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Noise when on an amp

I get some electrical noise when I hookup my 1150 to my amp.  The amp is a fisher tube powered amp (very old).  It doesn't have any problems with all the other modern digital sources, just the 1150.

I can actually hear, for example, the CPU "think" through the speakers, and even the hard drives voice coil.  It's highly annoying.

I used shielded cables and even tried a 1:1 transformer.  Any other ideas?

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8 Krypton

Re: Noise when on an amp

 

Some of the Dell notebook computers can experience a Ground Loop noise under certain circumstances. This is mainly an issue on the older models.

Symptoms Include:
1.  A scratchy, staticy noise when moving the cursor, and
2. The noises occur only when the computer is plugged into its power adapter and not running on battery power, and
3. The noises occur only when the computer's output jack is connected to another device (like a mixer, power amp, etc) that is also plugged into a/c current with a grounded plug (3 prongs).

If you have similar noises but under different circumstances then it is not this Ground Loop noise.


To Diagnose:

1. Disconnect the power cord from the computer and run on battery power, or

2. Eliminate the ground either on the computer or on the other device it is connected to, by using a 3 prong to 2 prong adapter available at hardware stores. Use this adapter just as a temporary diagnostic tool because eliminating the ground can be potentially dangerous and could cause your warranty to become invalid.

In either case if the noise stops then it is the Ground Loop. It is caused by the design of the notebook's power adapter and there is no repair or replacement that can fix it, but there are some workaround solutions.


Solutions:

1. Isolate the grounds from each other by using a ground isolator. Several forum members have given us positive reports on Radio Shack's $16 Ground Loop Isolator (270-054). There are other such devices available for more money which would probably be better for someone doing pro audio work.

2. Or use non-conducting material to connect the 2 devices; specifically by using optical spdif (Toslink) to transfer the audio signal rather than copper cables. This is not as practical as the 1st solution because the notebook computers don't have an optical spdif port, so this would require getting an external soundcard that has optical spdif output, and a receiving device that has an optical spdif input port.

An external sound card is not in itself a solution, because you will still get the Ground Loop if you use its regular metal jacks to make connections, if the other circumstances described under 'Symptoms' are also present.

 

Jim Coates -- 15 years on the Dell Laptop Audio boards -- since 2/6/04 

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