DIY Main DC Blocker

[Tam Nguyen]

The power at my area has DC offset so the need to block DC offset is high.

Some solutions available for 240V of Australia such as http://www.6moons.com/audioreviews/vibex/2.html ; http://www.kempelektroniks.nl/getdoc/0f25cfe4-9965-40f2-8a8a-bf4e2fcf7de7/Power-DC-X-terminator.aspx#pdcxcplus but big $$$ involved so I decided to give DIY a go.

Based on Main DC Blocker circuit by Rod Elliott from http://sound.westhost.com/articles/xfmr-dc.htm and by Mark at http://theartofsound.net/forum/showthread.php?11219-DIY-DC-blocker I have created both circuits, each based on each of these designs.

The design from Rod Elliott seems to block DC less than 1-1.2 Volts and one from Mark can block all DC voltage. The Mark's suggestion is simpler. Both have been tested and works well for my system (consuming about 300watts, 1.7A) but eventually I use the one based on Mark's suggestion. It simply works for any DC offset in terms of voltage.

Buying parts from element14 (waiting for about 2 weeks).

I decided to mod the old Consonance PW1 (http://www.osbornloudspeakers.com.au/opera/pw3.html) which already has RFI filter function and 10A fuse by just adding DC blocking circuit after the RFI one.

Below are some photos. I would recommend the Mark's suggestion. It works for me so it should work for you if you have DC offset problem in your main AC power.

Edited December 12, 2014 by Tam Nguyen

[JDWest]

Well done!  It prompts several questions, probably ending with "would you build one for me" 

 

How to measure whether you have a DC offset?

 

Looks like you have a P10 Power Plant. Does that not remove DC?

 

Did you notice any improvement in sound quality?

 

Cheers,

 

John

[MrBurns84]

Excuse my ignorance, but how can one tell if they have a dc problem in thier system?  thanks

[andyr]

The power at my area has DC offset so the need to block DC offset is high.

Based on Main DC Blocker circuit by Rod Elliott from http://sound.westhost.com/articles/xfmr-dc.htm and by Mark at http://theartofsound.net/forum/showthread.php?11219-DIY-DC-blocker I have created both circuits, each based on each of these designs.

The design from Rod Elliott seems to block DC less than 1-1.2 Volts and one from Mark can block all DC voltage. The Mark's suggestion is simpler. Both have been tested and works well for my system (consuming about 300watts, 1.7A) but eventually I use the one based on Mark's suggestion. It simply works for any DC offset in terms of voltage.

Hi Tam,

 

I went to your 2nd link (art of sound) but couldn't find a definitive circuit diagram, - would you mind sketching the circuit of what you have actually built and posting it?

 

I have built the Rod Elliott one and that certainly works - but I would be very interested to try out the one you are using.

 

 

Thanks,

 

Andy

[andyr]

Excuse my ignorance, but how can one tell if they have a dc problem in thier system?  thanks

 

At the simplest level ... you might have mains transformers buzzing.

 

However, this is more about what you hear when you put a DC blocker into your system (between a component and the wall) ... kind of like what you see when you've had your windows cleaned.

 

Andy

[Tam Nguyen]

It is not easy to measure DC on mains and to be honest I don't have the right equipment to measure it, didn't measure it and cannot measure it.

 

Andy is right. You can tell you have DC offset by the mechanical hum within your amp's transformers or in my case even P10 transformer, especially when inverter air-con, centralised heater or dish washer is on and running  . Not excellent transformers have steady mechanical hum. If you have a good transformer and no DC offset present you won't hear any hum. But with DC offset in your main, you can hear transformer hum at times, not all the time, especially when DC level is high. That's how you know and feel you have DC offset.

 

I read and know that toroidal transformers over 500 VA are very susceptible to DC offset.

 

John, unfortunately P10 cannot remove DC and it suffers from DC offset actually though PSaudio website states different thing. When I bought P10, I didn't think of DC offset until it showed this DC offset problem to me.  P10 has a big toroidal transformer to step down 240 VAC before doing AC-DC conversion so basically, theoretically it blocks DC (its transformer blocks DC). However, this toroidal transformer gets hum by DC offset then when my air-con/heater is running, very noticeable  . That is the reason I had to make this one to protect P10. I am not much worried about the hum within transformers of my amps because they are behind P10 and the output from P10 is quite pure AC.

