In response to our thread on ground loops (see inSync 3/12/99 & 3/4/99) one reader writes: “Another solution might be to install GFI (ground fault interrupt) circuit breakers or outlets in the studio, enabling the safe use of two prong adapters. These cost $10 per outlet these days, and virtually eliminate any possibility of losing one’s life because of an electrical short. Don’t know why these are not more widely used…”
In general we are advocates of GFI. However the hyper-tweaky out there might say that the current sensing component in them might somehow subtly change the behavior of connected equipment. Not a big deal in most circumstances, but we all know that audio issues can get pretty minute. We’re not THAT picky, however, and we think they are fine.
The problem is that this is still somewhat of a band-aid. Lifting AC grounds can get rid of the most annoying hums, but there may still be other ground loops in a system. Further, it takes away a good ground connection that can act as a shield reference (or technical ground) for equipment. Besides at $10 a pop it can still get expensive, and who’s going to install them?
Saying all that, the method certainly can work and we don’t have a problem with someone going that way. However we still prefer the method of lifting shields at one end of signal cables. In the 3/12 issue of inSync we talked about using transformers as a way to isolate unbalanced equipment grounds. Another less costly trick for unbalanced cables is to use two-conductor shielded cable (balanced cable) and use the second conductor as the sleeve or ground connection. Then attach the shield at one end. A well-grounded shield that does NOT have current flowing through it is a very good way to prevent ground hum that gets induced via EMI. If the shield were connected at both ends it would then have current flowing through it and induce the hum into its cable. Now technically a ground loop still exists in the grounded side of the signal cable that is connected, but we’ve found in practice that on the relatively short runs of unbalanced lines the separate non conducting shield is often enough to ward off problems. Your results may vary. We told you there a myriad of possibilities for studio grounding and shielding. We’ll have even more about this in the future.