Bizarre trouble...

arold19 · 11th March 2004, 01:59 AM

Hello, I have a bizarre trouble...
I have a gainclone at home and it work very well on my speaker at home. This week, I tried my gainclone with my friend system and it make a loud hum.....
I don't undertand, maybe because de "cheap" dvd player of my frind doesn't have ground ??
Maybe the speakers are two sentisive ???

With nothing at the input, it make no noise, when I plug the dvd player, the noise apper.

Do you know the problem ??

GregGC · 11th March 2004, 01:54 PM

Connect the two (amp and DVD) in the same power outlet and see if the hum still there. Something to do with the GND loops.
Is the DVD connected to a TV? Where is the TV connected to? Disconnect the TV from the DVD player.

/Greg.

arold19 · 11th March 2004, 04:43 PM

Yes, the video output of the DVD player is in the TV, and the audio output is in the gainclone.
This can cause a problem ???

arold19 · 11th March 2004, 10:47 PM

This was the problem! The noise leave when I disconnect the video cable.

But, How I can listen a movie??? If a plug the video cable, I have a big hum in the speakers and if I don'T plug the video cable, I don'T have image !!!!!!

The TV doesn't have any gound. The power cord of the TV have only 2 pin.

How can I repear this problem ???

Thank you !!!

dalbjerg · 12th March 2004, 01:16 AM

The TV doesn't have any gound. The power cord of the TV have only 2 pin
That's right but the TV is grounded thru the antenna cable. You can by an isolation trafo to either the antenna cable ore the audio (2)

leadbelly · 12th March 2004, 02:31 AM

If you do a search on "ground loop" you will come across many suggestions and examples of fixes. You will possibly need to buy or make yourself an isolation transformer for the cable connection.

AC devices are grounded even through a 2 pin plug. That's why it's important to not mix white wires and black wires.

leadbelly · 12th March 2004, 02:14 PM

Quote:

Originally posted by dalbjerg
[BThat's right but the TV is grounded thru the antenna cable. [/B]

No, that's misleading. The TV is grounded through the 2 pin plug AND the video cable. If it wasn't, there would be no loop. It's why the white wire is white and the black wire is black (or blue and brown overseas).

Frank Berry · 12th March 2004, 02:57 PM

Disconnect the TV antenna. Does the hum go away?

I have been able to break the ground loop in cases such as this by opening the shield of the TV antenna cable and connecting a couple of 100 pf capacitors across the break. This breaks the loop at audio frequencies but permits RF to pass.

dalbjerg · 13th March 2004, 01:14 AM

The TV is grounded through the 2 pin plug
I’m sorry too tell you that in the whole EU no TV is connected galvanic to ground thru the 2 AC wires. That will mean that you could have 230Vac (110V ) on the chassis. That would mean that you would actually touch the Powerline on the antenna plug, scart and SVHS if you turn your power plug the “wrong” way. The only connection to the Powerline came from the condensators in the net filter. In EU the CE marking tell that the only wire that most be grounded should be marked yellow/green, and must not draw any current <10mA.

leadbelly · 13th March 2004, 02:50 AM

Thanks for clearing that up. I had been under the impression that Europe had adopted polarized plugs as North America has.

11th March 2004, 01:59 AM	#1
arold19 diyAudio Member Join Date: Nov 2002 Location: montreal	Bizarre trouble... Hello, I have a bizarre trouble... I have a gainclone at home and it work very well on my speaker at home. This week, I tried my gainclone with my friend system and it make a loud hum..... I don't undertand, maybe because de "cheap" dvd player of my frind doesn't have ground ?? Maybe the speakers are two sentisive ??? With nothing at the input, it make no noise, when I plug the dvd player, the noise apper. Do you know the problem ??

12th March 2004, 02:31 AM	#6
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	If you do a search on "ground loop" you will come across many suggestions and examples of fixes. You will possibly need to buy or make yourself an isolation transformer for the cable connection. AC devices are grounded even through a 2 pin plug. That's why it's important to not mix white wires and black wires. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

12th March 2004, 02:57 PM	#8
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	Disconnect the TV antenna. Does the hum go away? I have been able to break the ground loop in cases such as this by opening the shield of the TV antenna cable and connecting a couple of 100 pf capacitors across the break. This breaks the loop at audio frequencies but permits RF to pass. __________________ Frank

13th March 2004, 02:50 AM	#10
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Thanks for clearing that up. I had been under the impression that Europe had adopted polarized plugs as North America has. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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11th March 2004, 01:54 PM	#2
GregGC diyAudio Member Join Date: Oct 2003 Location: Toronto	Connect the two (amp and DVD) in the same power outlet and see if the hum still there. Something to do with the GND loops. Is the DVD connected to a TV? Where is the TV connected to? Disconnect the TV from the DVD player. /Greg.

11th March 2004, 04:43 PM	#3
arold19 diyAudio Member Join Date: Nov 2002 Location: montreal	Yes, the video output of the DVD player is in the TV, and the audio output is in the gainclone. This can cause a problem ???

11th March 2004, 10:47 PM	#4
arold19 diyAudio Member Join Date: Nov 2002 Location: montreal	This was the problem! The noise leave when I disconnect the video cable. But, How I can listen a movie??? If a plug the video cable, I have a big hum in the speakers and if I don'T plug the video cable, I don'T have image !!!!!! The TV doesn't have any gound. The power cord of the TV have only 2 pin. How can I repear this problem ??? Thank you !!!

12th March 2004, 01:16 AM	#5
dalbjerg diyAudio Member Join Date: Jul 2003 Location: Denmark	The TV doesn't have any gound. The power cord of the TV have only 2 pin That's right but the TV is grounded thru the antenna cable. You can by an isolation trafo to either the antenna cable ore the audio (2)

13th March 2004, 01:14 AM	#9
dalbjerg diyAudio Member Join Date: Jul 2003 Location: Denmark	The TV is grounded through the 2 pin plug I’m sorry too tell you that in the whole EU no TV is connected galvanic to ground thru the 2 AC wires. That will mean that you could have 230Vac (110V ) on the chassis. That would mean that you would actually touch the Powerline on the antenna plug, scart and SVHS if you turn your power plug the “wrong” way. The only connection to the Powerline came from the condensators in the net filter. In EU the CE marking tell that the only wire that most be grounded should be marked yellow/green, and must not draw any current <10mA.

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