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PostPosted: June 7th, 2018, 4:22 pm 
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OK. So here is the result of my test of the laptop power supply scope measurements of the ground pin to actual ground. There are three screen grabs with voltage and frequency measurements. The test was done as follows:

First the PS was plugged directly into the power strip and noise was noticed coming from the amplifier. Next a three pin to two pin adapter was used to lift the ground and also allow measurements at the ground pin. The scope probe was connected with the ground lead connected to the ground in one of the strip sockets and the probe tip connected to the ground output terminal on the 3 to 2 adapter. The scope was used in a single shot mode so that the trace could be loaded to a flash drive. Three measurements were taken as the noise was not constant and varied with time.

From the images, you can see there is a considerable noise with peak to peak levels reaching over 4 V and RMS values over 400 mv. There were also a wide range of frequencies with some of the highest peaks with a frequency of over 1 MHz. Nasty stuff. Once the cord is connected to the line ground some of this will be swamped out but apparently enough remains on the line considering normal line impedance to cause problems.

I connected the PS to an old Tenma 180 watt isolation transformer that has a completely isolated and faraday shielded secondary with a two prong socket and no ground connection on the secondary. The system was now dead quiet. I would feel fairly safe with this type of connection as the switchers are usually hi-pot tested for isolation with at least 2KV. Most isolation transformers also have at least the same voltage level for hi-pot testing. So I am more likely to win the lottery than to have both the PS and isolation transformer to break down at the same time. But, here comes the mandatory disclaimer. Multiple failures do happen so if you ever lift a ground connection do so at your own risk.

In addition to the screen grabs I am also including two links, one to a spec sheet on a Hammond 200 watt isolation transformer that should be more than sufficient for any reasonable laptop. The other is to Newark who will be happy to sell you one for only $91.74 on the web. The Hammond unit has a 3 wire receptacle on the secondary with the ground in use. You will have to use a ground lift plug to break the ground sneak path if you use this transformer. Remember it is being use only for safety.

http://www.hammondmfg.com/171.htm

http://www.newark.com/hammond/171b/tran ... dp/96F5545


Attachments:
Laptop PS ground noise 1.jpg
Laptop PS ground noise 1.jpg [ 227.8 KiB | Viewed 9711 times ]
Laptop PS ground noise 2.jpg
Laptop PS ground noise 2.jpg [ 207.76 KiB | Viewed 9711 times ]
Laptop PS ground noise 3.jpg
Laptop PS ground noise 3.jpg [ 225.46 KiB | Viewed 9711 times ]
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PostPosted: June 7th, 2018, 8:58 pm 
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Location: Baltimore MD
Transedent Sound has an balanced isolation xformers kit
https://www.transcendentsound.com/Transcendent_Sound_Power_Supply.html


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PostPosted: June 8th, 2018, 9:17 am 
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The key would be how it creates its derived ground. In any case if the noise is not coming in from the line that is a very expensive alternative. Remember, the isolation transformer is just an added layer of safety if you lift the ground which is the real problem solver.


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PostPosted: June 8th, 2018, 9:25 am 
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Tom,

What did this noise actually soundlike through your speakers? Was it continuous or sporadic?

tomp wrote:
OK. So here is the result of my test of the laptop power supply scope measurements of the ground pin to actual ground. There are three screen grabs with voltage and frequency measurements. The test was done as follows:

First the PS was plugged directly into the power strip and noise was noticed coming from the amplifier. Next a three pin to two pin adapter was used to lift the ground and also allow measurements at the ground pin. The scope probe was connected with the ground lead connected to the ground in one of the strip sockets and the probe tip connected to the ground output terminal on the 3 to 2 adapter. The scope was used in a single shot mode so that the trace could be loaded to a flash drive. Three measurements were taken as the noise was not constant and varied with time.

From the images, you can see there is a considerable noise with peak to peak levels reaching over 4 V and RMS values over 400 mv. There were also a wide range of frequencies with some of the highest peaks with a frequency of over 1 MHz. Nasty stuff. Once the cord is connected to the line ground some of this will be swamped out but apparently enough remains on the line considering normal line impedance to cause problems.

