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[#194] etsang3 - 大家齊來砌power supply #193 ... ＜＜"迴路"內有"電位差"也有"電阻"=我先估計大家的器材沒有漏電（有已處理了）所以他們"地"線之間沒有"電位差"，就算有"迴路"也沒有電流流動 ... etsang3兄，漏電其實係唔正常現象，不如先排除這點。但ground loop係最常見(這亦非只是我意見，你google下hum noise + ground loop，就知有幾咁普通)，safety ground咁鬼長，又露曬出嚟(得層膠)，你唔可以唔計有L，safety ground 係pick up 到(或有電流選擇行呢尐path!?)，唔係因為漏電，呢個就係#192嘅解釋！ ground loop還有帶出更多其它noise嘅問題！最後修改時間: 2015-05-28 11:19:13		edn 正式會員 58.xxx.xxx.243	2015-05-28 11:11

[#193] etsang3 - 大家齊來砌power supply
edn 兄,

我都同意以下幾點,但要注意它們是有"因"才有"果"。
沒有"因"但有"果",只去避開"果"則還不是處事的好方法。
通常我們看了有以下的原因,以為它們也"應該"出現在自己套HiFi,
自己對號入座。如主"因"捉不到,實是”事半工倍"的。
這是我對一般hum噪音的"因"的見解。大家研究同意否及
自己有多少可能有以下問題。

Hum noise 其中三個原因:
1) 漏電
／／這問題最常見。有或無，簡單用"他電筆"便能確定。
有一定要處理，人身安全很重要，因此問題聲音也不好。
漏電去了其他器材也影響它的工作。因為HiFi一般是”雙重絕緣”器材，內的火牛初次級做了市電隔離，"應該"不可能會漏電的，除非火牛壞了或絕緣能力衰老。
所以兩腳插蘇也安全的。兩腳插蘇器材通常"他電筆"也會有微光的，那不是真正漏電，是火牛初次級線圈的一點點電容偶合效應，一接地也不亮了。

2) Ground loop　（地迴路)
3) induction (電磁感應)
／／這問題要有以下種種的"因"才能出現問題，缺一不可。
要有接”地”及有"迴路"
(A機RCA地－＞A機電源地－＞B機電源地-＞B機RCA地)
及地"迴路"內有"電位差"也有"電阻", 所以產生迴路座噪音電流(50Hz, 100Hz）
或"迴路"感應了外面的電磁場（50Hz, 100Hz)

大家來看看你的組合和電源有無可能有這些"因"，有才要去擔心考慮。

＜＜接”地”及有"迴路"=只後級或前級有三腳插蘇接地，沒有迴路，沒有問題。
全部三腳插蘇有地有迴路（是說有20呎的電源＋訊號線的"迴路"），有可能有問題。往下看。

＜＜"迴路"內有"電位差"也有"電阻"=我先估計大家的器材沒有漏電（有已處理了）所以他們"地"線之間沒有"電位差"，就算有"迴路"也沒有電流流動
我估大家用比較粗的電源線，都插在一個比較好的拖板上，電源線的地線和拖板的地線電阻在1 ohm以下，可當成無電阻了，些少的"電位差"也會比帶去了電箱的地化解了。此”因”也很能成立。

＜＜"迴路"感應了外面的電磁場 = 要形成這個因比較困難。要感應外來電磁場而那力度能影響我們的小ground loop的．．．
a. 要一個大而恆定的磁場，例如有一個大漏磁的火牛（如CRT消磁線圈能力)
b. 小磁場但要一個很大的"迴路" (這大"迴路"一般不能在我們的家出現)
我們機內的火牛漏磁很小的，它的漏磁可以不考慮。

可以見到，處理好漏電，造好接地方法及地線品質，是最能治本的。

etsang3

正式會員
58.xxx.xxx.198

2015-05-28 09:44

[#192] etsang3 - 大家齊來砌power supply

http://www.soundonsound.com/sos/1994_articles/aug94/groundloops.html
...

