Mains DC Blocker

[Ammonite Audio]

Has anyone used or built the mains DC blocker module from Sjöström Audio? Details at http://sjostromaudio.net/shop/mains-circuits/60-dct02-dc-filter-for-toroidal-transformers-built-unit.html . This looks like a very reasonably priced product, but I'd be interested to know how it may compare to commercial DC blockers, like those from Kemp, MCRU etc.

My mains clearly has a varying DC element - the big toroid in my Hegel amp does sing along to whatever is on the mains, and I'd like to hear what removing DC offset does, without comitting myself to a ready-made retail product.

[Colin Wonfor]

No I use my own design which has component and user protection, and has a lower line impedance which reduces loses in heat.

[Ammonite Audio]

No I use my own design which has component and user protection, and has a lower line impedance which reduces loses in heat.

Can you tell me more?

[Barry]

Can you tell me more?

This might be of interest: http://sound.westhost.com/articles/xfmr-dc.htm .

[Ammonite Audio]

I'd seen that and read a load of other stuff too to understand how these things work, but a totally DIY build is not something that I want to do with mains voltage involved, hence mentioning the convenient Sjöström Audio module. I can populate a PCB, connect it up and mount it is a suitably safe enclosure, but that's all. Hopefully Colin will be along with some details of his design, which sounds intriguing.

I am becoming increasingly conscious of the safety and insurance ramifications of audio tinkering and tweaking. Presumably a DC blocker from Kemp or LDA complies with all relevant electrical safety regulations, but buying a totally built solution does ramp the cost up.

[sq225917]

I run two of the sjolstrom units. They work well, taking upto a couple of volts of dc out of the mains. Worth checking to make sure it's dc on your mains and Moy varying 2nd and 3Rd harmonic from a nearby large three phase user.

And there's no heating to speak of with the sjolstrom unit. Not sure what Colin is trying to infer there.

[Ammonite Audio]

I run two of the sjolstrom units. They work well, taking upto a couple of volts of dc out of the mains. Worth checking to make sure it's dc on your mains and Moy varying 2nd and 3Rd harmonic from a nearby large three phase user.

And there's no heating to speak of with the sjolstrom unit. Not sure what Colin is trying to infer there.

Thanks for that. Do you use them generally for the whole system, or just on equipment like power amps? In other words, what's the intelligent way to use these things?

[danilo]

Merely Curious here. Is the Mains power inna UK Really? that excreable?
Wind and coal power not what it's claimed to be ?

[Ammonite Audio]

The DC offset arises either in the home from other appliances, or from other households sharing the same local mains supply phase. I have no doubt that the power coming out of the National Grid is as clean as it's possible to be.

[Ammonite Audio]

I've ordered one of the built Sjöström DC blocker modules, based on Simon's recommendation above. It's inexpensive, so worth a pop to see if these things are going to be of benefit in my house.

[Yomanze]

DC on the mains was playing havoc with my balanced mains transformer, looks like one of these will sort that.

[sq225917]

I used one on my power amp and the other is on my TT-psu, but only because it used to be on my previous tt-psu which employed a 500 VA toroid and was upset by dc easily.

[Yomanze]

Hmm yeah my 1.5kva balanced transformer was not happy with DC on the mains. It actually made the sound worse, hence why I took it out. It worked much better in my old house, maybe time to try again.

[anthonyTD]

Interesting article Barry, for those especialy, who want to get an understanding of what is actualy happening, and why, although, i suspect most will just want a quick fix!
This might be of interest: http://sound.westhost.com/articles/xfmr-dc.htm .

[Carlos-UK-2016]

This might be of interest: http://sound.westhost.com/articles/xfmr-dc.htm .

Barry, I found an assembled product that links to the article that you suggested. Can you cast your eye on this one & let me know your thoughts, please?
http://www.ebay.co.uk/itm/131654666919

DC Blocker is built with following parts:
- two 15 000 uF EPCOS capacitors
- four high-voltage diodes HER605
- one 10W power resistor
- one WIMA MKS4 400VAC capacitor
- two MOLEX 3-terminal connectors for AC input/output
- one PCB for DC Blocker.

http://rootscript.com/_AOS/dcb1/dcb1-schematic-960.jpg

http://rootscript.com/_AOS/dcb1/dcb1-board-960.jpg

http://rootscript.com/_AOS/dcb1/dcb1-assembled-960.jpg

thank you
:)

[Barry]

Hello Carlos,

It looks good to me; the capacitors are rated at 50V which should be OK and the diodes seem to have sufficient current rating (though I will have to check).

