Sjostrom DC Blocker

[killie99]

Recently I've stated getting hum from the transformer in my amp. It would come and go, sometimes loud, sometimes quiet and sometimes silent.

After a bit of googling I decided to try a DC blocker and came across a rather nice bare PCB from Sjostrom Audio. They also sell a populated version but it's hardly a difficult thing to build - 4 connectors, 2 diodes and 2 caps.

PCB duly ordered and parts purchased to let me house it in as small a plastic box as I could find (120mm x 95mm x 35mm). Took about an hour to make and it looks like it has done the trick, no more humming transformer!

Total price was around £35.

http://stuartlittlejohn.f2s.com/dc_block1.jpg

http://stuartlittlejohn.f2s.com/dc_block2.jpg

[walpurgis]

That looks a handy gizmo.

[Bigman80]

Has it worked?

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[Barry]

:rolleyes:


Has it worked?

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Took about an hour to make and it looks like it has done the trick, no more humming transformer!

[Bigman80]

Ah lol, [emoji38]🤤

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[killie99]

yes, it works a treat. Very simple and very effective.

[sq225917]

I have a pair of them, very handy.

[RobbieGong]

Got one of these too :) - DC blocker or dc trap as they are known.

'Quote' - With modern appliances all over the place doing strange things to the mains waveform (especially hair-dryers on half power and the like) you can end up with a DC component on what should be a pure AC voltage. Doesn’t even have to be in your house – could be your neighbour or somebody three doors away!

Large toroidal transformers like the daddies in my Sansui AU-919) don’t like DC voltages, so they complain by growling or humming.......

[Gazjam]

Interesting...

Started powering my 300B SET amp from the Balanced Mains Unit and theres a bit of intermittant buzzing on the transformer?
Its in the next room out of earshot so not annoying, but be good to eliminate it in case the DC is affecting sound quality.

A good shout, and not too spendy, be picking one up.
Thanks for posting Stuart. :)

[Bigman80]

Could one of these be placed at the front of a multi plug ?

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[walpurgis]

Could one of these be placed at the front of a multi plug ?

I don't see why not. As long as it can handle current up to and somewhat over 13 amps.

[DiveDeepDog]

Could one of these be placed at the front of a multi plug ?

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Good point, I've got mono blocks, would the collective advise 2, or would 1 prior to block work?

[Bigman80]

I don't see why not. As long as it can handle current up to and somewhat over 13 amps.How would one ascertain that information, Geoff?

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[killie99]

If any equipment on the multiplug is causing a problem then placing the blocker before the multiplug wouldn't work but I think it's very unlikely unless you're plugging in something like a hairdryer!

Think I'd buy more than 1 rather than using it with a multiplug. I reckon if you buy all the bits at the same time you could probably make 2 for £50.

[Bigman80]

Well, my thinking was that if everything on the mains is causing "interference" then a DC blocker on the multi plug I use, just for the HIFI equipment, might help all of it. Just a thought and I'm completely unqualified to know but I thought it made sense.

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[killie99]

The blocker is specifically to reduce transformer hum so 2 mono blocks plugged in to the multiplug shouldn't be a problem (assuming the mono blocks have transformers). The blocker should have no effect on anything else.

[sq225917]

The amount of dc they can mop up is limited by the number of diodes on the pcb, more diodes, more dc mopped up. If I recall correctly it's just over half a volt per diode. I have all six fitted on mine.

[Bigman80]

I will do more digging. Thanks for posting about this !!!

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[Simon_LDT]

I have been using one on my monoblocks for over a year now. Does a good job, there is only a whisper of a hum now if you place your ear near the amps. Before, they were generally quiet but at certain times during the day/week they would go batshit crazy with hum - not anymore.

I wired mine using 1 blocker and jammed 2 sets of cable into the output plug, which tails off into 2x IEC sockets, one for each amp. I've now picked up a 2nd blocker which I will likely use in the extension block for everything else - got it mainly for my LPS which also can hum loud at times.

Got mine from a guy named Alex here: http://www.atlhifi.com/

Does all kinds of combinations and can also supply just the boards or a fully built one in a case.

[Bigman80]

I have been using one on my monoblocks for over a year now. Does a good job, there is only a whisper of a hum now if you place your ear near the amps. Before, they were generally quiet but at certain times during the day/week they would go batshit crazy with hum - not anymore.

I wired mine using 1 blocker and jammed 2 sets of cable into the output plug, which tails off into 2x IEC sockets, one for each amp. I've now picked up a 2nd blocker which I will likely use in the extension block for everything else - got it mainly for my LPS which also can hum loud at times.

