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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: DIY version of AudioPrism quietlines? posted by cporada@cabnr.unr.edu on December 16, 2006 at 16:02:33:
As I understand them, the AudioPrism QuietLines are simply capacitor-resistor filters that damp the AC power wiring resonances. However, capacitors connected to the AC line can be damaged by voltage spikes, and the damage can cause them to catch fire. The resistor may also catch fire if the capacitor fails to a short-circuit.This makes it necessary to use X- and Y-rated capacitors, or to use fire-proof housings. See the link for more than you ever wanted to know about X- and Y-rated capacitors. In brief, the X-rated types are for use from line to neutral, where failure to a short-circuit would result in the fuse or circuit breaker opening. The Y-rated types are for use from line to ground, where the capacitor should only fail to an open-circuit because failure to a short would threaten life.
To avoid confusion, the linked paper refers to use of capacitors directly across the line. Adding a resistor in series, as AudioPrism does, makes the filters more effective, but complicates the safety discussion.
The X-rated capacitors can be found in sizes up to 1.0 microfarads, while the Y-rated caps are much smaller. This makes it impractical to limit your filter to Y-rated caps only, although this would reduce the safety concern.
Using a single R-C pair limits the effective frequency range. Adding more R-C pairs in parallel, where Rs are about 120 ohms and the values for C are in a descending series, such as 0.47, 0.047, 0.0047 microfarads (or similar values: exact decadal sequence is not important), gives a broader frequency range for the filter. If you have a surplus parts store, look for capacitors with the X or Y designation, a voltage rating of 250 or higher with a tilda (~) to indicate that is an AC rating, and that are not attracted to a magnet. Steel parts inside these components do add colorations to the audio system.
Flame-proof resistors are the safest, but you may not be able to find any without steel parts. Half-watt is OK for 1 microfarad or less on 120 volts, 60 Hz.
To connect the filter to the outlet, use cheap, unplated molded plugs cut from dollar-store two-wire extension cords. Plated plugs introduce their own colorations, I have found.
I would not do anything to filter line or neutral to ground. Dumping noise on to the ground seems to cause more trouble than any damping action benefit. BTW, I believe this is partly why common AC inlet filters give poor performance with audio.
Again, safety is paramount. Even the X- and Y-rated caps used in TV sets cause several house fires in the USA each year. Make sure that your filters cannot set anything on fire if they should fail.
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Follow Ups
- Use extreme care with direct AC exposure! - Al Sekela 14:09:17 12/17/06 (1)
- Re: Use extreme care with direct AC exposure! - Sean 23:13:16 12/23/06 (0)
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