[sq225917]

That's basically the same circuit as the sjolstrom

[Wakefield Turntables]

I've just gone and bought three of these to have an experiment with my systems. :eyebrows:

[Simon_LDT]

I've just purchased one too. Worth a try to lesson the transformer hum from my monoblocks.

I've just noticed though that the AC output plug is in an awkward position as I don't believe there will be enough room for cable clearance.

[Colin Wonfor]

I use this circuit with filters.

The main blocking caps are 2.5 Farads low volts and I do not allow them to be reversed biased more than 0.6VDC, choosing such large caps my seem silly but it works and it does keep the impedance low less than 10mΩ. And means they at high current lets say 10A will only dissipate 1W. and 2500uF will dissipate about 6.5W not good.

http://i1148.photobucket.com/albums/o580/colinwonfor1/DC%20BLOCKER_zpsw0q3usve.jpg

[Ammonite Audio]

That's basically the same circuit as the sjolstrom

The Sjöström DC blocker uses 6 diodes, rather than 4. I've no idea if 6 diodes means a better circuit.

[Ammonite Audio]

I use this circuit with filters.

The main blocking caps are 2.5 Farads low volts and I do not allow them to be reversed biased more than 0.6VDC, choosing such large caps my seem silly but it works and it does keep the impedance low less than 10mΩ. And means they at high current lets say 10A will only dissipate 1W. and 2500uF will dissipate about 6.5W not good.

http://i1148.photobucket.com/albums/o580/colinwonfor1/DC%20BLOCKER_zpsw0q3usve.jpg

Maybe it's just me, but every mains filtration device that I've heard which uses series chokes has a negative effect on musical replay. I know that designs involving series chokes are technically more 'effective' at cleaning up mains crud than simpler parallel filters, but until someone shows me otherwise, I reckon that they throw too many babies out with the proverbial bathwater. What's the general view here?

[Carlos-UK-2016]

Hello Carlos,

It looks good to me; the capacitors are rated at 50V which should be OK and the diodes seem to have sufficient current rating (though I will have to check).

Thanks for your advice Barry.

I have a question about where to place these DC Blockers.
Would they be connected just before the amplifier?
OR
Would they be placed before a device that might be 'leaking DC' back into the AC supply?
OR
Is my question silly? :)
thanks (got a really bad headache today - I'm really not thinking clearly today)

I'm not an electric type guy, so this is my silliest question (today): How would one safely measure if there is DC leaking?
I had the silly idea that an improved DC blocker might be able to be 'switched on' only when DC is detected on the AC line, OR is the amount of 'blocking' adjustable based on the amount of DC. (If DC Blockers might be detrimental to the overall sound of an amplifier, can an improved version be switched on when needed, and the amount of 'blocking' adjusted) - Please don't laugh too hard at me :scratch:

[CageyH]

I have mine fitted just before my amplifier.

[Carlos-UK-2016]

I have mine fitted just before my amplifier.

Thanks Kevin.

One thing that I have been searching for which might seem simple to some of you guys, is How to measure if you do have an issue with DC on your AC mains.

I found this article, which I would like to ask you guys for advice on. It suggests measuring DC using a multimeter on the speaker terminals of your amplifier.
Since I use integrated tube amp, I am worried about running the tube amp without the speakers attached (without a load).
Here is the link: http://www.wikihow.com/Measure-DC-Offset

It may be a basic question, but is this the ONLY way to measure for DC problems, or do you guys use other methods also. I would be really useful to some of the people with less experience (people like me), if you more experienced guys could give a few options of how to measure DC offset etc... so that we can see if we have issues, and so that we can see that where we might be adding DC Blockers, that the 'fix' has some concrete effect.

thanks

[NRG]

Measuring for DC on your speaker terminals won't tell you if you have DC on the mains! They are two separate measurements. A valve amp with an output transformer should not have any DC on the speaker terminals. I measured my mains using an oscilloscope. Edit, Oh you will need a capacitor and resistor filter cct to take the measurment from.

