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Old 7th August 2010, 11:09 AM   #1
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Default Hum through speakers using GC & Laptop

My Gainclone emits a humming noise at the speakers when I use my laptop connected to is switched mode PSU. It is fine on battery supply.

Could it be DC on the output of the laptop when the PSU is connected, or is it a grounding issue?

Anything I could try to eliminate the problem?

I don't want to modify the inputs on the Gainclone, but I could make up some modified cables (in-line caps) to use with the laptop.

Chris.
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Old 7th August 2010, 12:11 PM   #2
gfiandy is offline gfiandy  United Kingdom
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If it is humming then this is due to AC mains noise. So you probably have a ground loop.

Is your gain clones 0v connected to mains ground? If not try a 100R resistor from 0v on the gain clone to mains earth, this sometimes helps with this kind of noise. You can go lower if yuo want to right down to connecting 0v directly to mains earth.

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Andrew
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Old 7th August 2010, 01:50 PM   #3
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Definitely sounds like a grounding issue. What might be happening is RF hash from the mains coming down the screen of your audio cable into your gainclone. As Andrew says, earthing the 0v might reduce it considerably by providing a preferential path for the noise. If your input signal screen goes to the PCB then try connecting that to the chassis star point instead (assuming you have one).
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Old 7th August 2010, 11:07 PM   #4
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I don't think it is a ground loop issue with the gainclone. It is fine using my CDP and tuner as a source (through my passive attenuator)
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Old 7th August 2010, 11:49 PM   #5
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Do both your CDP and tuner have relatively dirty SMPSUs? They'll also generate far less digital hash than a laptop. Its grounding all right, but not a ground loop as such.
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Old 8th August 2010, 09:13 PM   #6
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Every time i've seen this happen it's caused by the power brick of the laptop. Confirm by running the laptop on battery - the hum should go away. Since a laptop doesn't pose an electric shock risk, most of the times the easiest solution is to cheat and plug the laptop in an ungrounded outlet.
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Old 8th August 2010, 10:33 PM   #7
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by Th3 uN1Qu3 View Post
Every time I've seen this happen it's caused by the power brick of the laptop. Confirm by running the laptop on battery - the hum should go away. Since a laptop doesn't pose an electric shock risk, most of the times the easiest solution is to cheat and plug the laptop in an ungrounded outlet.
you should not need to cheat.
The remote PSU for the Laptop is almost always double insulated and is fed from a two core cable, no earth wire.
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Old 9th August 2010, 12:45 PM   #8
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Quote:
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you should not need to cheat.
The remote PSU for the Laptop is almost always double insulated and is fed from a two core cable, no earth wire.
All the laptops i've had came with 3-wire cables on their power bricks. On one of them i actually fried the line input when connecting another piece of ungrounded equipment to it, because the laptop was plugged into a grounded outlet, and later i determined that the other equipment was sitting 55 volts above ground...
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Old 9th August 2010, 02:03 PM   #9
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Quote:
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you should not need to cheat.
The remote PSU for the Laptop is almost always double insulated and is fed from a two core cable, no earth wire.


In what country?

The company I work for is one of the largest resellers of computers/laptops in the world, and there has yet to be a laptop come through our evaluation dept that has a 2 prong plug, they ALL have ground pins.

we do 5 of EVERY HP,Dell,Lenovo/IBM,Toshiba,Panasonic model they make per year.


And they all have 3 pin plugs, that are electrically grounded to the power brick.
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Old 9th August 2010, 06:00 PM   #10
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It is a three pin PSU. So what can I do about the hum, aside from removing the ground (which I really don't want to do)?
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