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Old 21st July 2012, 06:52 PM   #1
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Default Correct Fitting of DC Blockers

Hi Everyone,

I've got one of these DC Blockers from DIY HiFi Supply, I find the fitting description quite confusing, it says in the instructions to put it on the neutral side, yet in the picture it appears to be on the live/hot side:

DC Blokker Module | Diy HiFi Supply

Does anyone have any advice on which is the correct side to fit the blocker?

Many thanks for any assistance.
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Old 21st July 2012, 07:15 PM   #2
Did it Himself
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It does not matter as it is a series circuit.
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Old 21st July 2012, 09:05 PM   #3
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Many thanks, I'll get building!
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Old 21st July 2012, 10:02 PM   #4
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Does anybody know what hides in the mold?
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Old 22nd July 2012, 06:07 PM   #5
DF96 is offline DF96  England
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Capacitor and/or some diodes.
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Old 22nd July 2012, 08:55 PM   #6
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I am not going to build one as I do not think a few volts of DC are going to saturate my transformer. But would it not take a C in the range of 1000s of uF to keep voltage drop low? And can you please explain how diodes can help? Antiparallel? Isn't that just subtracting 0.7V in both polarities? I read about a DC eliminating device by Burmester that involved a lot of semis and also claimed to lower the impedance!! of the mains. It was said to load the mains during the bigger half wave. A giant "AC shunt regulator".
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Old 22nd July 2012, 09:05 PM   #7
DF96 is offline DF96  England
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Yes, big caps are needed so back-to-back electrolytics with steering diodes is one option. Some people claim that a simple shorted bridge (so two diode drops) is sufficient on its own, but I am not convinced. I think if I needed a DC blocker I would use a biased electrolytic, with bias obtained from the AC supply.

A few volts of DC could disturb a low resistance transformer, like some toroidals. Remember, all DC sees is the primary resistance and there is no cancelling current in a secondary to reduce DC flux.
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Old 23rd July 2012, 12:51 AM   #8
dangus is offline dangus  Canada
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I think it falls into the category of devices that work equally well whether you wire them into a circuit or leave them in the box.
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Old 23rd July 2012, 03:54 AM   #9
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by astrouk1 View Post
Hi Everyone,

I've got one of these DC Blockers from DIY HiFi Supply
Maybe a good idea might be to MEASURE the amount of DC current in your mains wall outlets before investing in a large capacitor.

Even if there were a few milliamps of DC the effect is only that the effective size of the power transformer is reduced

The next question is if these things are even legal. Seriously. I doubt it is an X or Y rated cap and I _think_ (?) it needs to be if it is connected to the primary side of a transformer. Or is that only if the cap is in parallel and this is series?


Next, I wonder what problems this might introduce. With the primary you now have a series LC. Will it oscillate? What about inductance of the cap and ESR?

One other question. Every large cap has a rating for max "ripple current". I wonder what is the rating of the cap inside the box. Certainly being connect in series with the mains it will see "ripple" (that is kind of an understatement)
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Old 23rd July 2012, 03:59 AM   #10
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by dangus View Post
I think it falls into the category of devices that work equally well whether you wire them into a circuit or leave them in the box.
No, I'm thinking it might be measurably better to leave it in the box. This gadget is basically a "high pass filter".
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