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Old 1st November 2009, 11:15 PM   #1
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Default Problem with isolated and lifted grounds

My NAD542 DVD player has no earth connection, like most other CD and DVD players. It has an insulated transformer and the earth pin from the power socket is not connected. It worked fine with my previous preamp and power amp without ground lift.

When I introduced ground lift (10R || 0.1uF with a 35A diode bridge connected to earth) to my preamp and power amp the Marantz SA11 SACD player, which also has no earth connection, worked fine.

But when I connected my DVD player to one of the preamp inputs, it was like adding an antenna to the input, even though that input was not selected. The hum was loud. During experiments, when plugging in the DVD player while the preamp was on, a loud bang was followed by the burning of the power amp fuse.

A DMM reading of the DVD playerís RCA ground and the power amp earth showed about 33mV.

Before introducing the ground lifts to the preamp and power amp, the DVD player worked fine, but then the overall hum level of the entire system was a bit higher.

I am now thinking about removing the ground lifts from the preamp and power amp!

The trouble is that I do not know exactly if lifting the grounds helps with reducing the hum or not. When I introduced the ground lifts, I also did much improved grounding and other stuff at the same time. The result was reduced hum and better sound. Was it because the ground lifts or other improvements? I donít know.

How can I solve this problem?
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Old 1st November 2009, 11:37 PM   #2
Bonsai is offline Bonsai  Taiwan
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Try not to fiddle with commercial consumer products. Usually, in terms of grounding and EMI, they are well engineered. They have tto be to get through safety and EMI/EMC standards.

Best advice: Return your euqipment to its original state.
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Old 1st November 2009, 11:55 PM   #3
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The preamp and power amps are not commercial products but DIY's. I have not changed the grounding of the CD player or the DVD player.
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Old 2nd November 2009, 12:03 AM   #4
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I would remove it from the preamp and leave it on the power amp.
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Old 2nd November 2009, 12:04 AM   #5
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Is this all connected to a television set with a rooftop antenna?
Try unplug the TV antenna & see if the hum goes away. Maybe a problem caused by the antenna's lightning ground.
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Old 2nd November 2009, 01:34 AM   #6
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Quote:
Originally Posted by MJL21193 View Post
I would remove it from the preamp and leave it on the power amp.
Yes, an option to be experimented.
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Old 2nd November 2009, 01:42 AM   #7
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Quote:
Originally Posted by Steerpike View Post
Is this all connected to a television set with a rooftop antenna?
Try unplug the TV antenna & see if the hum goes away. Maybe a problem caused by the antenna's lightning ground.
The DVD video is connected to a TV via a S-video cable. The TV is a large rear projection TV but I don't think (not sure though) it is earthed. The TV connects to a digital set-top box, not an outdoor antenna direct.

Thanks for pointing this out. At least now I know that I effectively connect the ground of the TV and the DVD player to the preamp.
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Old 2nd November 2009, 09:06 AM   #8
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Why was there a measured almost constant 35mV across the RCA shield ground of the DVD player and earth?
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Old 2nd November 2009, 09:15 AM   #9
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Default I have made an aerial, an antena, to a Citizen Band operator

If someone alike that guy, that wants to talk and wants to bother... lives nearby you..no grounding can protect you... no lifted ground will resist.

The guy wanted to disturb his surroundings...and no one, 500 meters around, can watch TV...also audio amplifiers are beeing interfered too.

The guy is crazy!... at least, his is bothering his own family, as the surroundings have only uncle...well...only family.

Carlos
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Last edited by destroyer X; 2nd November 2009 at 09:17 AM.
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Old 2nd November 2009, 11:41 AM   #10
rabbitz is offline rabbitz  Australia
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Try disconnecting (audio and video) from the TV and the DVD player and see if the noise is still there. I've had two issues in audio equipment that came back to the TV..... even in a different room and was coming via a FM tuner antenna cable that was common to both systems. The TV antenna has it's own cable.
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