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Mains isolation - would this work?

This is probably the wrong place to post this, so mods feel free if it fits better somewhere else.

I was at a hifi show last weekend. Most of the rooms had some kind of mains filtering etc, but one guy had some big transformers. They were what we call site transformers and they step the voltage down from 240V to 110V which is what tools on a building site are meant to be by regulation here.

So the guy has 2 of these wired back to back, ie the 110V out of one connected to the 110 out of the other and then using the transformed 240 out for powering his amps etc. (240mains>>110V out>>110Vin>>240V out)

These were each 5KVA rated. The guy reckoned they did all that a £2k isotech mains unit did.

What do you guys think? Worth pursuing?

Fran
 

gareth

Member
2008-01-31 3:38 pm
woodturner-fran said:
This is probably the wrong place to post this, so mods feel free if it fits better somewhere else.

I was at a hifi show last weekend. Most of the rooms had some kind of mains filtering etc, but one guy had some big transformers. They were what we call site transformers and they step the voltage down from 240V to 110V which is what tools on a building site are meant to be by regulation here.

So the guy has 2 of these wired back to back, ie the 110V out of one connected to the 110 out of the other and then using the transformed 240 out for powering his amps etc. (240mains>>110V out>>110Vin>>240V out)

These were each 5KVA rated. The guy reckoned they did all that a �2k isotech mains unit did.

What do you guys think? Worth pursuing?

Fran


Personally, two quite large bright yellow transformers sitting in the living room with my equipment and generating large magnetic fields..! It's up to you. Not to mention power factor.

If you look in Farnell's they offer iec inlet filters which you can retrofit to pretty much anything. They are made by Schaffner, come invarious types and ratings and will probably offer similar results. More importantly they filter each device as is needed. Have a look and if you are a little unsure then let me know.

Gareth
 

bob_v5

Member
2005-09-04 5:38 pm
"I suppose if there was DC on the mains it would be gone, but other than that?"
I'm sure that the mains transfo in the amp would also get rid of any DC on the mains. Unless my electronics teacher is lying to me, transformers simply do not pass dc.
I agree with Gareth, buy the filters he talked about, and spend whats left on something more exciting.

edit-- I typed my reply too slow!
 
Hi,
I'm led to believe that the DC in the mains signal is not pure DC nor is it an offset in the zero volt line towards one or other of the voltages.
I believe that the DC, that affects toroids particularly, is the unsymmetrical waveform that creates a net unbalance between the +ve and -ve halves of the distorted mains supply waveform.
The EI transformers that are being suggested will in themselves be fairly resistant to the saturation from the net DC, but are quite good at passing the distorted waveform on to the next stage of the audio equipment.
That's a round about way of saying that a pair of back to back transformers does not block DC.

Look for the balanced mains threads and websites.
The back to back transformers being discussed in there are being used as part of a filter system to remove much of the interference and some of the waveform distortion. These transformers can also be used to create a balanced supply to the audio equipment, the advantage being that leakage from the mains transformer in the audio equipment is balanced and gives a cancellation in the currents flowing to ground. Those that promote this type of filtering claim significant audio advantage.
I think it's Rane or Jensen that have a paper showing the tech side of this ground current cancellation.
 

gareth

Member
2008-01-31 3:38 pm
In therory whatever is on the primary side of a transformer, through electromagnetic induction, will appear on the secondary side of the transformer. Let's not forget that the real reason we have isolating transformers is safety.

I am not saying that they don't work but I am dubious as to the benfits. Companies like Is0-Tek are manufacturing big, heavy and shiny boxes which, I would imagine, have a lot of appeal. Not to mention can cost thousands of pounds.

EMI/RFI filters work on a similar basis as any other filter, e.g. speaker crossover, in that they present a reactance with rising frequency then the impedance 'kicks in'. Again there are many fields of belief in this area, if you like the sound then it is good, no?

I have carefully chosen Schaffner filters fitted in some equipment at home, CD63se etc, and find the effect quite pleasing. Noise floor seems to have reduced, slighly better seperation of instruments and a more pleasing soundstage. Before anyone disagrees, you can if you want, let me say that Marantz have provided for common-mode rejection already on the circuit for the CD63se and they know a lot more than I do.

Anyway if you want to try mains isolation without re-mortgaging or turning your house into a building site then if you have a shaver outlet at home, the one with the two pin outlet in 240/120 volt @ 2amp then give this a try. This is a double-wound isolating transformer and although it may only give out around 480 watts of power the transformer is the same. Don't try plugging in your Mark Levinson monoblocks here though! You may have some extra central heating or even a free fireworks display.

Personally, being an electrician, I feel that cleaning the power supply is theoretically worthwhile especially when you understand how all our house are connected. In fact I think I am starting to become a little obsessive with this as the results can be surprising.
Remember how when someone was about to ring on your mobile phone and if your TV was switched on you would get a forewarning.

Anyway I hope you enjoy finding what works best for yourself.
Gareth
 
This is an interesting discussion!


Look, the truth be told, I'm not that big a believer in this myself, but my ears would be open to persuasion. All I know is that the guy at the demo rated it highly - "as good as a £2k mains unit" were his words. Allowing for a bit of loose speak etc, you could still say he thinks it has a good effect. And this was in a hotel environment where its always reported how bad the mains supply is.

Anyway, I thought it might be something worth trying if you had handy access to 2 of these things, but not worth spending the money on right off.

So from the posts so far, it hasn't found much favour here - and I understand that. A friend who was with me was since speaking to someone who is an engineer for a company who installs UPS and stabilised supplies for specialist equipment and he more or less rubbished it too. He said he did have another thing that he could get, but would cost about 500-600 euro. He is to speak to him again to find out exactly what it is.


On the jkeny link: yes, we have been talking but I think he wants it for the step down only and any clean up would be a side benefit. Jump in jkeny if I have that wrong!


Fran
 

gareth

Member
2008-01-31 3:38 pm
Right, I am going to give this a try. I have two 240-110volt transformers here and I think I should test this to satisfy my own inquisitive nature. These have been lying around my home for ages and to be honest I have never really thought about doing this.

First, I am going to remove the iec inlet filters in my equipment and put the non-filtered back in and then to some listening.

Gareth
 

gareth

Member
2008-01-31 3:38 pm
woodturner-fran said:
Great stuff Gareth,

I only have one and was looking to get a lend of another to try it out. Let us know how it goes!


Fran


Will do Fran, by the way do you have B&Q or some other diy outlet over there? You can pick one of these up for about 70 euros. Although it may be a waste of money for you. Have you got a shaver outlet ?

Gareth
 

jkeny

Banned
2007-02-06 12:43 am
Dublin
Hey Fran,
As you can see I posted this over on PS section - yes you're correct, I'm looking at it for step down uses but I want to check/maximise any other benefits.

As you know I have a 230V UPS which I may be able to modify to output 130V & this may clean PS more but so far the postings on this over at PS are negative too!

I'm hugely interested in the experiment outcome - keep us informed!