[lurcher]

DC on the mains supply will not cause DC on the output of a SS amplifier. The issue of DC offset from a amplifier can be a issue but is not in any way related to offset AC from the mains.

If you have a valve amplifier with output transformers, unless they do something rare there will by definition be no DC on the output terminals as you are connecting to the secondary of a transformer. Transformers will not pass DC.

Edit: Neal got there first :-)

[Carlos-UK-2016]

Thanks for that info Nick & Neal, it really helps :)

I use an AC regenerator (AG500) that has six outputs (I believe it converts AC to DC and back to AC to clear out any DC problems). I plug in all my audio equipment to this unit for power.
I play my flac music files on a Mac Mini which has an internal SMPS, and I think it may cause problems; so I wanted to try to isolate it (the Mac Mini) from the 6 outputs from the AC regenerator, while still feeding the Mac Mini a stable 230v from the regenerator. I was hoping to put a DC Blocker before the Mac Mini so that DC doesn't cross back to the clean AC regenerator (If that makes sense?), I am not sure if that is the right option to try, any thoughts on this? :scratch:

Notes: Also, plugged into the AC regenerator are: DAC & REL subwoofer & SET tube amp.
The DAC has a separate power supply & is connected to Mac Mini with USB cable. The DAC is connected to tube amp with RCA interconnects.

I have been thinking about removing the internal SMPS from the Mac Mini, and replacing it with the Uptone MMK kit (which will allow me to use a linear power supply (LPS) with the Mac Mini), but I wanted to try a DC Blocker first. Link to Mac mini DC-Conversion / Linear Fan Controller Kit (MMK): http://uptoneaudio.com/products/mac-mini-dc-conversion-linear-fan-controller-kit-mmk

[NRG]

What makes you think the Mac mini is putting DC onto the mains? If you want to isolate it plug it into a separate mains socket! The regenerator will continue to filter the mains for all your other devices.

[lurcher]

You could make a 230v : 230v isolating transformer out of two 230v:9v 100va transformers back to back. The resulting AC will be less than the 230v in, but the SMPS will deal with that, and it will isolate any DC offset the SMPS is adding from the regenerated AC.

[Carlos-UK-2016]

What makes you think the Mac mini is putting DC onto the mains? If you want to isolate it plug it into a separate mains socket! The regenerator will continue to filter the mains for all your other devices.
Neal,
The Mac Mini internal SMPS is notorious for being super dirty. I have now plugged it into a separate mains socket (leaving my other audio devices 'protected' by the AC regenerator) as you suggested - THANKS :)
I will look at the Uptone MMK Linear Power Supply kit (when I have some spare cash). :(


You could make a 230v : 230v isolating transformer out of two 230v:9v 100va transformers back to back. The resulting AC will be less than the 230v in, but the SMPS will deal with that, and it will isolate any DC offset the SMPS is adding from the regenerated AC.
Nick,
That is a another option. In my current DIY mood, I am willing to have a go at anything, If you have time could you post a link to a suitable pair of transformers. I can't seem to find any other DIY forum threads that have more detail, pictures or diagrams of one that I could make. If the cost isn't too much I might have a go :) THANKS for your advice.

[NRG]

Is it? Do you have a link to any measurement that show it is? Im pretty sure Apple apply PF correction to their supplies, maybe it's passive and not active and therefore does throw some harmonics back onto the mains but.......it's not DC ;)

[NRG]

http://www.audioasylum.com/forums/pcaudio/messages/14/142108.html

[lurcher]

A Paid of these would do the job. All care as usial with mains voltages etc...

http://www.rapidonline.com/electrical-power/vigortronix-vtx-146-120-112-toroidal-transformer-230v-single-primary-120va-0-12v-88-5201

[Yomanze]

Hmmmmmm, time to dig my balanced mains out and fit a DC blocker on the input, the girlfriend will be happy, not! Very industrial looks.