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In Reply to: Thoughts on AC posted by Al Sekela on February 22, 2007 at 09:39:31:
Great, practical advice Al, but....A separate dedicated circuit for each component seems like drastic overkill, but is actually a cheaper way to isolate the components from each other's power supply noise than exotic plug-in filters.
....does absolutely nothing for VHF and UHF noise riding on the "juice".
Follow Ups:
Everything Charles Hansen says is true and apt, but his experience is limited as he reports in one of his posts.Separate dedicated circuits remove the lower-frequency coupling that comes from multiple audio equipment power supplies sharing the same power circuit impedance. Filters that can effectively reduce this coupling after the outlet are large and expensive. Filters and other techniques that reduce the effects of UHF noise do nothing for the baseband coupling problem.
Having multiple dedicated lines installed is relatively inexpensive as long as the routing space is easy to access and there is capacity on the breaker panel. It costs about the same amount to have the electrician show up to do one line, and the additional material costs are a reasonable increment.
Here are some of the other issues with AC power to revealing audio systems:
The power circuits themselves resonate, just as power cords and audio cables do. This can be tamed with damping filters (such as Quiet Lines), either R-C networks directly across the line-neutral, or on the secondaries of lossy transformers. In either case, equivalent R should be about 120 ohms as seen by the line and C is whatever X- or Y-rated capacitors you can find that are not magnetic and that include very small values. Multiple R-C networks, with different values of C spaced in decades, work better in parallel than multiple parallel C in series with a single R. Wire them to unplated two-prong plugs, and pay attention to safety if the resistors are not flame-proof. It takes trial-and-error to find the best places for these filters in the house.
The AC safety-earth wiring carries RF noise and pollutes the audio ground in equipment that has the case or chassis connected to AC safety-earth. Charles Hansen has resolved this issue in Ayre equipment by using double-insulation. For everyone else that has grounded gear, a fix is to break the ground loop for small voltages by inserting antiparallel rectifier diodes in series with robust inductors in the AC safety-earth loop. This is a WWII-era radio amateur trick, and has been commercialized for the pro audio world by eb-tech:
http://www.ebtechaudio.com/humxdes.html
The diodes turn on and conduct fault current to maintain safety. However, this device does not contain inductors. Diodes have capacitance, and will conduct higher frequencies.
This tweak works also when applied to noise sources, such as UPS devices, appliances with computer control, DVRs, etc. You may need to add a 1000-ohm resistor in parallel with the diode pair for equipment with ground sense circuits. Surge protector strips that contain RFI/EMI filters couple noise to the AC safety-earth from the hot and neutral, even if the appliances plugged in to them are only two-wire. This tweak is effective on these devices.
Standard AC duplex outlets mounted in steel boxes comprise single-turn transformers coupled to the AC power. There is a conductive path made of steel that threads the hot and neutral wires. Not only is the steel hysteresis a problem, the box is also connected to the AC safety-earth. It helps to break the path by installing a Nylon screw and washer at one end of the outlet. This should also work for audiophile outlets, even though they are made of brass or bronze and not steel: the box is still steel. Also, avoid magnetic stainless steel cover plates.
See my post on the Cable Asylum for a comparison of some audiophile outlet devices. They do indeed make for better sound.
Untrue if you are talking about noise internal to the audio system in question which are all by definition part of this dedicated set of lines. Of course it is true if you mean line transients from outside the equipment on the dedicated lines like say your clothes dryer motor or something. It isn't quite clear what you mean.An example to illustrate the point. Switching power supplies will cause voltage ripple on the power grid due to finite power grid output and line impedance. These supplies can produce harmonics into the VHF or UHF range and above. Any device in parallel with this device on the AC grid will "see" the voltage transients that these power draws cause(at switching frequency) at a level equal to the amount of impedance of any shared conductor (supply and return path) length times the current being drawn each switch cycle added to the voltage surges or sags due to imperfect power grid voltage regulation. By running dedicated lines one achieves the goal of sharing less of the current path between components and has thusly lowered the ripple seen by devices on seperate legs of this dedicated wiring scheme.
Digital and video gear radiate noise within the system, and without. Al alluded to filtering digital gear because of these contaminants. But as Charles Hansen mentions in another thread, there are many electronic products (outside the audio/video system) that transmit and radiate noise as well, and these noise contaminants are not carried via the line, but through the air. A dedicated wiring scheme will not address those particular problems....hence my statement.
"there are many electronic products (outside the audio/video system) that transmit and radiate noise as well, and these noise contaminants are not carried via the line, but through the air."Again, not true. In reality all electronic devices that have accelerating charges within them will have radiated and conducted emissions which are undesirable and unintended. It is merely a question of scale. As I pointed out there are conducted transients caused by switching power supplies that are back fed into the AC power grid. This is precisely why these types of equipment must go through conducted AND radiated portions of compliance testing in order to get the various CE and FCC marks of aproval.
Rereading Al's post I don't think it is safe to assume that he was even referring to radiated emissions. In fact I am interpretting his post to mean conducted since I believe Al is with it enough to realize that line filters or dedicated lines won't do anything for blocking spurious radiated emissions energy and in that context his post makes perfect sense.
Again, not true.I suggest reading Charles Hansen's posts in this very thread. He stated some of the facts (and circumstances) very clearly.
What's he saying got to do with me disagreeing with your original statement about it not being possible to reduce effects due to conducted emissions in the VHF and UHF bands with dedicated wiring?It appears that Charles post addresses other potential noise sources besides conducted emissions on the grid. Fine, I don't disagree with anything he's saying. Does it mean he's saying or that it is a fact that there is no such possibility of these noises I speak of? After reading his post over and over at your recomendation I really don't think Charles would say those things. No man it was you whio I was disagreeing with. But that's not my point. My point is that conducted emissions from audio equipment exists and for equipment with poorly filtered switching power supplies this conducted noise can be really bad. Even properly designed and functioning equipment will have some level of undesirable conducted emissions even if it is within the limits of the local regulatory groups and laws. It's just the unavoidable physics of the chosen techs at this time. Dedicated wiring will reduce the effects of these conducted emissions. Please see my previous explanation.
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