THE GROUND LOOP

As mentioned earlier, a typical home studio includes numerous mains-powered pieces of equipment joined to each other via unbalanced screened cables. All the screens and mains earths interconnect, and because cable does have a finite resistance, there's a real danger that interference signals will cause current to flow in the cable screens, resulting in audible signal contamination. Most interfering signals, such as those from distant radio transmitters, are pretty feeble, but the 50Hz mains supply feeding your studio is a different matter. If you were to place a closed loop of wire inside a studio, you'd be able to measure a 50Hz current flowing in the wire, because the loop acts exactly like a transformer. Of course, real-life transformers have more than one turn of wire, but the principle is the same, and a very small percentage of the current flowing in the mains system gets inductively coupled into our wire loop. Because audio signals are measured in millivolts rather than volts, even the most inefficient coupling of the 240V mains supply into our wire loop will produce enough current to generate a voltage, which, when added to a typical audio signal, will be audible as hum.

...

edn

正式會員
58.xxx.xxx.141

2015-05-28 03:56

[#191] etsang3 - 大家齊來砌power supply
....

如果全部都無漏電,一機接地,或多部接地(仲好)都無問題。

...

少少意見:

safety ground 通常唔乾淨呵 (咁鬼長，又露曬出嚟(得層膠))！我覺得下面條link解釋得唔錯！(有尐日本機，唔接safety ground...) 就算乾淨，佢都依然係ground loop，...

Hum noise 其中三個原因:

1) 漏電

2) Ground loop (見以下解釋)

3) induction

...

http://ecmweb.com/content/finding-and-fixing-ground-loops-av-systems

...

How do I get rid of this noise? When a system contains two or more ground connections, whether through power cords to safety ground or other grounded signal cables such as the CATV connection shown in Fig. 3 at left, a ground loop is formed. This ground loop provides a complete circuit path for ground noise current.

...

最後修改時間: 2015-05-28 03:58:52

edn

正式會員
58.xxx.xxx.141

2015-05-28 03:48

[#190] etsang3 - 大家齊來砌power supply
唔該晒etsang3 Sir，好詳細，我會跟你教的方法試試

thanks！

mc2

正式會員
59.xxx.xxx.3

2015-05-28 01:41

[#189] etsang3 - 大家齊來砌power supply

https://www.youtube.com/watch?v=l4famaQmWnA

edn

正式會員
58.xxx.xxx.141

2015-05-28 00:30

[#188] etsang3 - 大家齊來砌power supply
http://en.wikipedia.org/wiki/Mains_hum

...
Causes of electric hum[edit]
Electric hum around transformers is caused by stray magnetic fields causing the enclosure and accessories to vibrate. Magnetostriction is a second source of vibration, where the core iron changes shape minutely when exposed to magnetic fields. The intensity of the fields, and thus the "hum" intensity, is a function of the applied voltage. Because the magnetic flux density is strongest twice every electrical cycle, the fundamental "hum" frequency will be twice the electrical frequency. Additional harmonics above 100 Hz or 120 Hz will be caused by the non-linear behavior of most common magnetic materials.
Around high-voltage power lines, hum may be produced by corona discharge.
In the realm of sound reinforcement (as in public address systems and loudspeakers), electric hum is often caused by induction. This hum is generated by oscillating electric currents induced in sensitive (high gain or high impedance) audio circuitry by the alternating electromagnetic fields emanating from nearby mains-powered devices like power transformers. The audible aspect of this sort of electric hum is produced by amplifiers and loudspeakers.
The other major source of hum in audio equipment is shared impedances; when a heavy current is flowing through a conductor (a ground trace) that a small-signal device is also connected to. All practical conductors will have a finite, if small, resistance, and the small resistance present means that devices using different points on the conductor as a ground reference will be at slightly different potentials. This hum is usually at the second harmonic of the power line frequency (100 Hz or 120 Hz), since the heavy ground currents are from AC to DC converters that rectify the mains waveform. See also ground loop.
In vacuum tube equipment, one potential source of hum is current leakage between the heaters and cathodes of the tubes. Another source is direct emission of electrons from the heater, or magnetic fields produced by the heater. Tubes for critical applications may have the heater circuit powered by direct current to prevent this source of hum.[1]
Prevention[edit]
It is often the case that electric hum at a venue is picked up via a ground loop. In this situation, an amplifier and a mixing desk are typically at some distance from one another. The chassis of each item is grounded via the mains earth pin, and is also connected along a different pathway via the conductor of a shielded cable. As these two pathways do not run alongside each other, an electrical circuit in the shape of a loop is formed. The same situation occurs between musical instrument amplifiers on stage and the mixing desk. To fix this, stage equipment often has a "ground lift" switch which breaks the loop. Another solution is to connect the source and destination through a 1:1 isolation transformer, called variously audio humbucker or iso coil. Another extremely dangerous option is to break contact with the ground wire by using an AC ground lift adapter or by breaking the earth pin off the power plug used at the mixing deck. Depending on the design and layout of the audio equipment, lethal voltages between the (now isolated) ground at the mixing desk and earth ground can then develop. Any contact between the AC line live terminals and the equipment chassis will energize all the cable shields and interconnected equipment.

