Stereo guitar into fender tube amps and octave down signal to an ampeg solid state.
Also running vocals through the unit.
Extreme noise as expected, so I ordered 2 transformer based isolators, plus one for XLR.
Had the isolation box running both fender amps still some significant noise, albeit much better, and even isolating the vocal chain for the first time I felt electric shock on the mic, which freaked me out.
Swapped one ground lift from one fender to the Ampeg and for some reason… WOW noise went down significantly, and no electric shock on the mic.
Question, is it wise to get another transformer isolation for the remaining amp, theoretically completely isolating ground?
Rule of thumb is you need the number of amps -1 isolating transformers. The QC should be grounded to only one of the amplifiers, using the ground lifts or isolators to float the other grounds (i.e., grounding the shielded cable at the other end). QC needs a ground, but it should get it from one place and be isolated from other connected devices to avoid ground loops.