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PostPosted: October 8th, 2020, 9:14 pm 
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Location: Baltimore MD
Just curious how often this could be a problem. There must be away to measure it.
Setting a multi meter to dc and trying to measure the mains dose not work.
Would the wave shape on a scope be distorted?


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PostPosted: October 8th, 2020, 9:29 pm 
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The power mains do not have a DC offset. Believe it or else.

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PostPosted: October 8th, 2020, 9:30 pm 
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The easiest way is to check the distortion of the AC waveform. The more asymmetrical the waveform is on an O'Scope, the more likely there is DC offset. If the o'scope can measure THD distortion on the input, that would give a measurement.

I had the problem here when the AC line at the power meter had dirty contacts. That was probably caused by a lightning strike in the area. The local power company came out and found it inspecting the power meter.

If you have access to a Fluke 43B power line analyzer, anything above 2% THD on the AC power line is where DC offset is suspect.


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PostPosted: October 8th, 2020, 9:39 pm 
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If you have a two channel scope that has math functions you can set one channel for DC measurement and the other for AC measurement and then use the subtraction function to determine the difference which is the DC component.


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PostPosted: October 9th, 2020, 6:46 am 
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Thanks guys
There are many circuit designs for DC blockers usually a diode bridge or two and some electrolytic caps.
It’s curious why so few manufacturers include them in their high end designs.
PS audio uses them in all power plants and their more expensive bits.
Thanks Tom for your input. I am planning on getting a digital scope soon that has math functions.
I am not sure that I have a real problem here or not.
I do have some buzzing once in awhile but it goes away fairly quickly.
Could this be another reason for our syste,s sounding different from time to time


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PostPosted: October 9th, 2020, 7:49 am 
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The buzzing is more likely to be caused by noise on the line than DC.

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PostPosted: October 9th, 2020, 9:11 am 
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Not seeing any noise on the scope


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PostPosted: October 9th, 2020, 9:39 am 
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What issue are you trying to resolve?

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PostPosted: October 9th, 2020, 10:50 am 
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mostly for educational benefits
also I have a friend that has buzz/hum in two plate amps for subs
he has PS Audio powerplants on everything else in his system


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PostPosted: October 9th, 2020, 12:39 pm 
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Pelliott321 wrote:
mostly for educational benefits
also I have a friend that has buzz/hum in two plate amps for subs
he has PS Audio powerplants on everything else in his system


Sounds like a ground loop....

Roscoe

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