 

John, I don't  notice any improvement in sound quality because I have P10. I just made this one to protect the P10 from DC offset.

 

Andy, the Rod Elliott one should work fine because I read somewhere and they mentioned DC offset over 1 V is rare case and considered very bad. I don't think we all have that bad in Australia. So basically Rod Elliott one uses 2 diodes in each direction of AC and should bocks 1-1.3 V DC. I think that is enough. And besides setting voltage for the caps,  if something wrong with the capacitors or when the caps cannot handle big current, the diodes in Rod Elliott would take over so it is quite safe, I think.

 

I think Vibex one (at 6moom review) has quite the same circuit as Rod Elliott one. PSAudio used to have humbuster iii and I think it has the same circuit as well.

 

Personally I like the Artofsound better because the feeling of getting rid of DC completely. But I would use bigger electrolytic capacitance caps with high voltage rating, high current rating and small ESR for Artofsound one just to be safe. My Consonance PW1 does not have more space for more caps and a soft start circuit to protect inrush current so I have to be content with the implementation I have done. I have a tendency to "over-engineer" to be safe. But with my 300 watts system, this one is more than OK, I believe.  From  Rod Elliott one's calculation, it is safe to use 3000uF (for each cap in the anti-parallel pair of caps) for each 500mA. So for current of 1.5A, it is safe to use 10000uF electrolytic caps in a anti-parallel pair or many smaller pairs in parallel (like Vibex) depending on the space of the box.

 

I have added the art of sound diagram.

 

John, making each circuit took me less than 2 hours but the preparation (waiting for parts - my parts came in 4 separate deliveries just for 4 caps, some diodes and some diode bridges, planning to fit the PW1, modifying the PW1 box etc,) was painful , especially the wait and counting the days for delivery. . I would not want to go thru the pain one more time:).

 

Cheers,

 

Tam

Edited December 12, 2014 by Tam Nguyen

[valvedude]

The power at my area has DC offset so the need to block DC offset is high.

Some solutions available for 240V of Australia such as http://www.6moons.com/audioreviews/vibex/2.html ; http://www.kempelektroniks.nl/getdoc/0f25cfe4-9965-40f2-8a8a-bf4e2fcf7de7/Power-DC-X-terminator.aspx#pdcxcplus but big $$$ involved so I decided to give DIY a go.

Based on Main DC Blocker circuit by Rod Elliott from http://sound.westhost.com/articles/xfmr-dc.htm and by Mark at http://theartofsound.net/forum/showthread.php?11219-DIY-DC-blocker I have created both circuits, each based on each of these designs.

The design from Rod Elliott seems to block DC less than 1-1.2 Volts and one from Mark can block all DC voltage. The Mark's suggestion is simpler. Both have been tested and works well for my system (consuming about 300watts, 1.7A) but eventually I use the one based on Mark's suggestion. It simply works for any DC offset in terms of voltage.

Buying parts from element14 (waiting for about 2 weeks).

I decided to mod the old Consonance PW1 (http://www.osbornloudspeakers.com.au/opera/pw3.html) which already has RFI filter function and 10A fuse by just adding DC blocking circuit after the RFI one.

Below are some photos. I would recommend the Mark's suggestion. It works for me so it should work for you if you have DC offset problem in your main AC power.

thats a voltage doubler circuit lol

[valvedude]

i thinks i a good way to catch you house on fire better hope you have fire insurance 

 

new too me DC on the mains i better ring my energy company 

 

if you check you mains with a CRO you will see it AC = alternating current at 50 HZ 

 

http://www.animations.physics.unsw.edu.au//jw/power.html

 

http://en.wikipedia.org/wiki/Voltage_multiplier

 

 

 

340 Volts

 

The peak-to-peak voltage of this sinewave is the RMS voltage multiplied by 1.414 (the square root of 2). If we assume the RMS voltage to be 240 Volts, the voltage from one peak of the sine wave to the other is 240 * 1.414 or 340 Volts.

