Author Topic: DC offset in power line  (Read 1192 times)

WildRain

  • Freshman member
  • *
  • Posts: 36
    • View Profile
DC offset in power line
« on: September 28, 2017, 09:59:41 PM »
Any bro here has experience dealing with DC offset in the power line. My friend is struggling with this. His expensive Phono Pre and and Rega RP10 PSU both failed and the manufacturer points to potential DC offset.

Came across below old article when researching...however wanted to check here as well

https://pooraudiophile.com/2015/03/how-to-fix-dc-offset-and-transformer.html
Sony Z1es | Densen DM20 | DM30 | Dynaudio S1.4

Nordost Heimdall | Baldur | QED Genesis

Maestro | 7N-4030 | Plixir Elementa BAC3000 | PC

jb

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 301
    • View Profile
Re: DC offset in power line
« Reply #1 on: September 29, 2017, 12:50:12 PM »
Not sure about the DC offset on AC...but reading the measurement method is not correct information..as DC offset measured at amp speaker output is due to gain difference of the amp output transistors and usually have a voltage divider circuit to adjust till the DC offset to 0V..but as temperature drift sometime there may be small DC offset of 10 to 100mV but this will not kill your equipment. But I do notice our AC voltage can range from 215 to 248V depend on the time, and if the power supply circuit were not design properly, this may kill it.

WildRain

  • Freshman member
  • *
  • Posts: 36
    • View Profile
Re: DC offset in power line
« Reply #2 on: September 30, 2017, 11:15:54 AM »
DC offset measured at amp speaker output is due to gain difference of the amp output transistors and usually have a voltage divider circuit to adjust till the DC offset to 0V..but as temperature drift sometime there may be small DC offset of 10 to 100mV but this will not kill your equipment.

Thanks, although different topic, its interesting to know. Is there any easy way to findout/measure if your amp is affected by this? 
Sony Z1es | Densen DM20 | DM30 | Dynaudio S1.4

Nordost Heimdall | Baldur | QED Genesis

Maestro | 7N-4030 | Plixir Elementa BAC3000 | PC

jb

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 301
    • View Profile
Re: DC offset in power line
« Reply #3 on: October 01, 2017, 03:08:35 PM »
If you are talking about DC offset at amp spk output, yes you can measure it using multimeter set to DC range, what ever DC you measured is the DC offset.

But if you are talking about DC offset at AC supply, I don't think such issue exist in AC circuit. The article you attached is giving wrong information to sell the product.
Typical for AC supply, you will have phase lead or lag issue depend on whether you plug in a lot inductive circuit like big motor... that will change the power factor of AC power supply, so some audio product are actually capacitor that you plug into your receptor that will improve this condition.

WildRain

  • Freshman member
  • *
  • Posts: 36
    • View Profile
Re: DC offset in power line
« Reply #4 on: October 05, 2017, 12:21:35 AM »
But if you are talking about DC offset at AC supply, I don't think such issue exist in AC circuit. The article you attached is giving wrong information to sell the product.

My friend actually got the APC senior engineer to measure this using some special industrial equipment from Fluke Networks. However, the challenge is, the industrial equipment equipment is not easy to come by, and also not quite affordable.
Sony Z1es | Densen DM20 | DM30 | Dynaudio S1.4

Nordost Heimdall | Baldur | QED Genesis

Maestro | 7N-4030 | Plixir Elementa BAC3000 | PC

Wizardofoz

  • Global Moderator
  • Jr. Member
  • *****
  • Posts: 57
    • View Profile
Re: DC offset in power line
« Reply #5 on: October 05, 2017, 02:56:14 AM »
I seem to recall there is some easy way to kill such DC offsets with a bridge rectifier and some caps (I could be wrong tho)...they are also known to wreak havoc with toroidal transformers too I think.

jb

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 301
    • View Profile
Re: DC offset in power line
« Reply #6 on: October 05, 2017, 03:49:00 PM »
I think the closest to DC offset, is when u have switch big inductive device causing a few cycle of AC transient surge...see attach link... but most of time your AC distributor circuit breaker should be able to protect against such issue.

http://myelectrical.com/notes/entryid/134/dc-component-of-asymmetrical-faults

else if you are advantageous enough, there are few variation of circuit on DIY audio forum that you can try at your own risk!


http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html

jb

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 301
    • View Profile
Re: DC offset in power line
« Reply #7 on: October 09, 2017, 12:10:15 PM »
Found a more details analysis of this...the circuit is lump to an switch circuit with inductor and resistor in series as shown below:
From the final solved equation, the first term is the AC signal with a second term that generate DC signal depend on the condition...




WildRain

  • Freshman member
  • *
  • Posts: 36
    • View Profile
Re: DC offset in power line
« Reply #8 on: October 10, 2017, 10:43:31 AM »
Found a more details analysis of this...the circuit is lump to an switch circuit with inductor and resistor in series as shown below:
From the final solved equation, the first term is the AC signal with a second term that generate DC signal depend on the condition...




Woah bro!

reminds me of UG exam prep : )
Sony Z1es | Densen DM20 | DM30 | Dynaudio S1.4

Nordost Heimdall | Baldur | QED Genesis

Maestro | 7N-4030 | Plixir Elementa BAC3000 | PC

jb

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 301
    • View Profile
Re: DC offset in power line
« Reply #9 on: October 11, 2017, 05:09:14 PM »
yes, it proves at least the high level math has some useful to our daily staff...haha
This guy math skill is power! as he solved using linear differential equations method, then he used a second method using Laplace transform method to solve  and is very elegant. Good exercise for the brain..haha