Correct Fitting of DC Blockers

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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".
 
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.
 
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)
 
The reason I use them on my DIY HiFi equipment is because other transformers in my house buzz, so I've assumed that there is DC on the mains. Can I just put my multimeter in DC mode and put it across the live/hot & neutral and measure it that way?

Despite other buzzing transformers around the house, my audio equipment with the DC Blockers has never buzzed. I've been using the DIY HiFi Supply model on smaller Transformers, but was always confused by their fitting instructions, hence this thread.

I'm just about to install a Sjostrom Audio DC02 Blocker onto a larger transformer for my Beta 22 Headphone Amplifier. I've just built it up, it's a very high quality PCB.
 
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