X2 Line capacitors

[argonrepublic]

Can I expect any immediate improvements using X2 capacitors across my AC line? It was reccommend to me. I thought it would be best to have this confirmed by members of this forum.
Thank you

[Mooly]

Audible improvements ? I would say probably no, but the feel good factor may make that a yes... if you see what I mean

[Osvaldo de Banfield]

X2 capacitors per se are of no utility.

X2 caps are such that are wired between two live poles in the input of the power supply, and Y are such that are wired between each pole and earth. Both are designed to aid in the line filtering both to difficult the input of interference signals from and into the equipment under question. But between them usually is placed a common mode inductor that consist of two winding in a ferrite core in the same direction, and as hardly coupled as consistent with isolation permits. Then, from line to rig, first it is placed the X2 cap (usually about 1µF 400V for 220V AC line), then the common mode choke (about 20mHy per side) and then the Y caps (.01µF 1KV). Then, X caps complete the cancelling in the line, and the Y caps derives interference to earth. The Y caps are a compromise, because a high value will give better filtering, but may trip the earth leakage device at home (Here known as "disyuntor"), and a too low value give no filtering. Sometimes, in SMPS's where also there is a PFC unit, two or three of them are cascaded to improve filtering noises.

[frank1]

Originally Posted by argonrepublic

Can I expect any immediate improvements using X2 capacitors across my AC line? It was reccommend to me. I thought it would be best to have this confirmed by members of this forum.
Thank you

Main filters are usually used to prevent noise escaping OUT of electronic equipment rather than noise getting IN as most electronic kit is relatively immune to this.
Frank

[DF96]

An X2 cap across the mains transformer primary can suppress arcing at the switch so lengthen its life and reduce switch-off noises. It will make very little difference to sound under normal operation.

[ClaveFremen]

Originally Posted by argonrepublic

Can I expect any immediate improvements using X2 capacitors across my AC line?

Often it will give an improvement, modest most of the times.

Originally Posted by DF96

An X2 cap across the mains transformer primary can suppress arcing at the switch so lengthen its life and reduce switch-off noises.

To achieve maximum results shouldn't the cap be as near as possible to switch pins?

[abraxalito]

Originally Posted by Osvaldo de Banfield

But between them usually is placed a common mode inductor that consist of two winding in a ferrite core in the same direction, and as hardly coupled as consistent with isolation permits.

X2 caps make very little or no difference by themselves, however when combined with a CM choke - especially one of segmented design for improved HF rejection - that's a very likely positive move in SQ.

[samoloko]

would you recommend a X2 value
I see different applications with a wide range from 0.0022 to 1 uF

[DF96]

Originally Posted by ClaveFremen

To achieve maximum results shouldn't the cap be as near as possible to switch pins?

No, this is not necessary. With the capacitor in place across the transformer primary the frequency components in the switch-off transient are much lower than they would be, so distance of connection does not matter.

Originally Posted by samoloko

I see different applications with a wide range from 0.0022 to 1 uF

That is because the exact value does not matter very much. Personally I would use somewhere between 5nF and 100nF. If you really want to you can calculate the value after measuring the transformer inductance and resistance, but few people bother.

[frank1]

Originally Posted by ClaveFremen

Often it will give an improvement, modest most of the times.

An improvement in what?
Unless it can remove something on the mains that the amp is overly sensitive to (doubtful if it could), then it will make absolutely no measurable difference.

Frank