I'm not a big fan of piggyback filtering, the big problem you run into is over saturating the smaller of the two circuits. In most cases audiophile PLC's are nothing more than a simple .1uf or .47uf x-cap across the load at each receptacle with a possible parallel surge circuit. Single value designs are fine if you only use a few of the same cap value, but it can quickly become a problem if multiple devices installed together use the same ringing value. The fine line is trying to prevent a crosspoint in the harmonic bandwidth that causes too much of a roll off / suckout at any one frequency. The basic PE circuit covers multiple frequencies, that is how we avoid rolling of harmonics.
In your situation, I probably advised against plugging the S/AC into the PLC because of the strength of the PE circuit, and maybe there was some reason you may have brought up as to why the wall install was bad for your set up, and I may have said try both and see which sounds best....that is my basic line, I give that same advice to everyone. I probably also said the S/AC was the smaller of the two V circuits, S/AC and Pro, and the S/AC would do less saturation harm if you decided to plug it directly into the PLC. In my opinion the S/AC should always be placed at the wall when other brand PLC's are involved.
Was there a reason why Jen recommended the standard PE vs. something larger like the S/AC for the APC installation? Was budget an issue? We normally recommend the standard PE as an intro in the product line, and in this case a pair of filters should have tuned the APC with no problems, but that doesn't mean the circuit tuning process should stop, a standard PE only provides -6db of acoustical noise saturation...2 filters provide -9db's, 4 filters -12 db's, etc. On my web site, as well as this post, I have a tuning guide to show our clients how to get the most out of the PE concept. Once the client experiences the potential, the tuning concept is usually the next step. But as I have stated prior, harmonic control and elimination requires a multi-prong attack strategy, all circuits must be addressed by filtering all offenders, each component needs to be filtered, isolated, and working at maximum potential.
1. A power supply is a funny thing, it's designed to filter incoming noise and convert a/c to d/c...it sounds simple enough, but electrical theory 101 is never simple. All power supplies are able to operate +/-5% of a perfect voltage spec, meaning in the US it should be 120v, Canada is 117v, Europe is 220v, UK 240v, etc. Operate means exactly that, able to function, but not able to filter. +/- swings of voltage cause added resistance (119v-) and added inductance (121v+). Both of these issues create odd harmonics in the form of mechanical noise and saturation on the circuit when component A is plugged into the wall. Most people have heard added resistance before, it causes the uppers mids to become edgy, while it thins out the mids and lower treble. Too much inductance causes soft bass, maybe one note bass, and oversaturated lower mids. The example only shows what could happen to one component as the x-caps in the PI-choke inside the component start to leak on the neutral, it creates a magnetic mess inside the multiple connected wire geometries. Sometimes we can alter the magnetic build up caused by the leakage by altering the wire geometry of the main power cord. Some cables are designed to increase the inductance to offer a warmer sound, and others are designed to boost capacitance or flatten capacitance/inductance levels creating a flatter/more open sounding cable with increased articulation and top/bottom extension. Either method is fine as long as it matches the particular situation. In most cases people play a mix and match game based off recommendations and band-aid solutions in order to control line harmonics. The idea and design of the PE circuit takes this into consideration, we thought if we could alter the line frequency created by the voltage/power supply interaction, we could provide a level playing field for multiple components to be installed without leakage contamination (crosstalk distortion) creating multiple odd harmonics between the installed power supplies. As you know, no two manufactures use the exact same power supply design and they all leak back the circuit at different ringing frequencies. Then take into account tweaks and all the other crap we use to alter the sound of the component and you now have a mess on the circuit. The strength of the PE overpowers the component frequency and tunes each component, assuming they are all PE filtered, to one perfectly tuned frequency, which is ruler flat of all harmonics up to a specific frequency (pending model). All odd harmonics are now controlled in db level to remove peaks and dips, re-pitched/re-tuned based off circuit spec, and working as one. Pending the model filter the customer selects, the filter can provide total PFC, act as a surrogate tuned power supply, enhance parallel line filtering, and eliminate the cable interaction from the equation.
2. Distance specs are not really put out there for audiophiles to ponder over, what they mean to me is that I can plug a filter 3500 feet away from the stereo system and still enjoy the sonic benefit of the parallel method. That is what I mean when I say 250, 1000, 3500 feet from the source, in a studio where multiple circuits are in use, I can plug a filter into circuit A and hear the benefit on circuit G with 400 feet of Romex in between with multiple circuit breakers in the loop without loss of signature sound. In a Pro application, which is my primary business, those specs mean a lot if you are tuning a mastering facility or something along those lines.
3. Stabilization has to do with how the line/circuit deals with ringing frequencies. Power supplies adjust rather quickly, but magnetic fields on the circuit that are being disrupted by added capacitance usually collapse, build up, collapse again, build up, and so on for each injected frequency, the filter size / leaked capacitance will determine the time of adjustment. As for the filter, all PE circuits are fully charged within the first 12 hours. The circuit on the other hand, that is designed to handle 20A and 25A continuous load, are usually used way under continuous wire spec, because the circuit amperage demand is so low it takes the magnetic field between the hot, neutral, and earth longer to build and stabilize. In most cases 10 to 12 days is required for a PE on a 20A 120v circuit. Over here in Europe (16A 220v), where 16ga x 3 is spec, I can have a circuit stabilized in 60 to 72 hours.
