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General Asylum General audio topics that don't fit into specific categories. |
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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Re: Electronics 101010010010 posted by Presto on February 13, 2007 at 22:51:28:
presto: ""
Conductivity does not change with frequency as it is a function of static resistivity, conductor cross sectional area, and length of the conductor.""It doesn't? Crap, there goes my edjumakation. If y'all's gonna get all technical, conductivity is consistent as long as you stay below the terahertz range. Course, he didn't state that conductivity changes, he referred to it as a parameter as well as bandwidth.
presto: ""
"excessively high" series inductance from somewhere in the order of a few pH/ft to ?????? ""If ya's gonna lambast someone, please use numbers that are realistic. pH per foot??? Try pH per mil... A single parallel wire pair can only go down to about 150 nH per foot, and that is with zero insulation thickness.
presto: ""
WOW! So far we're doing a whole lot of juggling and playing, but you're still nowhere near a definitive explanation.""Here, I must concur. There is a lot of verbage, but absolutely no meat upon which to define a model from which a solution can be had.
presto: ""
Maybe mention ONE SINGLE ORDER OF MAGNITUDE for just a few "electrical attributes" instead of repeating the word "desireable" all the time.""Cord inductance, 180 nH per foot..cord capacitance defined by dielectric and insulation thickness..LC = 1034 EDC, assume an EDC of 10..
C = 10K/L...C = 55 pF per foot. Characteristic impedance of 57 ohms..(seems low, but I assumed EDC was 10, this implies high capacitance.)Ground loop coupling, waaaay dependent on geometry, power cord pitch..ground loop current dependent on loop resistance, amp internal coupling, dependent on how crappy the internal wiring is..star grounds suck.
presto: ""
Maybe tell us *why* a stock cords inductance is unacceptably high for most audio circuits.""Inductance is the measure of how much magnetic field is created by the current within the wire. Non constrained systems typical of parallel wire cords, spash the magnetic field outward in a dipole configuration. The more the cord inductance, the more field. One half of this field (in the upper limit) will pass between the source cord and the power amp cord. "Upper limit" includes the cancellation of the helix field, and the flux that passes outside the loop, this is not part of mutual coupling to the loop.
Given the lack of geometric control afforded any audiophile, it is not possible to come up with specific equational solutions to faraday's law of induction as it applies to the ground loop, other than to state that the coupling is proportional to frequency. Nor is it possible to generically apply Amperes law to the power cord, as pitch, spacing, and integrated total flux within the plane of the loop cannot be adequately predicted. Nonetheless, the flux will be consistent with the haversine currents drawn by the power amp supply.
It is possible to describe how to minimize the power loop effects, but numbers without controlled geometry...you ask for that which is not obtainable in uncontrolled circumstances.
Oh, btw..I would differentiate between RFI and EMI as follows:
EMI is local, and is concerned with the trapping of flux through a loop, such as the ground loop. Typical of 60 hz, as well as the low spectra for transient events like motor starts and stops. RFI I consider as a planar wavefront from a source which is not local. How either enter a system may not be clear cut..
Cheers, John
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