...

edn

正式會員
58.xxx.xxx.141

2015-05-28 00:25

[#187] etsang3 - 大家齊來砌power supply
mc2兄,
我覺得有漏電情況出現在其中一部機或多部機漏。
如果全部都無漏電,一機接地,或多部接地(仲好)都無問題。
一般電源只兩腳無地線的機,漏電便會經RCA地走去其他機。
這些有漏電的機音源也帶多一點的hum干擾了。
最紮實的功夫都係消除漏電。
1. 先把"機去機"接線拆下, 使一部一部機成為孤島。
2. 用"他電筆"度機殼螺絲及RCA的"地"看看光亮度。
3. 有地線的機"他電筆"不應該亮燈。照樣亮燈要檢查地線通不通機殼
4. 用兩腳插蘇的機一般會微亮,反一反兩腳插蘇找出"他電筆"最暗的(或不亮),便是相位正確了。如"他電筆"頗亮的,及手背觸及機殼螺絲有比電的感覺,
試加一地線看看可否使"他電筆"不亮。如屋企馬上跳"水氣掣"則火牛及電源入力落地電容可能漏電了,要修理的。

把各機的漏電問題解決了,怎樣再接在一起也不再hum了。

最後修改時間: 2015-05-28 00:22:21

etsang3

正式會員
58.xxx.xxx.198

2015-05-28 00:14

[#186] etsang3 - 大家齊來砌power supply
謝謝Tsang sir解答,:)

linger

正式會員
222.xxx.xxx.202

2015-05-28 00:14

[#185] etsang3 - 大家齊來砌power supply
在power supply 中雙橋和單橋整流有什麼不同. ^-^ 哪個音效好D?
)))"雙橋"整流後(+) (-)才連出"地",(+)(-)供電互不干擾,條"地"穩定D,所以好聲D。

etsang3

正式會員
58.xxx.xxx.198

2015-05-27 23:40

[#184] etsang3 - 大家齊來砌power supply
etsang3 Sir
有些問題想請教，一般行RCA石擴音機，有些訊源會聽到電流聲，有些訊源就聽不到電流聲(背景好靜)，請問etsang3 Sir，多數問題是出在那部份呢？擴音機本身是無水線結構的，我試過在擴音機身殼螺
絲位加條獨立水線，水線另一邊接家裡的水線落地，有改善，電流聲細了，但仍然有。
發覺訊源當使用同軸結構訊號線(網做地兩邊接負極)，電流聲就無，可惜衰在音色不是我杯茶，反而好音色的單邊接地網VDH這類訊號線，電流聲明顯。
不過有1個訊源是接部獨立tuner，就算使用單邊接地網VDH這類訊號線，都無電流聲，超靜。
可解？
thanks！

最後修改時間: 2015-05-27 01:57:12

mc2

正式會員
59.xxx.xxx.3

2015-05-27 01:54

[#183] etsang3 - 大家齊來砌power supply
Tsang Sir 可唔可以講下, 在power supply 中雙橋和單橋整流有什麼不同. ^-^ 哪個音效好D?

linger

正式會員
222.xxx.xxx.202

2015-05-25 21:08

[#182] etsang3 - 大家齊來砌power supply
＞電容俠侶, 擺檔好多年了

嗰日幫襯時傾咗幾句，原來開咗三十幾年，仲多口話細路年代無留意佢哋，自然無幫襯過。用細小透明膠袋再用釘書機封口，乃鴨記街邊零件檔數十年如一日的習慣。

九斤老太

正式會員
219.xxx.xxx.27

2015-05-24 13:57

[#181] etsang3 - 大家齊來砌power supply
有兩粒在同一殼內慳位