Got mine from a guy named Alex here: http://www.atlhifi.com/

Does all kinds of combinations and can also supply just the boards or a fully built one in a case.[emoji106]

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[Floyddroid]

[emoji106]

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I would like one of these devices already made up in a box. I don't know why designers and manufactures don't offer an option of buying LPS's with dc blockers fitted.

[Bigman80]

I would like one of these devices already made up in a box. I don't know why designers and manufactures don't offer an option of buying LPS's with dc blockers fitted.Gap in the market?

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[Floyddroid]

Indeed.
Gap in the market?

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[killie99]

The prebuilt one from atlhifi looks pretty decent but it's a lot of money for something so simple.

[Floyddroid]

75 Euro i believe Stuart.
The prebuilt one from atlhifi looks pretty decent but it's a lot of money for something so simple.

[Yomanze]

Interesting, especially as it's from a real engineer, and a great price.

...if you opened up those multi £100 boxes that you can find from some retailers, this is pretty much what you'll find inside.

[sq225917]

You couldn't build and box the sjostrom one for 75 euros. Not unless you like real ugly boxes.

[Bigman80]

The prebuilt one from atlhifi looks pretty decent but it's a lot of money for something so simple.I'm building one of these. Still awaiting Diodes!!!! Doh. My fault. Ordered from china

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[sq225917]

Wtf would you order any parts from China?

Rule number one of diy, only buy from known good sources.

[Bigman80]

Wtf would you order any parts from China?

Rule number one of diy, only buy from known good sources.

Yes, I hadn't realised, Simon. It was quite late and i didnt pay enough attention to the listing. Lesson learned. Saying that, i have had no issues previously with Chinese sellers.

[Yomanze]

Some Hong Kong sellers are amazing though...

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[sq225917]

Farnell, Mouser, rs or little diode for parts. Other than that stick to single item specialists, ie a guy who only does Toshiba jfets.

[Yomanze]

Farnell, Mouser, rs or little diode for parts. Other than that stick to single item specialists, ie a guy who only does Toshiba jfets.

Agreed, although Little Diode is rather expensive. I would add Cricklewood for rare / obsolete parts. :)

[Bigman80]

Well, the Chinese diodes arrived today and seem to be fine.

All the soldering is finished and it's in the power line to the Amplifier and phonostage.

I used an old plastic box I'd bought for another project a while back. The capacitors were a bit to big so I've improvised lol.

It'll be out of sight so shouldn't matter. I will swap the box at some point. Thanks to the OP for the idea to build one of these. As my first ever project it went well.

https://uploads.tapatalk-cdn.com/20170830/03dee8d190488c1be55951c5efefbcca.jpghttps://uploads.tapatalk-cdn.com/20170830/34f6ed74317bc7af02b62a2097e00c90.jpghttps://uploads.tapatalk-cdn.com/20170830/fc62b129548efcb8b2846c05b7770a6d.jpg

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[Yomanze]

My DC blocker PCB has arrived from Sjostrom audio. Looking forward to building this. I get both constant and intermittent transformer hum due to DC, which caused my now-sold balanced mains unit to buzz rather audibly (was pretty much silent in my old house). All parts including the case are totting up to around £65. Am using the same parts as the design, with a polycarbonate case & a couple of LAPP cable glands, and a ferrite clamp on the output lead. Due to ease more than anything else, will be wiring it using Supra LoRad 2.5.

https://sjostromaudio.net/cart/298-large_default/dct03-dc-filter-for-toroidal-transformers-heavy-duty-built-unit.jpg

[Bigman80]

My DC blocker PCB has arrived from Sjostrom audio. Looking forward to building this. I get both constant and intermittent transformer hum due to DC, which caused my now-sold balanced mains unit to buzz rather audibly (was pretty much silent in my old house). All parts including the case are totting up to around £65. Am using the same parts as the design, with a polycarbonate case & a couple of LAPP cable glands, and a ferrite clamp on the output lead. Due to ease more than anything else, will be wiring it using Supra LoRad 2.5.

https://sjostromaudio.net/cart/298-large_default/dct03-dc-filter-for-toroidal-transformers-heavy-duty-built-unit.jpgWhat case have you gone for?

[Yomanze]

What case have you gone for?

Nothing fancy, just this: https://uk.farnell.com/multicomp/g2113/box-polycarbonate-240x120x60mm/dp/1526668

[Bigman80]

That's all it needs!! Good luck with this, I'll be watching [emoji6]
Nothing fancy, just this: https://uk.farnell.com/multicomp/g2113/box-polycarbonate-240x120x60mm/dp/1526668

[Yomanze]

That's all it needs!! Good luck with this, I'll be watching [emoji6]

Cheers. :) Ah that was the wrong link, I need a bit more height for the box, but will be similar.

