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Old 2nd March 2013, 10:55 AM   #21
AndrewT is offline AndrewT  Scotland
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Originally Posted by argonrepublic View Post
Can I expect any immediate improvements using X2 capacitors across my AC line? ........................
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The primary purpose of an X2 capacitor across the Live and Neutral of the Mains supply is to attenuate the interference .....................
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Different issue..................
Is it a different issue?

reducing interference can have a very audible effect.
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Old 2nd March 2013, 11:49 AM   #22
DF96 is offline DF96  England
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Maybe not a different issue. When people talk about putting X2 caps across the mains I just assume they are talking about low value caps inside the equipment. Mostly this is what they mean. Putting big caps across the mains outside the equipment is not something I would do, so perhaps I forget that some people encourage this.

If a mains filter is needed then a mains filter may be the best option. Simply slapping on a big cap and relying on wiring inductance seems a bit crude. As I said, it could increase induction of noise because it increases the noise current in the mains wiring.
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Old 11th March 2013, 11:47 PM   #23
tsiros is offline tsiros  Greece
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and what happens when the capacitor fails? because they are known to do. and when they do, they short out.

maybe i sound paranoid, but the only thing i put is the iso standard mains plug with fusebox and switch. after that is the transformer.
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Old 12th March 2013, 11:13 AM   #24
DF96 is offline DF96  England
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X2 caps are designed to fail open circuit. In fact, that is one of their weaknesses as voltage spikes progressively erode the capacitor away so it reduces in value over a number of years.

Y caps are even safer - you are supposed to be able to trust a Y cap with your life!
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Old 12th March 2013, 11:40 AM   #25
AndrewT is offline AndrewT  Scotland
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.........maybe i sound paranoid, but the only thing i put is the iso standard mains plug with fusebox and switch. after that is the transformer.
You are potentially dangerously paranoid.
Understand the science before you play with mains electricity.
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Old 12th March 2013, 05:53 PM   #26
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May I add a word of warning, gleaned from personal experience, to anyone putting film caps (especially as large as 10uF) across the mains. They will hold their charge for an awfully long time because there is very little to dissipate it. And they can pack quite a punch when you finally put your fingers across the terminals. I doubt it would kill you unless you are wearing a pacemaker but you will be breathless and disoriented for a second.

Mine was a 400V 10uF Wima MKP10 that had been sitting on the bench for a few days after playing around just as you are discussing here. I would say that it's probably worse as a shock than your average touching the mains. FWIW I found nothing improved the sound and if anything made it worse. And that is consistent with my general experience and view on all things to do with mains conditioning or filtering, though I can't see anything against a common mode choke or keeping voltage spikes away from your electronics. Personally I would go to the items that are causing the mess, fridges etc., but even then I'm probably more interested in making my lightbulbs last longer than in cleaning up the mains.
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Old 12th March 2013, 06:45 PM   #27
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Cris: the solution is obvious: a 1 megaohm in parallel with the cap will discharge it in few seconds, and no risk is present.
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Old 13th March 2013, 01:20 PM   #28
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Cris: the solution is obvious: a 1 megaohm in parallel with the cap will discharge it in few seconds, and no risk is present.
Yes, Osvaldo, of course I'm aware of that now, , but 30 years of having capacitors littering your desk and never doing you any harm had led to me to an easy (and unjustified) complacency. Nor, even now, would I mentally judge that a capacitor of that size could hold enough charge to have more than a trivial physical effect. Sure, with 10,000V I would be careful, or with 10,000uF, but 10uF? If you get my drift, then you can see why it is an easy mistake to make. I just thought it might be worthwhile warning others about a not-that-obvious potential danger.
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Old 13th March 2013, 07:20 PM   #29
Mooly is offline Mooly  United Kingdom
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Originally Posted by Osvaldo de Banfield View Post
Cris: the solution is obvious: a 1 megaohm in parallel with the cap will discharge it in few seconds, and no risk is present.
And just to add that any resistor MUST be continuous "high voltage rated". Just calculating wattage is no good, resistors have voltage ratings and failure of ordinary resistors used like this is an industry wide problem.

I can tell you from experience that even a 0.1 uf charged to peak mains voltage (on 240 volts mains) can bite if you have damp hands. Many old TV's were like this and it was common for techs to get a belt off the mains plug of a disconnected appliance. One tech used to stand there swinging the mains lead smashing the plug tops off any that got him
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