Mains DC Blocking help

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I suffer from pretty dirty mains and have just bought a couple of BT mains conditioners. An MCU5A/125 and an MCU5A/1000.

They do seem to have sonic benefits, cleaner and a little more dynamic (when plugged in to a different room....read on).

The problem is that they use transformers which hum. The larger unit especially. A little research suggests this is likely down to DC in the mains supply. One possible solution seems to be to use potting compound to seal the transformers into a pot of epoxy like resin. I read that
this can kill transformers over time though. Another solution is to use a DC filter on the mains. This looks preferable. Kind of ironic that I need some sort of mains conditoner for my mains conditioner.

I've unriveted the huge transformer in my MCU5A/1000 and wedged it into place with squash balls. This has reduced (nearly eliminated) case vibration, but it's still too loud.

Any idea where to get good DC filters? Is transformer potting the way ahead? Potting does seem like curing the symptom and not the illness, so I'd rather sort the DC issue out at source.

 

[Anonymous]

Need more details of your site.

Is the 'true earth' fresh with new connections at both the meter and consumer unit?

Has the cross bonding been checked and cleaned?

What else is plugged into the 20A ring main?

What is the voltage readings off the Neutral/Earth lines before and after the above?

What in the house is generating so much contamination and where is it situated on the bus bar in the consumer unit?

Get back to me with some info and I see if I can help you.

 

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The house is a shared rent student stylee. Wiring probably done about 15 years ago by the landlords cousin or some cowboy judging from the crazy location of some of our light switches.

I live close to the city centre (3 minutes walk), but have no obvious heavy industry nearby.

The true earth at meter will be pretty groady tbh. I haven't actually looked, but I doubt anybody has given it a polish and deoxited it or whatever the recommended procedure is since installation.

Crossbonding will be similarly untouched (I'll have to do a Google search to even figure why we need cross bonding, but hey I'm learning new stuff all the time).

I'm obviously going to have to do some internet research on UK domestic mains wiring and go venture into the cellar to see what I can see. As I said, I'm learning something new all the time. Sorry if I'm not much help on the current (forgive the pun) state of the house wiring. It's always been the landlords problem. Trouble is, even if I identify obvious problems my landlord won't resolve them just to make my HiFi sound better. I'm going to need to spot something lethal or a voltage far enough out of UK standards that the electricity supplier has to fix it if I'm going to see any work done.

I seem to get switching noises from 2 fridges and freezer and possibly central heating/water boiler.

Downstairs there's also a couple of bedrooms with usual PC,TV,DVD, minisystem and similarly equipped front room.

I don't have a meter to see what my mains voltage is but am coming to the conclusion it might be more useful than an SPL meter. Any recommendations for a cheapish one?

In the room with the hifi there's the following:-

Items in my sig plus a kettle seeing frequent action (music never loud if kettle is on).
The rest of my kit hasn't been switched on or even plugged in for the time that I've had the BT unit except for brief TV and CD testing to see if there's any improvement. when the dust settles my other kit will get plugged in again and consists of CD, DVD, FView, DAB, TV, AV amp, seperate power amps for each of 4 surround channels, 2nd PC. I also have other odds and sods, battery charger, MP3 charger, phone charger, wall light etc.

The room has 2 double wall sockets. A block for power amps and an 8 way Brennestuhl aluline block (for PC, monitor, DAC, Pre and SubEQ) share one double wall socket. The second double wall socket has TV and subs into another Brennestuhl 8 way and kettle directly to wall.

All mains cables are bog standard at present but I have some basic shielded cables already ordered. Half metre or as short as I can get away with elsewhere. My plugs went to the jeweller's/silversmith on Saturday and I hope to have cables by Friday. I won't be able to press them all into service until I get some male IEC's to replace cables on units which use a captive lead.

As for the tranny it's an EI type. My research has been suggesting that torroidal transformers can hum due to DC infecting the AC, but EI types don't suffer from this. EI types are just prone to humming anyway it seems. This may make my DC filter idea redundant anyway.
That said I do have torroidals in the power amps which hum, suggesting there is a element of DC to contend with. Power amp torroid hum is nothing compared to this EI transformer hum in the BT unit though. The BT 1000 is loud. The BT 125 isn't nearly so bad. I also noticed the other day that my Beresford ACDC adapter sounds like it's got an angry wasp inside it. You have to listen closely but Stan definitely put a wasp in there.

I have found a 3A DC blocker from DIYHiFI Supply and another 3A from ?somebody else? but these appear too small, I really would like 5A to run power amps and subs. It seems there's a few circuits floating round the DIY circuit. I don't have the smarts or finesse in the fingers to either judge which are the better designs or to build my owm, no matter how simple they look on paper.

I'm planning on presenting it to BAWCO (Bradford Armature Winding Company) tomorrow to see what they have to say. I think a rewind will be prohibitivelty expensive but they might tell me whether potting or DC filters might work.