I connected the PS to an old Tenma 180 watt isolation transformer that has a completely isolated and faraday shielded secondary with a two prong socket and no ground connection on the secondary. The system was now dead quiet. I would feel fairly safe with this type of connection as the switchers are usually hi-pot tested for isolation with at least 2KV. Most isolation transformers also have at least the same voltage level for hi-pot testing. So I am more likely to win the lottery than to have both the PS and isolation transformer to break down at the same time. But, here comes the mandatory disclaimer. Multiple failures do happen so if you ever lift a ground connection do so at your own risk.

In addition to the screen grabs I am also including two links, one to a spec sheet on a Hammond 200 watt isolation transformer that should be more than sufficient for any reasonable laptop. The other is to Newark who will be happy to sell you one for only $91.74 on the web. The Hammond unit has a 3 wire receptacle on the secondary with the ground in use. You will have to use a ground lift plug to break the ground sneak path if you use this transformer. Remember it is being use only for safety.

http://www.hammondmfg.com/171.htm

http://www.newark.com/hammond/171b/tran ... dp/96F5545


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PostPosted: June 8th, 2018, 10:23 am 
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It sounded random and at times not very noticable but it never went away. If an application was loading or you moved across the screen witht he mouse it got louder. It seems like processor activity was a bigger cause than disk but I can't say that for sure.


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PostPosted: June 8th, 2018, 5:11 pm 
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Thanks for the info Tom and Stu.

I found no measurable voltage difference between N-H and G-H in any of my outlets so I am assuming I don’t have the grounding issues that Stu mentioned? But what I do have is noisy lines, even running dedicated 20A line for my amps and a dedicated 15A line for sources. In addition, I have an 1800W balanced power transformer on the 15A line and a 20A Brickwall panel mounted surge protector/conditioner on the 20A line. But I still wonder about ground line noise? Have to think about this but I wonder if my balanced power conditioner is acting as an isolation transformer, it just taps out the out two legs on the secondary right?


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PostPosted: June 9th, 2018, 7:53 am 
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I found that the voltage between neutral and ground varied over time. Sometimes zero


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PostPosted: June 9th, 2018, 9:05 am 
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A caveat about measuring noise is that if using a meter you have to make sure your meter has sufficient response to measure at some of the noise frequencies. I have one inexpensive DVM that runs out of steam on AC measurements at around 1 KHz. Another that is a more expensive bench model has response to around 500 KHz. Looking at the scope traces you can see that there are some HF components on the "ground" to ground signal.

Also remember that much of this will be swamped out by the ground but what gets you into trouble is the ground impedance. In your home, your ground system is a safety ground, not a signal ground. Even if the impedance is relatively high it will keep you from getting fried but won't cure all the noise problems. Electrical codes do not care about audiophiles other than to keep them alive and also to prevent fires. Since in an unbalanced piece of equipment at some point the signal ground is tied to chassis ground you then have a path for even small residual amounts of noise on the ground circuit to get into the audio chain where often it is then amplified to annoying levels.

As far as how some of the isolators and power conditioners out in the market place work, I don't have a clue. If you can get a schematic you would know right away. Again, the noise in my situation is not representative by any means of all the noise problems so the ground problem is most certainly different from other cases. Noise problems are some of the most difficult things to troubleshoot. The most valuable tool to fix them is perserverance.


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PostPosted: June 9th, 2018, 9:30 am 
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That's why a separate ground rod (at least 8 ft and a large gauge wire from just outside ones listening room to your system worked for me. Everything was better.


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PostPosted: June 9th, 2018, 9:38 am 
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Looking at schematics, I think I am not getting any real protection from ground issues from my balanced power transformer. It looks like incoming ground is tied to both the electrostatic shield between primary and secondaries and also tied to the secondary center tap. So noise on ground has a direct path through the center tap.


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