[Bigman80]

Cheers. :) Ah that was the wrong link, I need a bit more height for the box, but will be similar.Ha!! As long as you haven't ordered the wrong one [emoji4]

[Yomanze]

Ha!! As long as you haven't ordered the wrong one [emoji4]

Nope ha ha, it's this one! https://uk.farnell.com/multicomp/g2018/box-polycarbonate-240x160x90mm/dp/1526678

[Bigman80]

Putting a socket on the top?
Nope ha ha, it's this one! https://uk.farnell.com/multicomp/g2018/box-polycarbonate-240x160x90mm/dp/1526678

[Yomanze]

Putting a socket on the top?

Cable glands on each end. One will be hardwired into my mains block, the other side will have a plug on it.

https://uk.farnell.com/lapp-kabel/53111020/cable-gland-pa-13mm-m20-grey/dp/1178870

https://uk.farnell.com/lapp-kabel/53119020/locknut-pa-6mm-m20-grey/dp/1178912

[Bigman80]

Cable glands on each end. One will be hardwired into my mains block, the other side will have a plug on it.

https://uk.farnell.com/lapp-kabel/53111020/cable-gland-pa-13mm-m20-grey/dp/1178870

https://uk.farnell.com/lapp-kabel/53119020/locknut-pa-6mm-m20-grey/dp/1178912Excellent. I like it.

[sq225917]

We've all still got a way to go to catch up with Marks'.

https://pinkfishmedia.net/forum/proxy.php?image=http%3A%2F%2Fi62.photobucket.com%2 Falbums%2Fh90%2Fmarkemark_2006%2FDC%2520Blocker%2F A640608D-952B-4666-BEB0-166AF2206FA3_zpstkoscmkw.jpg&hash=1acb909c62eeb6c81535c5d1a1f803cb

Mine doesn't even have a box

[YNWaN]

Yeah, I built one of the large D.C. blockers mentioned and am really pleased with the results. I did try the smaller one also described in this thread but it didn’t quieten my transformers at all and, if anything, actually impaired sound quality.

http://i62.photobucket.com/albums/h90/markemark_2006/DC%20Blocker/3AD66962-E366-4108-9400-4AAED1B2D5E0_zpscu7zyymx.jpg (http://s62.photobucket.com/user/markemark_2006/media/DC%20Blocker/3AD66962-E366-4108-9400-4AAED1B2D5E0_zpscu7zyymx.jpg.html)

[Yomanze]

Looks cool Mark, take it you used the plug socket for your Hydra?

[YNWaN]

Yes, that's right Neil - hence the Cerberus name, to keep the theme with the Hydra :). pretty much my whole system is run from it.

[Yomanze]

Yes, that's right Neil - hence the Cerberus name, to keep the theme with the Hydra :). pretty much my whole system is run from it.

That's encouraging RE running your whole system from it, because I intend to do the same. :)

Have been looking into a hydra too, but don't want to compare 2x fundamental changes at the same time, so will try the DC blocker first, then look at a Grahams hydra to replace the mains block & cables.

[Yomanze]

Putting a socket on the top?

Hi Oli, I was planning the layout & you're right, it's better to put the glands on the top lid, at one side to keep the internal cabling short, easier to drill too. :)

[YNWaN]

That's encouraging RE running your whole system from it, because I intend to do the same. :)

Have been looking into a hydra too, but don't want to compare 2x fundamental changes at the same time, so will try the DC blocker first, then look at a Grahams hydra to replace the mains block & cables.

Yeah, I’ve got three power amps going through it, four if you include the one in my sub. There are three 500VA transformers too.

The Hydra is also well worth doing. Second hand Graham’s ones come up quite regularly and that is what I would have likely bought if I wasn’t so into making my own stuff.

[Bigman80]

Hi Oli, I was planning the layout & you're right, it's better to put the glands on the top lid, at one side to keep the internal cabling short, easier to drill too. :)[emoji4].

Good move.

[Yomanze]

BOM was more expensive than I anticipated, £80. Have used the same parts as the Sjostrom unit, those caps are over a fiver each. Still, the price pales into insignificance when looking at other sellers, where the price can hit £250 fast, more for high current units, and for what?!

