Thursday, February 14, 2013

Star Grounding

This post is part of a series on eliminating noise from audio systems. Click Here to see them all. 

I've got one last trick for beating hum and noise and this comes in particularly handy for guitar players but it's just as important to keep in mind for other applications sometimes too. Everyone knows that grounding is important. Unfortunately those paths for electricity to exit the building safely in case of a "leak" aren't always our friends when trying to keep noise out of audio circuits. That can lead to people lifting the safety ground on equipment.

Let's be clear. It's not just stupid, it's straight up illegal in some instances. So just don't do it. Ever. 

Lifting the ground on a direct box or other audio path is the way to go when you're trying to get rid of common mode noise (ground loop hum). But in a system that's not balanced audio, like a guitar rig, you can't lift the ground and still have signal. It would seem that there's nothing left to be done, but there is.

When you plug in a guitar rig, on stage or in the studio it should be on the same "leg" of electricity as the rest of the audio gear like we talked about in the last post. That alone can kill off a ton of noise. But if the amp and say, the pedal board are plugged into the same circuit but from different outlets, the two devices can be at different ground potentials and that's when Buzz Lightyear shows up as an uninvited guest. 

So here's your method. Run a power strip or other splitter from the point where you're plugging in. Plug the amp into that and then plug an extension cord for the pedal board on that same power strip. What you end up with if you do this for every series of devices in the setup will look like a star if you draw it out. Panel to outlet, outlet to first device, first device to second device. Even using two outlets on the same circuit won't be as clean because you're going panel to first outlet (where the amp is), on to second outlet (where the pedals are) and then you've got a loop once you introduce an unbalanced guitar cord into the mix.

But wait. Aren't the two examples the same? Just taking a different route to the same destination? Yes, that's the key. Physical location. If the power and the signal for the pedal board are traveling roughly the same path through the room they'll be subject to roughly the same interference an have closer to identical ground potential when they arrive. A guitar cable running across a stage and an electrical circuit running through a wall in a conduit are having different experiences before they arrive at that same destination.

I know it might sound complex or like it might just be one more of those voodoo superstitions that abound in this industry but it works. I've had guitar players at their wits end, especially guys with single coil pickups go to this method and it has saved the day time and time again. Even with all the hand built, triple shielded, impedance matched, tone molecule preserving cables, just plugging in the power the right way can make a world of difference.

So there you go Brethren of the Knob and Fader. This concludes our impromptu lesson on how to kill noise on stage and in the studio. Go forth and prosper (and no humming on the way out!).

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