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In Reply to: Do this search posted by bartc on March 26, 2007 at 05:44:45:
Thanks for the help. I have another question, however. Why does Al recommend having the resitor in series with the caps while Magnan says the resistor should be in parallel to dissipate the charge from the caps when unplugged? Sorry if this is ignorant, but it seems to be an important difference and I don't know enough about AC power to understand the difference of opinion
Also, can one use normal resistors, or is there some special type people like for this application? I known Al recommends PRP resitors for the speaker R-C filters, but for AC I don't know... Thanks
Chris
Follow Ups:
The QuietLines approach is to use a resistor in series with a capacitor. The purpose of the resistor is to dissipate the energy in RF noise on the AC line, and the purpose of the capacitor is to keep substantial 60 Hz power out of the resistor.The AC line acts like a transmission line with approximately 120 ohms characteristic impedance. If you terminate such a line with a low impedance, which is what the Magnan tweak does, RF noise will be reflected from the filter and go somewhere else to cause trouble. If you terminate it with a 120-ohm resistor, then the noise will stop at the resistor, but you will dissipate a lot of 60 Hz power in the resistor (120 watts). By using a series capacitor of the correct size (say, one microfarad or less for half-watt resistor), the RF noise will be dissipated but the 60 Hz power will be kept to a quarter of a watt or less.
A very large capacitor may retain a powerful jolt if it is disconnected from the AC line at just the right instant. This is why Magnan recommends a shunt resistor to dissipate any remaining charge. The stored charge in a small cap will be small and IMO you do not need a shunt resistor. It will not hurt to have one, however.
The capacitors must be X- or Y-rated to avoid a fire hazard. Even with an X-rated cap, however, you can get a short-circuit failure. This would cause the resistor to burn out. A non-flame-proof resistor will burst into a flame about the size of a kitchen match, so provide a suitable fire-proof housing if you do not use a flame-proof resistor.
Hi Al
Thanks for the very helpful info. So a good starting point to make a filter for the input to my CD player could be [a 1uF cap perhaps bypassed with a 0.1uF cap placed in series with a 1/2 watt 120ohm fireproof resistor] between the hot and neutral line? Does it matter which line is attached to the resistor and which to the capacitor? I seem to remember for your recommended speaker R-C filters there was a directionality, but I don't remember which way they went.
Thanks again
Chris
Also, you might want to use some smaller caps as well, with a separate resistor for each. You can get Y-rated caps at very small values, and these are safer than X-rated types.
You'll have to ping Al for the theory. Not my department!I use the flameproof resistors you can buy pretty much anywhere. It's a safety issue.
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