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Old 05-09-2011, 04:02 AM   #20
Dannii
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Join Date: Mar 2010
Location: Adelaide, South Australia (originally from Geelong)
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Quote:
Originally Posted by Analogy View Post
What does this mean in practice? I looked it up and saw some references for working with component level electronics, but say you have a laptop and a sound board etc that all want to plug in... Does this mean keeping everything on the same power strip/power outlet/circuit?
Basically, you are aiming to power all devices in your studio from one common, central point.
The idea is to avoid any potential difference along your mains wiring as much as possible. In the first diagram, the load on the mains wiring between the mains outlet and the first power strip carries the current requirements of everything on the circuit, the wiring between the first and second power strip carries the current requirements of the loads on the second and third power strips and the wiring between the second and third power strips carries the current requirements of the loads on the last power strip only.
This, combined with the fact that the total resistance of the cable to the last power strip is greater than the resistance to the first and second power strips consecutively, creates a voltage drop along the circuit leading to potential differences across the wiring and induced differential currents. When the audio earths (which are often also connected to the mains earth) between the various units are connected together, this produces a closed earth circuit known as an earth loop. If there's any induced current in the mains earth wiring, this finds it's way into the audio i/o via the common earths.
By wiring everything to a common point, this can be minimised and the earth loop currents significantly reduced.
Also, earth loops can be eliminated by breaking the loop via disconnection of the earth at one end of the audio cables. This is effectively what hum destroyers and ground lift switches on D.I. boxes and amps do.

I did a Google search and couldn't find the diagram I was looking for so I'm going to attempt an ascii version here!!!

Non star earth configuration
Code:
Mains------power strip-----------power strip---------power strip
             |    |               |       |                |
             |    |               |       |                |
           DAW   Synth          Audio   Amplifier       FX rack
                              Interface
Star earth configuration
Code:
                                Mains
                                  |
                                  |
                          Synth   |  FX rack   
                             \    |    /
                              \   |   /
                             power strip
                              /   |   \
                             /    |    \
                           DAW   Amp   Audio
                                      Interface
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Last edited by Dannii; 05-09-2011 at 04:09 AM.
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