Even with the effort and heartache to get it right, I still think it'll work out cheaper than an audiophile unit. I'll sure as hell know more about what is going on than just spending hundreds on a simple plug and play solution.

Any input you can gve would be most appreciated. Maybe start me off with the best links for house wiring.

Cheers and thanks for reading this far.

 

[Anonymous]

Oh boy, where do I start!

Out of curiosity where do you live, Leeds/Bradford?
I live in Leeds.

By what you write your Mains is filthy.

Ist off here are a few sites to read up on...

http://www.dself.dsl.pipex.com/ampins/groundloops/grndloop.htm

http://www.russandrews.com/viewindex.asp?lookup=1&region=UK&currency=GBP&article_id=pg

and one on filters...http://www.diyhi-fi.co.uk/html/mains_filters.html

By what you write it appears you have a seriously overloaded 20A ring main as well with what you have plugged into it!
The things you can do is ensure that each plug socket is earthed to the casing, check that it is a 20A breaker in the consumer unit.
You will never get the performance out of your system in the present circumstances, but you can get improvements dealing with the noise floor which is very high. Put 13A fuses in the BT units and try grounding the cases. (there is an earthing point on them)

Lets do one step at a time and make some steady progress.

 

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Thanks for the reply Trevor.
As this thread has received so few hits and looks to have turned into me consulting you (Trevor) on specifics I've added my EMail address to my user info. I'll leave it there for a week or so. You can reach me that way or continue to post here. Whichever you feel is best.

if you could indicate which of the ideas below are wrongheaded or suggest a better path to take that would be great.

Yes I'm in Bradford. I didn't make it down to BAWCO though.

I've read those links, cheers. Actually I'd read the first before after you linked it in another thread. I'd also already read some of Russ Andrews articles. I've gone back and read them all now.

I have a few queries.

Should I switch off power at consumer unit first? It seems unesessary as earth to gas and water pipes are before the consumer unit. If I'm just sliding connection along water pipe to clean, everything should still be earthed at gas pipe. Also, Russ doesn't mention switching power off for this as he does in other places. However, for 100% idiot proofing would you advise it?

You suggest replacing plug fuses in BT units for 13A. The big boy (the MCU1000) has no internal fuses, and is fitted with a 10A in the plug socket. Would you advise changing this to a 13A too? Though it doesn't indicate correct fuse size I figure that's probably right as I'd expect an amateur to put a 5 or 13A in as they are more common than 10A.

Re component case earthing. The only convenient earth point besides my wall plug socket earths is a stainless steel gas pipe. What would be prederable, earthing to this or to mains earth?

What do you think of this as an idea for a near star earthing point for component cases. Wilmslow Audio subwoofer high level subwoofer terminal plate. Looks like a cheaper alternative to Russ Andrews £100 jobbie to me.
https://secure.wilmslow-audio.co.uk/catalog/product_info.php?cPath=26_44&products_id=270

Should I make up a cable with a banana plug on one end and MK toughplug on the other wired to earth with earth wire? I could plug this into the wall with a little box type 2 or 3 way block shared with either power amps or kettle

How inflexible is 6mm earthing cable for case earthing? I assume that it would give me lower impedamce than 4mm cable and the wire could be spaded or banana plugged as 6mm includes sheathing.

Could I take

I was thinking of getting Supra Lo Rad to rewire my 8 way blocks at some point. Are there better options foe less? A little over £12 metre for 2.5mm if my memory serves me correctly.

I found the page about experimenting with reverse wiring transformer primary windings interesting. It hadn't occured to me before that Fig 8 cables are symmetrical sockets so the N and L could go in either way. It's obvious when you stop and think.
As a time saving exercise, rather than conduct listening tests on each piece, would it be quicker to hand test the level of magnetic attraction with say a screw held above the transformer with power applied? I thought of that as a lazy shortcut. It could save me having to do listening tests on a myriad different components if it would work.

Whilst on transformer interference. Would there be any mileage in lining the underside of my equipment shelves with a few layers of aluminum foil taped down with gaffa to prevent tearing and interconnect shorting? Would that reduce any interference between components on adjacant shelves? I'm thinking outside the box here.I'm inclined to worry about filtering when the rest is in place. I think solid basic wiring is the first thing. Then see how the BT hum is going. If it's still present I'll have to try to establish cause.

Right, shopping list
Deoxit, possibly a 20A breaker for consumer unit (need to look and also suss which one feeds the system).
Plug fuses (I need to stock up anyway as I'm having to plunder them from surplus cables at moment).
Banana plug plate from Wilmslow Audio, bit of wood and felt to mount it on, maybe more banana plugs and/or spades (need to check my spares box), bunch of earth cable, toughplug.
Kitchen foil (got that already), gaffa tape.
Supra Lo Rad for 8 way blocks (eventually).
Male IECs for captive components.

Sorry, this post got a bit long and rambling. Well, it's too long to edit down now, so it'll have to stand.