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Old 01-07-2015, 08:05 PM
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tdelahanty tdelahanty is offline
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Default DC on AC line

This is a good question for Dan. I have 650mv dc on the AC line. I checked this because things just didn't sound right. Dan how much dc is acceptable ?
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Old 02-01-2015, 02:42 PM
Glisse Glisse is offline
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I use a Burmester 948 power conditioner, which removes DC on the line.

When I forget to engage the DC circuit in the 948, such as after a reboot of the system, it takes me about 30 seconds to realise something is wrong. I have around 250mV on the AC line. 650mV seems very high.
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Old 02-01-2015, 05:12 PM
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Quote:
Originally Posted by tdelahanty View Post
This is a good question for Dan. I have 650mv dc on the AC line. I checked this because things just didn't sound right. Dan how much dc is acceptable ?
Tom.......First, how are you coming up with the 650mv measurement? Are you measuring with a DMM or an oscilloscope? Which wires are you measuring, i.e. hot to neutral, hot to ground, or neutral to ground?

It is not unusual to have some level of DC offset on AC lines in your home. This is often caused by variable speed AC motors like those found on a hair dryer and by switch mode power supplies in electronics and computers that create DC by chopping half the AC sine wave to make a pulsing DC output. This causes the other half of the sine wave, also a pulsing DC, to be back fed onto the neutral which generates heat in the cores on transformers. Under perfect conditions the neutral tap on any transformer should have zero AC or DC when referenced to ground.

650 millivolts (0.65 VDC) is not a serious problem on a AC line but ideally zero DC would be the best. You can probably reduce the DC offset on your home power by turning off (unplugging) anything with a switch mode power supply when not in use.
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Last edited by jdandy; 02-01-2015 at 05:45 PM.
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Old 02-01-2015, 05:16 PM
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Quote:
Originally Posted by jdandy View Post
Tom.......First, how are you coming up with the 650mv measurement? Are you measuring with a DMM or an oscilloscope? Which wires are you measuring, i.e. hot to neutral, hot to ground, or neutral to ground?

It is not unusual to have some level of DC offset on AC lines in your home. This is often caused by variable speed AC motors like those found on a hair dryer and by switch mode power supplies in electronics and computers that create DC by chopping half the AC sine wave to make a pulsing DC output. This causes the other half of the sine wave, also a pulsing DC, to be back fed onto the neutral which generates heat in the cores on transformers. Under perfect conditions the neutral tap on any transformer should have zero AC or DC when referenced to ground.

650 millivolts (0.65 VDC) is not a serious problem on a AC line but ideally zero DC would be the best. You can probably reduce the DC offset on your home power by turning off (unplugging) anything with a switch mode power supply when not in use.
Dan, I thought the issue was coming from switching power supplies and linear PSU was the way to go.

Last edited by jdandy; 02-01-2015 at 05:46 PM. Reason: Correct error in quote
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Old 02-01-2015, 05:22 PM
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Quote:
Originally Posted by antipop View Post
Dan, I thought the issue was coming from switching power supplies and linear PSU was the way to go.
Georges.......Not all linear power supplies are created equal but you are correct that the largest contributors to DC offset on AC power lines are switch mode power supplies.

It is easy to overlook just how many switch mode power supplies are in the typical home. Nearly all wall wart charges that make DC for cellphones, calculators, laptop computers, tablet computers, iPods, rechargeable flashlight batteries, security cameras, LCD displays, desktop computer speakers, routers, and other devices can all contribute to the DC offset issue on a home's AC lines, not to mention switch mode power supplies in desktop computers and power bricks that produce DC power for audio devices.
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STUDIO - McIntosh C1000C/P, MC2301 (2), MR88, Aurender N10, Esoteric K-01X, Shunyata Sigma spdif digital cable, Sonos Connect, PurePower 2000, Stillpoints, Furutech Flux 50, Michell Gyro SE, Michell HR Power Supply, SME 309, Ortofon Cadenza Black, Wireworld, Sonus faber Amati Anniversario
LIVING ROOM - McIntosh C2300, MC75 (2), MR85, Magnum Dynalab 205, Simaudio MOON Neo 260D-T, Schiit Audio Yggdrasil, Aurender N100H, Shunyata Sigma USB cable, Micro Seiki DD40, Ortofon Cadenza Blue, Nakamichi BX-300, Sony 60ES DAT, PS Audio P10, Furutech Flux 50, Sonos Connect, Stillpoints, Wireworld, Kimber, PMC EB1i, JL Audio f113
VINTAGE - McIntosh MA230, Tandberg 3011A tuner, Olive 04HD, Sony DTC-59ES DAT, McIntosh 4300V, JBL 4312A

Last edited by jdandy; 02-01-2015 at 05:54 PM.
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  #6  
Old 02-02-2015, 06:03 AM
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tdelahanty tdelahanty is offline
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Quote:
Originally Posted by jdandy View Post
Tom.......First, how are you coming up with the 650mv measurement? Are you measuring with a DMM or an oscilloscope? Which wires are you measuring, i.e. hot to neutral, hot to ground, or neutral to ground?

It is not unusual to have some level of DC offset on AC lines in your home. This is often caused by variable speed AC motors like those found on a hair dryer and by switch mode power supplies in electronics and computers that create DC by chopping half the AC sine wave to make a pulsing DC output. This causes the other half of the sine wave, also a pulsing DC, to be back fed onto the neutral which generates heat in the cores on transformers. Under perfect conditions the neutral tap on any transformer should have zero AC or DC when referenced to ground.

650 millivolts (0.65 VDC) is not a serious problem on a AC line but ideally zero DC would be the best. You can probably reduce the DC offset on your home power by turning off (unplugging) anything with a switch mode power supply when not in use.
Dan I'm using a Fluke Model 87 (true rms) DVM and measuring hot to neutral. My audio line is direct to the box with nothing else on the circuit. However there are several devices in the house which have switching power supplies.
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