Edited December 13, 2014 by valvedude

[Tam Nguyen]

Valvedude, before you lol and conclude, you better read carefully Soundwest and Artofsound links and do homework than googling and copying some articles not related. Your first link on AC sine wave is for those who has no knowledge on electrical wants to learn a bit. The diodes are there to set the voltage on the caps at diode forward voltage. For Rod's one, it is max 1.3V on 2 diodes, the rest of 240V will drop on load, not 240V on the caps. Rod explains in his web link above carefully and easy to understand. It is based on electronics calculation. If you have some basic knowledge in electrical and electronics, it is not hard to understand Rod's circuit. Mark even makes it better. Each has pros and cons. Hifi makers who make these DC blockers also do similar to that, no magic and sell for big $$$ and they use even smaller caps to cut cost. Some focus on marketing points as quality of box material, wire, copper etc. which is nice to have in this power application. If the box is small, no way they have big caps inside. Dyi for these simple things is fun and we can spend money in good parts for safety rather into hifi maker marketing costs. We give credits to those who design the circuits and explain the rationale behind them so we can use them to diy. Besides, the caps are in series with the load so 240V RMS will split between the caps and the load (240 = v1+v2) In this application, big capacitance is important when your load draws big current ( I = V/Xc; C=1/2*3.14*50*Xc). Caps with low ESR is

better to keep heat on caps low. If electrolytic caps are too hot, their lives are short. It is not like in some big DC power supply applications

where caps are parallel with load and requires caps with high working voltage ratings i.e. 400V but not big capacitance. The links you attach here have nothing to do in this case.

Besides, these caps used here are with 80V ratings and 7A ratings. If needed, use more pairs of caps in parallel to increase current rating or use bigger caps, i.e 22000uF. More than necessary. Energy company can do nothing with DC offset caused by modern home appliances unless you and your neighbours stop using most of them.

If the design is wrong, the caps or diodes will pop the moment you plug 240V power to it.

Edited December 13, 2014 by Tam Nguyen

[Tam Nguyen]

Besides, if DC offset on Main AC is something new to you, googling that keyword and you even find some articles by universities as well. If you have enough knowledge on electrical, physics and maths to read thru them, read thru those articles by universities. Otherwise pick articles which explain for everybody not for engineers

Edited December 13, 2014 by Tam Nguyen

[valvedude]

well hi i read the info i still i am bamboozled

 

 i read and picked through the information  

 

i did my electronics course in tv and demesne  audio and at NO time was i told there would be a DC blocking circuit need on the mains and or i would find some and portions amounts of DC on the Australian mains at 240 volts 50 HZZ 

 

2nd of all why would there be small amount of DC present on the mains 

 

3rd i have been in the electronic field EG domestic electrons pro electronics and white goods 

 

ok my step father is an electrical engineer i will forward the documents to him and ask his opinion

 

 3rd i am wonder who had the data and the statistics on this if some one con forward dossier  or is it just an audio file thing 

Edited December 13, 2014 by valvedude

[andyr]

Comments below:

 

well hi i read the info i still i am bamboozled

 

 i read and picked through the information  

 

i did my electronics course in tv and demesne  audio and at NO time was i told there would be a DC blocking circuit need on the mains and or i would find some and portions amounts of DC on the Australian mains at 240 volts 50 HZ

1. How many decades ago did you do this course?
2. Have no idea what "demesne  audio" is but I don't find it extraordinary that all the arcane things that audio-obsessives are interested in was not covered in your course.  Did they also talk about:

* the importance of absolute phase in audio reproduction?

* the audible effects of using different-guage signal wire?

* making sure the primary circuit of a power transformer is correctly connected, vis-a-vis active & neutral?

* etc.

 

2nd of all why would there be small amount of DC present on the mains 

 

If you bothered to explore the other threads on SNA about DC on mains you would've found that it appears because of people's use of:

• solar converters (maybe there was no such thing when you did your course?).
• electronic light dimmers and fan controllers
• etc.

Not necessarily your use - it could just as well be your neighbour's.

 

3rd i have been in the electronic field EG domestic electrons pro electronics and white goods 

 

And so?

 

ok my step father is an electrical engineer i will forward the documents to him and ask his opinion

 

Please let us know his opinion.   Given he's (presumably?) a lot older than you, I would suggest he probably knows little about this sort of thing either, as it's an "audiophile" thing ... not an electronics/electrical engineering thing.

 

 3rd i am wonder who had the data and the statistics on this if some one con forward dossier  or is it just an audio file thing 

 

All I can say is - and a number of folk on this Forum would deride this, as we only used 1 half-blind guy in the tests, so it wasn't a "Double Blind Test" - that you can hear the difference when DC is blocked.  All you need to do is try it out!