[Bigman80]

BOM was more expensive than I anticipated, £80. Have used the same parts as the Sjostrom unit, those caps are over a fiver each. Still, the price pales into insignificance when looking at other sellers, where the price can hit £250 fast, more for high current units, and for what?!There are higher priced ones too. This is still a good price.

[killie99]

I built a 3 output version of the bigger DC blocker unit:


https://i.postimg.cc/Y9VmhtFn/dc-3.jpg

https://i.postimg.cc/Ls9PWCRT/dc-2.jpg

https://i.postimg.cc/NGzxHcYw/dc-1.jpg

[Yomanze]

^^ Looks great! Nice and neat.

How has it been in your system Stuart? :)

[killie99]

I use it quieten down the linear power supplies I use for powering 2 pi's, network switch and linear power supply for my phono stage. No more buzzing! Don't think it makes any difference to how the hifi sounds, just stops the annoying buzz.

[Yomanze]

I use it quieten down the linear power supplies I use for powering 2 pi's, network switch and linear power supply for my phono stage. No more buzzing! Don't think it makes any difference to how the hifi sounds, just stops the annoying buzz.

The annoying, often intermittent buzz is very* audible in my home. Usually I get a sonic penalty from trying filtering or isolating / balanced mains arrangements, so hoping this does indeed drop the buzz down without the bad bits. :D

* Depending on how much you're listening to it.

[YNWaN]

Both I and a friend thought it did actually improve the sound, as well as reducing/eliminating transformer hum.

Very neat build Stuart :thumbsup:. I didn’t bother using the board return, or ground connections, though as these are just through connection points and cary no signal from the circuit. I wired the ground and return directly from the input to the output socket. Only the + actually passes through the board.

[Yomanze]

Just got back home from London, and my parts got delivered to work in Manchester. I haven’t felt like a kid waiting for some toys in a while.

[Mand]

Came across this thread last night, then my power amp was buzzing much louder than normal afterwards.
Been quiter this morning. Nevertheless I've ordered a built dc blocker from atl audio.
Hope it works as intended.

[YNWaN]

Hmm.. it might do. However, when I tried one the size of the ATL unit it didn’t do anything and a much larger design was needed.

[Firebottle]

I built a 3 output version of the bigger DC blocker unit:


https://i.postimg.cc/Y9VmhtFn/dc-3.jpg

https://i.postimg.cc/Ls9PWCRT/dc-2.jpg

https://i.postimg.cc/NGzxHcYw/dc-1.jpg

Put an earth connection to the case for full safety.

[killie99]

There is already, you just can't see where it's attached in that picture - it's to the right of the live out on the board (but you can see the case ground wire coming out the earth connection)

[Mand]

My ATL blocker came from Bulgaria about a week after ordering. Well made, weighty unit.
Works very well. Today I only had low level hum but once installed I have none..
So I'm glad I happened across this thread, thanks guys.

[sq225917]

Killie, check case continuity to each panel, the last paradise I built needed some anodizing scraping off, same modushop case.

[BilliumB]

Any idea how many volts of dc the Sjostrom unit blocks?

Cheers. Bill

[sq225917]

Up to 8v

[killie99]

Killie, check case continuity to each panel, the last paradise I built needed some anodizing scraping off, same modushop case.

You are correct, had that with every Modushop case I've used as well. Continuity was checked to all panels but well worth mentioning in case anyone else uses Modushop cases.

[Ammonite Audio]

The same applies to any anodised alloy case irrespective of maker - the anodised finish in non-conductive so you need to ensure that any earth points go to clean metal.

[peranders]

Any idea how many volts of dc the Sjostrom unit blocks?

Cheers. Bill
It will remove 4 diode voltages, so around 2-4 volts depending of load. It seems that only one diode will do the trick in most cases.

[sq225917]

I have a six diode and 16 version here, the difference is significant.

[YNWaN]

It will remove 4 diode voltages, so around 2-4 volts depending of load. It seems that only one diode will do the trick in most cases.

In some cases perhaps, but certainly not in all cases and particularly not in mine, or my friends. Given the, relatively minor, price diffference I very strongly recommend the larger D.C. trap as this works very much better, profoundly so, in fact - highly recommended.

[sq225917]

Yeh, chalk and cheese here.

Welcome to the forum PerAnders, (for it is he, the man himself).

[BilliumB]

It will remove 4 diode voltages, so around 2-4 volts depending of load. It seems that only one diode will do the trick in most cases.
Thanks for that - I've been looking for a dc blocker that deals with higher levels of dc.

Cheers. Bill

[sq225917]

Bill, this will do for you. If you have more than 4v on your mains that's a job for the supplier to fix.