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Guiding Current on Groundplane
Guiding Current on Groundplane
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Old 24th April 2018, 11:40 AM   #11
jneutron is offline jneutron  United States
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Quote:
Originally Posted by scottjoplin View Post
Sorry, shielded twisted pair
Ah.

STP allows two power conductors so can be quite better than coax for outputs. Just means isolating speaker ground so the shield can return all the load current.

Jn
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Old 25th April 2018, 01:51 AM   #12
Speedskater is offline Speedskater  United States
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Quote:
Originally Posted by scottjoplin View Post
Could this also mean that STP is better than coax for single ended connections?
For an unbalanced interconnect between two individually AC powered units, a coax is better than a STP as it probably will have less Common Impedance Coupling noise.
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Old 25th April 2018, 03:43 AM   #13
PRR is offline PRR  United States
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Originally Posted by jneutron View Post
Current will always try to take the lowest impedance path....... Ps. And as Cliff states, the current will divide according to some rules..
Yes, not ALL the current will take 'the lowest Z path'. It splits among ALL possible paths according to the impedances.

Current is like cars. In my neck of the woods you can take Rt 3, fairly straight and smooth, or Old Oak Road which is narrow and twisty; both connect the same two main points (employment and beer). While Rt 3 has a lot of cars, Oak is far from empty, and tends to run 30% of the traffic on the highway.

Or a water supply. Say you run three big sprinklers and a small water fountain. Water flows at all four paths. More on the lawn, less in your face, depending on pipe/hose/valve sizes.

Adding "a solid thick copper wire on the groundplane" *does* reduce the total impedance. If, in addition to Rt 3 and Oak Rd, we built a 6-lane 85MPH highway through my neck of the woods, it would not take an hour to get beer, maybe only 20 minutes. And less back-up on the roads. And easier for me to cross the road to my mailbox with the super-highway taking much of the traffic.

(Actually, traffic is a poor analogy. In electric stuff, the forcing voltage is constant or nearly so. All experience shows that if you build a road twice as good, three times as many cars show up.)
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Old 25th April 2018, 11:31 AM   #14
jneutron is offline jneutron  United States
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Originally Posted by PRR View Post
Yes, not ALL the current will take 'the lowest Z path'. It splits among ALL possible paths according to the impedances.
So far, elvee, cliff, you and I have all said this...I think we agree, no?

Edit: I think some may be confused between lowest z path and multiple paths as stated. Discussion of potential always helps.
Within a wire pair for example zip, as frequency goes up, the lowest impedance path is actually closest to the other wire. The current centroids are trying to occupy the same space, but cannot leave the confines of the conductor.
A single wire as elvee stated, if run along the chassis, will cause the chassis return current to get as close to the single wire as it can, determined by freq and impedances. Oddly enough, this will occur in the upper audio band. Bass would follow a beefier copper run.
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Old 25th April 2018, 11:53 AM   #15
jneutron is offline jneutron  United States
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What should be of interest is the magnetic fields produced by the wires. (Being a magnet man, you had to realize I'd somehow shoehorn that stuff in, no?)

If the return path is augmented such that there is a frequency dependency on the return current, then the magnetic field generated would have a strange interaction with any low level circuits, the input pair for example. Bass would couple more because the path is split, hf return centroid would drift towards the rail send (or worse,two rail sends that may not be together).
Even more complex is where the current goes during four quadrant operation, like every speaker on this planet forces.

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