 

 

Regards,

 

Andy

Edited December 14, 2014 by andyr

[Tam Nguyen]

Valvedude, some courses cannot cover everything and even if you are in 4-5 year electronics course at an university, nobody can teach you everything .

 

This is not just audiophile thing.

 

Let me give you an academic article to read.

 

 

DC offset.pdf

[valvedude]

Comments below:

 

 

 

Regards,

 

Andy

not sure about your comments how old do you think i am you must think i am a dinosaur  

 

yes wire gauge i do under stand it and ohms law etc 

 

i build valve audio amplifiers and preamps

 

so with this DC on the mains i have worked on  mark levinson amplifiers Quad Quaested monitors QSC  nakamichi luxman and many others  and i not seen any DC blocking circuits 

 

yes other people will and do know more then i do this was not about dick measuring i was making comments on what i knew

 

i was supplied a document to read 

 

as i said in my other post my step father is an electrical engineer  i will all so ask his option as to the issue 

1. i work as an audio technician
2. i will reiterate as i said before  i have never read and or have never  been  told about DC on  the AC mains
3.  sorry its a typo i work as an electronics technical in the professional and the domestic side of things 
4. i work with 3 phase and signal AC wiring etc  

Edited December 14, 2014 by valvedude

[Addicted to music]

http://eprints.usq.edu.au/8224/

 

https://www.google.com.au/search?sourceid=navclient&aq=&oq=&ie=UTF-8&rlz=1T4PLXB_enAU595&q=dc+offfset+on+pv&gs_l=hp..0.41l158.0.0.0.2558...........0.

 

Interensting read!

[valvedude]

http://eprints.usq.edu.au/8224/

 

https://www.google.com.au/search?sourceid=navclient&aq=&oq=&ie=UTF-8&rlz=1T4PLXB_enAU595&q=dc+offfset+on+pv&gs_l=hp..0.41l158.0.0.0.2558...........0.

 

Interensting read!

i think so too lol 

[Woodear]

Hi Tam

 

Interesting post and am definitely interested.  Would you be able to post an Elements 14 parts list please? 

 

Thanks.

[TMM]

I hope you aren't powering anything high-power from that. Those caps are probably only good for 2-3Amp continuous AC for a few thousand hours before they fail.

 

The creepage distance on that strip board is also pretty marginal and trace widths are not appropriate for the currents involved. What makes it worse is that it is sandwiched against some cardboard. All it takes is a spike on the line to flash over and you have a fire.

 

If you can't make a proper PCB, It would be better to just get rid of it and air-wire everything. Instead of a piece of cardboard use a sheet of plastic or fibreglass PCB material with the copper layer stripped off.

 

Besides, these caps used here are with 80V ratings and 7A ratings.

I doubt they are 7A in this application. The rating is usually quoted for 100KHz and there is a significant derating factor for 50Hz usage - it could be less than half of the 100KHz rating.

 

 

Valvedude, some courses cannot cover everything and even if you are in 4-5 year electronics course at an university, nobody can teach you everything .
 
This is not just audiophile thing.
 
Let me give you an academic article to read.

 

Pretty much none of that was relevant to this thread. It was an article about how to design a solar power inverter (a device that converts the DC output from a solar panel installation into to 240V AC) to minimise the DC component that it injects onto the 240V AC power grid. No where did it have anything to do with removing DC that already exists on the 240V AC grid.

DC offset exists on the AC power grid primarily due to devices that draw more current on the positive half cycle than the negative half cycle (or vice versa). Grid tied inverters would account for a very small contribution indeed.

Edited February 9, 2015 by TMM

[Graham D]

Hi Andy

I have a DIY Geddon clone powering my turntable with a 500va toroidal transformer which has a very faint hum I would like to eliminate.

If I was to build Marks version of DC Blocker can you advise what value caps I should use and where to source them in NZ or Australia ?

As they are exposed to full mains power I presume they must be rated at 240 volts or higher.

 

Cheers

Graham

[JPete9]

If anything needs an actual trades person its 240v

 

https://www.youi.com.au/youi-news/will-diy-electrical-work-affect-my-insurance

 

I can easily do my own 240v - its 3 wires! and I have done when i was younger and dumber. But once you think about what life might be like after you accidentally electrocute some one or burn your home down and get no insurance...the risk doesnt seem worth it.