, then you really should watch out and test those outlets for reversed neutrals just to be safe. The testers are cheap and available at any hardware store.
