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General Asylum General audio topics that don't fit into specific categories. |
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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Re: Thoughts on AC posted by alan m. kafton on February 22, 2007 at 10:37:20:
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.
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Follow Ups
- Agree, isolation is just one part of the solution. - Al Sekela 20:18:54 02/22/07 (0)
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