The Non-Balanced Audio Component / Multiple Outlet Landmine - So easy to Avoid...
Background - In most all homes in North America, electrical components we use are powered by a 240/120 Volt Single Phase System. The illustration to the right shows how the voltage coming into a home is split into two phases, 120 Volt Phase A in Red, and 120 Volt Phase B in Black. When you open up
your breaker box, each of those breakers represent either a 120 Volt Phase A or a
120 Volt Phase B power line. Both phases work equally well at supplying power,
so some receptacles in your home are fed power from Phase A and some are
fed from Phase B. As the illustration shows, they are180 degrees out of phase
from each other. To obtain 240 Volts, the two 120 Volt lines are combined to feed
voltage to a specific 240 Volt receptacle somewhere in your home.
The electricians who designed the wiring scheme and wired up your home did so with two essential goals - 1) make the potentially lethal voltages safe to use when we plug something in and 2) balance or distribute the power loads from the Phase A and Phase B power lines throughout the home, which is determined by how each line is going to be used. By doing so, the breaker box is more or less equally "taxed" as your home consumes power. The essential goal of balancing the two phases can actually create a conflict with the coveted audiophile desire - The 20 Amp Dedicated Line, or for that matter, anytime you have your stereo system connected to multiple outlets from different phases in the same room.
Here's why -
In an effort to provide the best and cleanest possible power, the Dedicated 20 Amp Line feeding the stereo system has been a staple goto audiophile solution for a very long time. The thinking is that if the stereo is the only thing on the AC line, the power won't be corrupted by something like a refridgerator running on the same circuit. The multiple dedicated line concept, so that each componet can have it's own power source, is an extension of this thinking.
Having multiple Dedicated 20 Amp Lines is a fine practice, which may, in some instances, yield nice improvements in the overall performance of the system, but there is also a landmine that can be easily avoided.
When your electrician is tasked with wiring your sound room with two or more 20 amp lines, his training tells him he needs to balance the power load and will typically wire one 20 amp line on Phase A, the next in line on Phase B, and alternate the receptacles from there on. The problem is that you now have some components plugged into "dedicated" Phase A receptacles and some into "dedicated" Phase B receptacles. Remember, they are 180 degrees out of phase and due to ALL of the variables involved, there will be an asymmetry to the way each Phase sine wave appears. How much assyemetry is impossible to say, and it will probably vary throughout the day. Where audiophiles run into problems here is noise. As it turns out, any deviation in how the sine wave actually appears from normal manifests as noise and harmlessly flows to the ground. Ground is something like a noise depository for the AC line. Normally, this is not a problem as lights and heating elements, or motors don't really care about the noise that is present as a result of that difference. However, with single ended stereo equipment (meaning any device that is not a truly differential circuit component), ground is also part of the music signal so ANY noise that is present on the ground will also be part of the music signal. The ONLY way to eliminate the problem is to make sure that every component is plugged into a receptacle of the same Phase, either A or B, but the same. Theoretically, those who own balanced equipment should be immune from this issue, but, I've seen instances where even the finest balanced components are affected by this problem.
To avoid this landmine, simply have an electrician come in and identify which phase the various AC receptacles in your sound room are derived and only plug your system into those from the same phase. For those who go to the length of installing the coveted Dedicated 20 Amp Line, ensure that your electrician feeds all of dedicated lines going to your stereo system from the same phase, either A or B.
It's a problem, but one that's easily avoided.
On the topic of easily avoided issues, let's look at installing an aftermarket receptacle. Please make sure to follow your local electrical code requirements. For example, the standard 15 amp feeder lines throughout your house are probably wired with a 14 gauge Romex cable and installing a 20 amp receptacle on that line is most likely against code. The reason is not that there is a problem connecting a 15 amp device into a 20 amp connector. The reason it's against code is the intended use of that type receptacle. If one were to plug an actual 20 amp electrical device into that receptacle, with the assumption it actually is a 20 amp line, and during it's operation that device drew current intended for a 20 amp service, it would over tax the 15 amp line in the wall, causing thermal stress to the Romex that is beyond it's safety margin. This could result in a fire somewhere along the Romex inside your walls. The electrical code is (usually) about safety first, and it is written to prevent devices from getting connected where they should not. Granted, there is not a problem when plugging in a 15 amp audio component into that 20 amp receptacle that has 15 amp wiring connected to it. But if a fire did occur, the fire inspectors could get you for a code violation that could conceivably void your fire insurance. And if you are selling your house, and you have 20 amp receptacles on 15 amp lines, make sure and change them back to 15 amp receptacles, just to avoid any confusion and potential legal trouble with the new owners. Or, you can avoid this problem by having 20 amp lines installed, which go famously well with those cool 20 amp receptacles!