The level that a power cord will affect a component or entire system is dependent on several factors:
1) The design of the component. Is the product prone to changes in impedance at the source of the power supply ? This can also effect how much electrical "trash" the component can put back INTO the power line.
2) How "dirty" the AC coming into the system is. After all, someone that is living in a large building with TONS of circuitry coming off of one main ( ala a condo, apartment building, hi-rise, etc ) will tend to have more noise to deal with than someone that lives out in the country with minimal draw from their specific pole transformer.
3) If you are using some type of PLC / filtering device in conjunction with aftermarket power cords. Using two different types of devices can either compound the benefits of each in an additive manner, neutralize each other or produce poorer results than a standard cord. One filter ( i.e. power cord ) put in series with another ( i.e. Power Line Conditioner or "PLC" ) can actually "detune" the performance of one or both pieces. On the other hand, you might also end up with something that compliments each other and offers greater performance than either could on their own. As usual, trial and error is about the only way to find out. I'm working on a way to measure various combinations and chart the results.
4) The overall design of the cord in terms of geometries, shielding, impedance, gauge, etc... Obviously, some cords will work better when used within a specific power range than others. In my opinion and given equal designs, you can't have too heavy of a power cord ( short of it weighing too much and making it difficult to work with ). Any reasonable sized power amp should be run with at least a 14 gauge cord at minimum.
5) How good of a connection is made between the cord and wall socket and then again where the cord plugs into the component. This can also be carried back into the cord itself and how good of a connection is made at the IEC and male plug internally.
Having said all of that, i have noticed differences by using various power cords. This is true even though i used to be of the most vocal proponents of the "there is NO way that a power cord could change the system so long as it is not current limited" school of thought. I was wrong and ran my mouth even though i had never tried various designs. Quite honestly, i found the idea preposterous at one point in time. That episode alone taught me a lot and i know better now. Sean
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