Well, like Rob Watts, whose insights are scattered in the Head Fi forums, John Swenson's insights are scattered throughout the Computer Audiophile forums so you'll have to search for them to read them. But here are the highlights I am quoting from him, in addition to what he wrote on the uptone page. They are coming from numerous posts on numerous forums over at Computer Audiophile:
But what I am talking about [leakage current] is the loop that forms through one PS to its DC output through a device (usually the negative, but it can be the positive) through an interconnect,(again usually the ground or shield) (digital or audio) to another device, through ITS power supply and back through the AC line to the first power supply. This is a low impedance loop in normally connected systems, usually less than an ohm through everything.
What I am talking about is very low impedances, small voltages and small currents. It has nothing to do with earth ground, safety ground etc. It is formed by capacitances in the PS between AC line and DC output generating a voltage between AC line and DC output. When a low impedance connection is formed between the DC output of one PS and the DC output of another PS these voltages form a current flow. Since the loop (I'm calling this a leakage loop) goes through TWO power supplies the waveform of this leakage current depends on the characteristics of both supplies. Thus it is hard to define the characteristics of a single supply, unless you define a "standard" supply to reference all others to.
You can get rid of the noise generated by these loops in two ways, block the loop somewhere in the loop (The LPS-1 does this for certain paths), OR decrease the impedance along the loop, if the impedance is lower the NOISE generated by the CURRENT will be less.
To decrease the impedance on the AC you need to have the lowest possible amount of wire, filters, anything else between the outlets you plug your AC cords into. This specifically means NO filters in the power strips, they dramatically increase the leakage currents between boxes plugged into such a strip.
Ideally you should have ONE power strip with EVERYTHING in your audio system plugged into that one strip. By everything I mean everything that has an AC plug that is connected into your audio system somehow. This includes power amps, computers etc.
Yep, all AC line to DC power supplies (except LPS-1 and LIO) have leakage current, even ones in pre-amps and power-amps. LPS supplies generally have lower leakage than SMPS supplies so the effects of the LPS in pre/power amps is usually less than the leakage current involving digital systems which usually use SMPS. It is the almost universal use of SMPS in computer systems and the larger leakage current from such supplies which have made leakage current much more important to SQ than the leakage current in the rest of the chain.
