Re: Complete the DC circuit?
If you don't have any safety ground from the mixer or amp rack, then your local "ground plane" really isn't earth grounded and could become dangerous at any time. I think you should consider making your own "grounding plug". I built something like this 30 years ago while playing in rat-hole clubs that had no grounded outlets in the wall. Instead of putting up with the shocks on stage, I built a simple grounding system which consisted of a pair of vice-grip pliers on a 250 ft spool of 10 gauge wire terminated on a lug connector. Since there were no outlet grounds to be found, I ran the "ground wire" vice-grips to a cold water pipe in the basement, then connected the ground lug under a screw on the metal body of the mixing board. Since the XLR shield connected the chassis of the mixer to pin-1 and the chassis on the power amps, everything was safety grounded. Now, this wasn't the best grounding system in the world, and not exactly to code, but it worked quite well.
For your situation, you should already have grounded outlets, so you either need to bring your own Edison-Euro power cable with an intact ground pin, or come up with a kludge cable that will get the safety ground of the wall outlet to the chassis of your mixing board. I'm guessing that the house "engineer" got tired of ground loop hum and simply cut off all of the power cord ground pins, which is not only illegal, but a serious safety issue for the performers on stage. I do know you don't want to make too many waves with club owners since they'll find another band who's willing to put up with the shocks, but that just perpetrates the assumption that getting shocked on stage is OK, when it's not really safe.
Contact me directly at mike@fitsandstarts.com if you want some pointers on how to do this.
