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Old 8th June 2010, 12:15 PM   #1
sacpul is offline sacpul  Malta
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Default Earth Not Connected

I have these 2 valve items and my father with 45years experience working on valve amplifiers has found that these 2 items where not earth connected. The chasey as not connected to the earth. "Xiang Sheng 728A" "MENG Series X1 6P1"

From the circuit diagram there is a particular common earth, but when you check them by a multimeter to earth of the ac mains plug it is not connected. He has conected them to earth and the sound quality has been improved and also another little bit of the outut on the speakers.

Why these are not connected from the factory standard?
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Old 8th June 2010, 12:43 PM   #2
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Location: Cascais
Because too many customers had problems with ground loops?
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Old 8th June 2010, 12:44 PM   #3
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Hi there,

Can you post the schematic, and show which connection was missing?
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Old 8th June 2010, 02:28 PM   #4
sacpul is offline sacpul  Malta
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Join Date: Jul 2009
For safety requirements the earth need to be connected as the chasey is made of metal or aluminium.

There is the high voltage. Imgaine by a fault that the high voltage will be with chasey. What would happened to you?

There is a circuit on this forum of the amplifier. The earth is connected on the circuit diagram but when I open the amplifier, the earth conncection via the ac mains plug was not connected. I have done it with the help of my father.

For myself doesn't make sense that earth is not connected. There should be a switch like the guitar amplifiers to be earth isolated.
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Old 8th June 2010, 10:16 PM   #5
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Location: Cape Cod
You are correct that the chassis should always be grounded. I would suggest that there should not be a switch to disconnect chassis ground.

These are very inexpensive consumer electronic gear and there have been numerous instances on several forums about shoddy construction and incorrect wiring. I would avoid all of those Chinese amps.
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Old 9th June 2010, 10:23 AM   #6
Ian444 is offline Ian444  Australia
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Join Date: Nov 2008
Location: Brisbane QLD
Yes, on the Meng 6P1 series amps there is no wire from the IEC mains socket earth to the chassis. It has nothing to do with hum, they just leave it unconnected. It is the difference between cultures and safety standards or implementation/enforcement of safety standards as far as I can see. With the internet opening up massive international consumer sales, consumers need to be careful about what they buy, since overseas equipment may not meet local manufacturing safety standards. Buyer beware. For many DIY'ers, the cheaper Chinese amps are great to learn about tubes and experiment with, due to the very low price.

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Old 9th June 2010, 12:07 PM   #7
sacpul is offline sacpul  Malta
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Join Date: Jul 2009
Compare the value of the product to the money spend on it and then do this small modification on it is worth it.

But for those people who doesn't know with this earth or ground connection they will be in trouble. I will advise my friends that have valve amplifiers to check about this small connection
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Old 30th March 2013, 01:46 AM   #8
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Got pictures on the mod? I'm a new to DIY but figure I might be able to do this. planning on getting the 728A soon.
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