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Grounding issues..... :(
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<blockquote data-quote="thylantyr" data-source="post: 2225115" data-attributes="member: 560358"><p>Here is the wiring for a common piece of electronics.</p><p></p><p><a href="http://sound.westhost.com/psw-f2.png" target="_blank">http://sound.westhost.com/psw-f2.png</a></p><p></p><p>IEC mains socket, node 'E' is earth ground. The 3rd prong on AC home voltage.</p><p></p><p>Notice the socket is node 'E' is connected to the metal chassis.</p><p></p><p>Same thing in schematic form.</p><p></p><p><a href="http://sound.westhost.com/psw-f1.png" target="_blank">http://sound.westhost.com/psw-f1.png</a></p><p></p><p>Notice they imply that center tapped T1 is grounded, the same ground as</p><p></p><p>AC input ground. This can create a ground loop as T1 output ground is also</p><p></p><p>connected to your AC mains all the time. If you disconnect the T1 ground</p><p></p><p>from chassis ground, you should have no issues, but if there is an electrical</p><p></p><p>'hot' short to chassis, there is no short circuit to protect the user from shock.</p><p></p><p>A clever approach to solve both issues, ground isolation and have protection is this.</p><p></p><p><a href="http://sound.westhost.com/p27-f3.gif" target="_blank">http://sound.westhost.com/p27-f3.gif</a></p><p></p><p>You install a bridge rectifier, one resistor, one cap. One side is earth/chassis connected, the other side goes to the electronics power supply ground.</p><p></p><p>Simplified, it looks like this;</p><p></p><p><a href="http://sound.westhost.com/p04_fig1.gif" target="_blank">http://sound.westhost.com/p04_fig1.gif</a></p><p></p><p>Two diodes.</p><p></p><p>The reason the bridge rectifier is used is because;</p><p></p><p>1. It's common and cheap, and easy to install.</p><p></p><p>Here's a beefy one;</p><p></p><p><a href="http://www.herbach.com/Merchant2/graphics/00000001/g4-015.jpg" target="_blank">http://www.herbach.com/Merchant2/graphics/00000001/g4-015.jpg</a></p><p></p><p>Medium sized;</p><p></p><p><a href="http://www.herbach.com/Merchant2/graphics/00000001/g4-004.jpg" target="_blank">http://www.herbach.com/Merchant2/graphics/00000001/g4-004.jpg</a></p><p></p><p>They come in different voltage and current ratings. To protect against short</p><p></p><p>circuit, the rectifier or diodes will need to have a high current rating so</p><p></p><p>when a short circuit happens, this gives the breaker or fuse time enough</p><p></p><p>to trip or blow, but you don't want your diodes to blow prematurely, hence</p><p></p><p>use high current diodes, maybe 30A rated.</p><p></p><p>I'm not sure if the resistor is really needed as it makes a low impedance path</p><p></p><p>from electronic ground.</p><p></p><p>How this works? referencing this pic;</p><p></p><p><a href="http://sound.westhost.com/p04_fig1.gif" target="_blank">http://sound.westhost.com/p04_fig1.gif</a></p><p></p><p>If the power supply high voltage touches the chassis, current passes through</p><p></p><p>D1 to it's ground return path, thus creating a short circuit and blowing the</p><p></p><p>5A fuse.</p><p></p><p>If there is no fault, the only path from electronics ground to earth {chassis ground} is through the 10 ohm resistor, essentially isolation both from</p><p></p><p>each other, albiet 10 ohms isn't much isolation, but if you have hum issues</p><p></p><p>still using this method, then I'd remove the resistor entirely and try it without.</p></blockquote><p></p>
[QUOTE="thylantyr, post: 2225115, member: 560358"] Here is the wiring for a common piece of electronics. [URL="http://sound.westhost.com/psw-f2.png"]http://sound.westhost.com/psw-f2.png[/URL] IEC mains socket, node 'E' is earth ground. The 3rd prong on AC home voltage. Notice the socket is node 'E' is connected to the metal chassis. Same thing in schematic form. [URL="http://sound.westhost.com/psw-f1.png"]http://sound.westhost.com/psw-f1.png[/URL] Notice they imply that center tapped T1 is grounded, the same ground as AC input ground. This can create a ground loop as T1 output ground is also connected to your AC mains all the time. If you disconnect the T1 ground from chassis ground, you should have no issues, but if there is an electrical 'hot' short to chassis, there is no short circuit to protect the user from shock. A clever approach to solve both issues, ground isolation and have protection is this. [URL="http://sound.westhost.com/p27-f3.gif"]http://sound.westhost.com/p27-f3.gif[/URL] You install a bridge rectifier, one resistor, one cap. One side is earth/chassis connected, the other side goes to the electronics power supply ground. Simplified, it looks like this; [URL="http://sound.westhost.com/p04_fig1.gif"]http://sound.westhost.com/p04_fig1.gif[/URL] Two diodes. The reason the bridge rectifier is used is because; 1. It's common and cheap, and easy to install. Here's a beefy one; [URL="http://www.herbach.com/Merchant2/graphics/00000001/g4-015.jpg"]http://www.herbach.com/Merchant2/graphics/00000001/g4-015.jpg[/URL] Medium sized; [URL="http://www.herbach.com/Merchant2/graphics/00000001/g4-004.jpg"]http://www.herbach.com/Merchant2/graphics/00000001/g4-004.jpg[/URL] They come in different voltage and current ratings. To protect against short circuit, the rectifier or diodes will need to have a high current rating so when a short circuit happens, this gives the breaker or fuse time enough to trip or blow, but you don't want your diodes to blow prematurely, hence use high current diodes, maybe 30A rated. I'm not sure if the resistor is really needed as it makes a low impedance path from electronic ground. How this works? referencing this pic; [URL="http://sound.westhost.com/p04_fig1.gif"]http://sound.westhost.com/p04_fig1.gif[/URL] If the power supply high voltage touches the chassis, current passes through D1 to it's ground return path, thus creating a short circuit and blowing the 5A fuse. If there is no fault, the only path from electronics ground to earth {chassis ground} is through the 10 ohm resistor, essentially isolation both from each other, albiet 10 ohms isn't much isolation, but if you have hum issues still using this method, then I'd remove the resistor entirely and try it without. [/QUOTE]
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