DIY DC blocker?

[HighFidelityGuy]

I've just stumbled across THIS info about building a simple DC blocker to reduce mains transformer hum. I currently have some issues where my valve amp tranny runs hot and my sub trannies intermittently buzz to varying degrees through the day. So I'm thinking I may have a DC offset issue on my mains. I was hoping the Belkin PF30's I bought would get rid of this but they don't and neither does my Tacima mains block. So perhaps this may help instead. I have the parts in my spares box to build one to try.

Here's the schematic:



So I was wondering if anyone had built one of these and what your thoughts are on it's effects both positive and negative?

Cheers.

[Reid Malenfant]

Well that circuit is a waste of time, it won't block DC at all



If you look at the way the diodes are wired you''ll see that DC over 1.2V can still flow

[Reid Malenfant]

Take out D4 & D5 & then connect the centre of the diodes to the centre of the capacitors & it'll work. The diodes are there to block DC & prevent high reverse voltages on the capacitors

[HighFidelityGuy]

Like this?:



That design is from HERE. This guy mentions that putting an extra two diodes in will make it block more DC. So that's why I thought the first schematic was the way to go. So if adding two more diodes will improve it, how should I wire them?

Cheers.

[Reid Malenfant]

In your second diagram turn the two doides the other way round, you need them to short out any reverse voltages greater than 0.7V accross the electrolytics I'd suggest using at least 16V electrolytics so any reverse voltage is really low compared to the capacitors forward voltage capacity. We don't want them going bang now do we

Whoever designed the first one needs to stick to his day job

Feck me, whoever designed the second one needs to stick to the day job to

Who are these people? If you are blocking DC you can't block MORE! I'd suggest you use fast soft recovery diodes to do the job, 1N5404 is only rated to 3 or 4 Amps, get some big 30A devices in there

[Reid Malenfant]

In fact i have just the thing MUR3040PT & you'd only need one device as they are a dual diode package.

[HighFidelityGuy]

Ok you've lost me now.

So from this diagram you're saying I need to turn the diodes the other way round but the MUR3040PT has it's diodes oriented in the way shown in the diagram, so how can I turn them round?

[Reid Malenfant]

Turn the capacitors the other way round Dave

[MCRU]

I have a dc blocker made and on a pcb, rated at 5 amps, want one to try?

designed and built by nick (lurcher) on my behalf and thoroughly tested both on a live mains and on a pc simulation.

[HighFidelityGuy]

Turn the capacitors the other way round Dave

Ah, clever. So like the attachment below then?

I have a dc blocker made and on a pcb, rated at 5 amps, want one to try?

designed and built by nick (lurcher) on my behalf and thoroughly tested both on a live mains and on a pc simulation.

Thanks David, that would be awesome. How would you want to work the trial? Just drop me a PM with details and we'll work something out.