Originally Posted by bri1270
If you have two different outlets going to two distinct panels, (one in the basement and one in the garage) each with their own ground, could you still get a ground loop? I'm guessing yes, but I'm not sure.
For the purposes of this discussion, a groundloop is defined as:
Any physical loop of conductor which is able to trap magnetic field within the loop, and generates voltage as a result of that magnetic field changing it's strength over time. This generated voltage is defined by Faraday's law of induction (for all the geeks).
A loop which somehow taps into a change in voltage potential caused by a current.
First, the magnetic field thingy.
A generator works by changing the magnetic field within a loop or loops of conductors. They do this by rotating the loops or the magnets.. The crux is, the field is changing and it induces a voltage. If the loop is closed, like a ring, currents will be generated.
If you have two three prong devices, an amp and a source, and plug both into one wall outlet, you still form a loop
.. Between the grounds. If you space the two cords as far away from each other as possible, the ground loop can pickup external field noise. This can be motors, lights, dimmers..or, indeed, the loop can pickup the hum caused by the poweramp current. This can be 60 cycle, or it can be haversines.
Bringing the two cords closer, that reduces the total loop and it's sensitivity.
In one of my apps, I have an amp type QSC RMX 1450 on stage, and a simple numark mixer in a balcony 100 feet away (as the cord flies). I feed this amp using single ended line level runs
, not balanced.. To keep hum and noise down, I wrap the line level runs around a 100 foot extension cord. This cord powers my mixer/cd set. With tens of kilowatts of lights in the house on dimmer, the house A/C, a toro 700 leaf blower on stage, and a 250 kilovolt vandygraf on stage, there is no induced noise in my system. (this drives the audio guy here nuts, he uses rf's, DI's, balanced, and xfmrs..)
Ground loops of this nature will cause shield currents in the IC's. While this in itself is not very bad, most amps are not designed to ignore this, even differential inputs.
IR drops, what would you expect of a house?? In fact, chances are you have a voltage gradient on your property caused by the power company.
This discussion also pertains to 2 wire setups, but the path the currents take is not so obvious since neutral/not is the only thing involved.