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D C Blocking on mains supply

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warning - do not attempt this without a very competent knowledge of what is involved and the safety required.

I have been interested in the blocking of dc voltage coming in on the ac mains line for some time and after a discussion with a client who is the head of foxtel engineering regarding devices which contaminate the mains supply entering our houses, I decided to build a very simple outboard dc blocking distribution box for exactly that purpose. the schematic was courtesy of rod elliots excellent website and the components all courtesy of rs components so nothing to exotic, iec input from furutech and mains sockets from hpm. all blocking modules were assembled and slowly brought up to 240 volts using a variac as exploding capacitors are best not experienced and everything worked as hoped and after final assembly, rechecked again and soak tested under load. all good.

2 types of use were envisaged, for visual components and for audio.

firstly, dc voltage on the ac line is very common these days as components using switch mode power supplies have a degree of cause and even more recently, solar panelling and the associated inverters. dc on the ac line has a tendency to cause transformers to run hotter and noisier being the main issue.

on the visual side when inserting this device in line with the mains supply to the plasma we have at home showed a quite remarkable improvement in picture colour, stability of image, white noise level or blackness depth and the amount of heat generated from a 5yr old NEC50 plasma. can't watch anything now without it being in line. the depth of the black's reminded me of the best pioneer plasma's and I would not be surprised if their reputation was based on an internal dc blocking device as the effect on the black's and colour intensities was certainly similar.

as for sound reproduction on a modest system, the results were likewise positive with a quieter background noise being most evident and with transformers running considerably cooler.

more listening to be done but at this stage, all very positive.

cheers, g.

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Nice work -well done

I hadn't realised DC was an issue, and we've got solar panels on the roof, so a close offender.

Mike

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warning - do not attempt this without a very competent knowledge of what is involved and the safety required.

 

I have been interested in the blocking of dc voltage coming in on the ac mains line for some time and after a discussion with a client who is the head of foxtel engineering regarding devices which contaminate the mains supply entering our houses, I decided to build a very simple outboard dc blocking distribution box for exactly that purpose. the schematic was courtesy of rod elliots excellent website and the components all courtesy of rs components so nothing to exotic, iec input from furutech and mains sockets from hpm. all blocking modules were assembled and slowly brought up to 240 volts using a variac as exploding capacitors are best not experienced and everything worked as hoped and after final assembly, rechecked again and soak tested under load. all good.

 

2 types of use were envisaged, for visual components and for audio.

 

firstly, dc voltage on the ac line is very common these days as components using switch mode power supplies have a degree of cause and even more recently, solar panelling and the associated inverters. dc on the ac line has a tendency to cause transformers to run hotter and noisier being the main issue.

 

on the visual side when inserting this device in line with the mains supply to the plasma we have at home showed a quite remarkable improvement in picture colour, stability of image, white noise level or blackness depth and the amount of heat generated from a 5yr old NEC50 plasma. can't watch anything now without it being in line. the depth of the black's reminded me of the best pioneer plasma's and I would not be surprised if their reputation was based on an internal dc blocking device as the effect on the black's and colour intensities was certainly similar.

 

as for sound reproduction on a modest system, the results were likewise positive with a quieter background noise being most evident and with transformers running considerably cooler.

more listening to be done but at this stage, all very positive.

cheers, g.

 

Very nice, guru.

 

So this device goes between the wall plug and the component, right? :confused:  (Well, actually 4 components, in your case?)

 

Shirley, though, a 1:1 isolating transformer will also block DC?

 

 

Regards,

 

Andy

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Guest guru

Correct Andy as to it's location and even though I have an isolation transformer somewhere, this was an experiment were the blocking components for each outlet cost less than $20 so it could be deemed as a mild distraction with very positive results. The improvement in picture quality was such that I sat and rewatched "a bug's life" yesterday morning due to the difference in screen quality alone. Go figure, as I said, all courtesy of mr Elliot's very informative website.

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Hi guru,

 

Thank you for reporting back the result. Very informative and useful, not to mention what a nice work you did there, quality build! I am sure many DIYers appreciate this.

 

Cheers,

William

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Beautiful built.

Now I have another thing on my to do list.

Thanks for sharing.

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Nice one guru. I am glad that it works for you. There are many discussions on diy forums for noisy transformer solutions but does not seems always to work.

Quan

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I find that most, if not all of these devices clean up the power, resulting in lower noise floor but at a cost of body and warmth, often the sound becomes a little more sterile and opaque. Using Diodes is also a problem. In a superbly well tuned system, i find its nearly always a backward step.

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Correct Andy as to it's location and even though I have an isolation transformer somewhere, this was an experiment were the blocking components for each outlet cost less than $20 so it could be deemed as a mild distraction with very positive results.  Go figure, as I said, all courtesy of mr Elliot's very informative website.

 

Yes, I'm a big fan of Rod's site - I've been using his XO PCBs for about 12 years, now.  :thumb: 

 

Now, this device prevents DC on the mains from passing though.  Do you think it would work in the "reverse direction" ... ie. stop a component whose PS was producing DC (in my case, a 33/45rpm speed controller) from injecting this into the mains?  I have this peculiar problem which I am trying to solve.  As soon as I power my TT from the 33/45 speed controller (so I can get 45rpm), I hear a LF warble in both channels (TT straight into the wall (so only 33rpm) - no problem). :(  Yes, I could try an isolation transformer ... but I don't happen to have one - so this cheap device sounds interesting. :)  Of course the problem may not be DC! :(

 

 

Regards,

 

Andy

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Nice work -well done

I hadn't realised DC was an issue, and we've got solar panels on the roof, so a close offender.

Mike

 

The visible effect of Mains DC is vibrating transformers. In my case it's pretty bad that actually the enclosure gives out audible hum at my listening position !!

 

I use this circuit successfully:

http://sound.westhost.com/articles/xfmr-dc.htm

 

xfmr-dc-f8.gif

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