請教各位前輩，小弟近期購入Marantz sr5011環繞擴大機，
電源線不是3pin的，是傳統2pin的，
擴大機插座也只有2pin，是不是就沒有接地線？
小弟日後要買電源線，是不是也要買2pin的？
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1. 3 prong (不是pin)的電源主要是加強安全,也就是萬一有外來的電干擾, 如靜電,打雷等發生時,能夠更有效的從第三個(中間的)prong給通地導掉.
2. 一般而言,現在家裡的總電源保險絲盒裏通常已經做了充分的接地線,所以如果家裡的電器有些雖然只有2 prong,但也能由總電源那邊給予有效的接地保護.
3. 如果訊號互相連接在一起的器材(如擴大機接很多器材,甚至也接cable TV)都有3 prong接地線的話,就很容易產生共地迴路(ground loop),然後就會產生電器的哼聲. XLR接頭可以有效排除哼聲,光纖基本上對哼聲也是免疫, 但RCA接頭,HDMI和同軸線則非常容易受到迴路哼聲的影響.
4. 因此,大部分擴大機都做2 prong,但內部的隔離做得很好,一方面減少哼聲的產生,一方面其實也保護電干擾的危險.
5. 你如果買個3 prong的電源線接上去, 雖然是可以,但事實上也沒用. 因為接上去SR5011這邊只有2 prong,雖然接上去了,但第3 prong並沒有接觸到.
6. 你如果真正不放心外在電的危險干擾,一定要接地線,那就接在擴大機的外殼,而不要讓地線跟擴大機本身電路有任何的瓜葛,以免產生共地迴路.
請參考:
http://subig1957.pixnet.net/blog/post/17150941-%E6%8E%A5%E5%9C%B0%CB%99%E6%84%9F%E6%87%89%CB%99%E9%9A%94%E9%9B%A2%E8%88%87%E4%BA%A4%E6%B5%81%E8%81%B2%E7%9A%84%E8%A3%9C%E8%BF%B0(%E4%B8%80)
http://www.avsforum.com/forum/90-receivers-amps-processors/1429874-why-only-2-prong.html
A 3-prong setup is prone to ground loops if the system includes other 3-prong equipment or cable/satellite TV. For example: If the preamplifier uses three prongs it is grounded not only through its power cord but also through any non-optical connections to other 3-prong components. This can result in humming or buzzing through the speakers as well as video problems. The more elaborate the system, the greater the chance of a ground loop. With 3-prong equipment, balanced XLR interconnection is needed throughout and that's not always available.
With 2-prong done right, safety is maintained through double or reinforced insulation. The next time you see a corded power tool, look for the double-square symbol - it represents this type of insulation. It requires more expensive wiring on the live side, and greater distance between live circuits and isolated circuits, and chassis. The distance requirement also applies to spacing inside transformers, making them larger and more expensive. A 2-prong cord also requires a larger line filter because according to safety standards the line-chassis leakage current limit is ten times lower compared to 3-prong. Ironically, the higher leakage current allowance in 3-prong systems aggravates hum problems in them!
To clear up other misconceptions, the earth ground provided by the third prong is not meant as a shield, it is a safety measure meant to trip breakers should a chassis become live as a result of a live wire contacting and shorting into it.
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