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| [#21] etsang3 DIY 銅腰帶屏蔽火牛漏磁 "There is an active form of shielding where fields of counter EMF (equal but opposite) are generated to cancel out the offending fields. A good and simple example of this is the AC power transformer, where a "shorted turn" is used to generate a nulling field. The shorted turn, is a seamless band of copper that wraps the transformer core in one direction. When cut by the rising and collapsing magnetic flux -- caused by the transformer action -- the shorted turn acts as a very low impedance, high current secondary winding, and generates a counter EMF, and because this winding is shorted, it generates a rising and collapsing magnetic field of opposite polarity thereby nulling the original stray magnetic flux. In some cases of severe common mode noise, the shield can be made to carry an equal but opposite noise current to counter the interfering noise. However, this is not for the faint-of-heart: any slight change of the mechanical or electrical parameters, and the cancelling noise becomes the noise noise!" 妘怮嶊G句咁講, 即係shield左都唔一定係好事! |
xyz_ps 正式會員203.xxx.xxx.108 |
2008-12-01 20:40 | |
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| [#22] etsang3 DIY 銅腰帶屏蔽火牛漏磁 "Shielding is mostly used to block electrostatic or "E" fields (Faraday shield). However, if ferrous metal (tempered Mu Metal works best for magnetic fields) is used, then both electrostatic and some level of magnetic shielding is accomplished." "However, this is not for the faint-of-heart: any slight change of the mechanical or electrical parameters, and the cancelling noise becomes the noise noise!" 妘怮嶊G句咁講, 即係shield左都唔一定係好事!" So, just make it simple. Use a metal casing to enclose the transformer la ..... |
kwok787 正式會員 221.xxx.xxx.47 |
2008-12-01 20:49 |
| [#23] etsang3 DIY 銅腰帶屏蔽火牛漏磁 Do not make a short-circuited completed turn when using this kind of shielding. |
2A3 正式會員 218.xxx.xxx.81 |
2008-12-01 21:11 |
| [#24] etsang3 DIY 銅腰帶屏蔽火牛漏磁 繞在鐵芯裡面的(如初次級)是"turn", 繞在鐵芯外面的(like the above did by etsang3) 是shield. Turn 有電感，短路=電流無限大=燒牛，shield 唔會有電感，短路當然唔會燒牛，否則世上的牛已燒了大半。 Btw, I think estang3 was just demonstrating how to shield a power transformer if it does not have one. If your power transformer already has a metal shield like the one used by estang3 above(before his operation), I don't think you should break the original shield and do what estang did above. |
thomasc2 正式會員 202.xxx.xxx.162 |
2008-12-02 11:44 |
| [#25] etsang3 DIY 銅腰帶屏蔽火牛漏磁 Sorry, please ignor this part: "Btw, I think estang3 was just demonstrating how to shield a power transformer if it does not have one. If your power transformer already has a metal shield like the one used by estang3 above(before his operation), I don't think you should break the original shield and do what estang did above."" 老花，竟然睇到個牛原本有 complete shielding. |
thomasc2 正式會員 202.xxx.xxx.162 |
2008-12-02 11:47 |
| [#26] etsang3 DIY 銅腰帶屏蔽火牛漏磁 有時真係咁就比坁惘 etsang3師傅就可以diy自已來出好野玩靚聲 我d初哥就見到頭都雲 |
hkmk 正式會員 58.xxx.xxx.152 |
2008-12-02 16:04 |
| [#27] etsang3 DIY 銅腰帶屏蔽火牛漏磁 初哥最好就乜都唔好攪，起碼都還有聲。 |
thomasc2 正式會員 202.xxx.xxx.161 |
2008-12-02 16:19 |
| [#28] etsang3 DIY 銅腰帶屏蔽火牛漏磁 同意同意, 吾係火足都有之 |
hkmk 正式會員 58.xxx.xxx.152 |
2008-12-02 21:18 |
| [#29] etsang3 DIY 銅腰帶屏蔽火牛漏磁 .  |
沙田超人 正式會員 221.xxx.xxx.67 |
2008-12-03 01:40 |
| [#30] etsang3 DIY 銅腰帶屏蔽火牛漏磁 .  |
JBL之達人 正式會員 221.xxx.xxx.67 |
2008-12-03 01:53 |
| [#31] etsang3 DIY 銅腰帶屏蔽火牛漏磁 onkyo 875  |
JBL之達人 正式會員 221.xxx.xxx.203 |
2008-12-03 02:33 |
| [#32] etsang3 DIY 銅腰帶屏蔽火牛漏磁 Balanced Line Isolation Transformer (Zero Impedance)  |
JBL之達人 正式會員 221.xxx.xxx.203 |
2008-12-03 02:42 |
| [#33] etsang3 DIY 銅腰帶屏蔽火牛漏磁 用銅片屏蔽是靠漏火牛產生的flux差令銅片通電，基本上是一個short turn。無漏磁的話，鐵心兩個方向的flux會底消，銅片無induced current。有漏磁的話中間鐵心的flux比外圍略大，所以便有induced current(Faraday's law)。如果漏磁嚴重，屏蔽銅片會熱到飛起。 環牛千萬不要用，因為用銅片順著線包環牛等於short turns，即刻燒。環牛安裝也要小心，例如中間鏍絲及鐵片也不能連到地，否則即燒。外圉包銅片一些作用也沒有，唯一有效方法是鐵殼，銅殼效果很低。不過好的環牛漏磁很小，如非Phono Amp，可以不理。 |
hetzer 正式會員 219.xxx.xxx.87 |
2008-12-03 19:26 |
| [#34] etsang3 DIY 銅腰帶屏蔽火牛漏磁 """環牛安裝也要小心，例如中間鏍絲及鐵片也不能連到地，否則即燒""" 如衹有一邊(如底部)連到，並不會構成closed loop，就唔會有事。地應該是指機殼。 |
thomasc2 正式會員 218.xxx.xxx.151 |
2008-12-03 21:20 |
| [#35] etsang3 DIY 銅腰帶屏蔽火牛漏磁 .. |
cubixx 正式會員 203.xxx.xxx.157 |
2010-02-16 20:18 |
| [#36] etsang3 DIY 銅腰帶屏蔽火牛漏磁 學習.學習............. |
camzan 正式會員 58.xxx.xxx.169 |
2010-02-17 19:36 |
