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In Reply to: One conditioner may not do everything you need. posted by Al Sekela on March 18, 2007 at 14:21:05:
>>"If your audio components use three-wire plugs, then this pollution affects your sound at low levels, even though you have a dedicated line. There are tricks to deal with this, but not widely posted on the AA."<<Hi Al... I wonder if you could point/share with me a link or post that will enlighten me on this subject ...
Follow Ups:
Audio components use two- or three-prong plugs for USA applications. The third prong is the connection to the AC safety-earth wiring. This wiring is designed to carry fault current for as long as it takes to trip the circuit breaker or blow the fuse, without allowing the exposed metal on the appliance to reach lethal voltages, in the event of a power fault inside the appliance (hot in contact with case through breakdown of wiring or insulation).The safety-earth AC power wiring is separate from the neutral, but is connected to the neutral at the AC power distribution panel. Both of these conductors are tied to an earth connection at this point, as part of the standard practices for how power is brought into the home.
Unfortunately, this connection is called "ground," and the safety-earth wiring is commonly called the "ground" wiring. This causes endless confusion for audiophiles, as audio circuits also contain reference points called "ground" by the designers. Many audiophiles think that the safety-earth "ground" is some sort of magical sink for noise because it shares the same name as the zero-voltage reference point in the circuit.
In reality, "ground" is a convenient fiction, both for AC power and for zero-reference in circuits. Many circuit and/or layout designers fail to account for the impedances between different tie points that are labeled "ground" in their schematic diagrams. In digital circuits on chips, this leads to mysterious bugs. In audio circuits, this leads to noise pollution among other things.
Audio components with metal cases that are attached to the AC safety-earth have some degree of coupling from the case to the audio zero-reference. In some examples, there is a deliberate attachment at one point. In all examples, there is some amount of parasitic capacitance distributed throughout the internal works.
The AC safety-earth wiring is designed to work at 50 or 60 Hz. It has long extension and high impedance to much higher frequencies. Any RF noise that gets onto this wiring will go throughout the house and be present at all outlets, even though the safety-earth wiring is firmly attached to the earth at the power entrance point.
This noise will be coupled to the audio circuit through the parasitic capacitances or direct ties within audio equipment where the case is tied to the AC safety-earth. The noise will not be audible when there is no signal present, but will affect the audio signal by adding spurious tones that mimic natural harmonics.
In systems where multiple pieces of gear have the safety-earth connection, there will also be a "ground loop" which can cause audible hum when there is no signal present. This "ground loop" shares some of the connection and coupling artifacts with the safety-earth noise problem, but is independent. It is possible to have a silent "ground loop" but still have safety-earth RF noise, as I have found by experience.
So-called "isolation" transformers do not eliminate the safety-earth noise problem, as both the primary and secondary windings are attached to safety-earth. These transformers do absorb normal-mode noise (that exists between the hot and neutral) and common-mode noise (where hot and neutral act together), and this can be beneficial to some audio systems.
Typical RFI/EMI filters, as found in many non-audio appliances and surge protector power strips, couple the hot and neutral lines to the safety-earth with small capacitors. They actually make the safety-earth noise problem worse, as they can take normal-mode noise and couple some of it to the safety-earth.
The uncommon tweak I've found to reduce the safety-earth noise problem is to insert rectifier diodes wired in anti-parallel into the safety-earth lead. The diodes are selected to handle the fault current. They have the property of exhibiting high impedance to very small noise voltages, but low impedance to large fault currents. I've intalled them in my audio system and wherever I have filters on non-audio appliances that generate RF noise. They've given me a much lower system noise floor and allowed my system to produce more natural sound.
Can't thank you enough for your time and explaination.I just need to sit down and go through this slowly.
Would you wire this R/Diode at the main panel saftey ground between the safety bus bar and the lead to the ground rod or ????
Also what value/size R/Diode and any special type.
Don't mess with the house wiring.My power cords are home-made, so I don't mind modifying them. If you have fancy power cords, you can experiment by making some short extension cords and placing the anti-parallel rectifier diodes in the ground lead. This kind of thing is also good for experiments with non-audio appliances that make electrical noise. Some devices, such as UPS for computers, have ground-sense circuits and will not work with the diodes themselves. In this case, use a 1000-ohm non-magnetic resistor to shunt the diodes.
The rectifiers I use are in 4- or 6-ampere bridges I get at a local surplus electronics store, simply because they are cheap and they do not have single rectifiers of appropriate sizes. Wire the input leads together to make one terminal and the output leads to make the other. This gives two anti-parallel pairs in parallel.
The diodes do not see reverse bias, as one would always be forward-biased in a fault condition. However, the diodes have capacitance, which allows some RF noise to get through. Diodes with higher reverse-bias ratings have less capacitance for the same forward current rating. Therefore, use the highest reverse voltage rating you can find.
I've tried HexFRED diodes and did not like the result. I believe these have more capacitance than conventional rectifiers of the same rating.
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