Isolating Transformer

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Cressy Snr
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Isolating Transformer

Post by Cressy Snr » Fri Aug 03, 2018 4:50 pm

Having bought two 1KVA toroidal isolating transformers off Phil a couple of years ago I decided to make use of the one I had left.

The other one is at our Ant's doing service in his system as a balanced mains unit. The one in the pic below, I configured as a single ended, 0-230:0-230 device:
Image
It powers the turntable, DAC, phono stage and amplifier. Anything with a SMPS, such as the TV, computer, AppleTV and TiVO box is kept firmly on the supply side of the transformer, behind the grounded interwinding screen.

The silent background from the system parts connected to the galvanically isolated secondary side is palpable.
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Cressy Snr
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Re: Isolating Transformer

Post by Cressy Snr » Fri Aug 03, 2018 4:54 pm

It's housed in an IP55 plastic weatherproof box, from Screwfix, and is built to Class II standards.

And yes, the metal screws showing on the top are double insulated, as they go into corner lugs that are moulded into the box in such a way that they are twice removed from the electrical innnards. The toroid is mounted using an M8 nylon bolt, nut and washer.
Last edited by Cressy Snr on Fri Aug 03, 2018 5:12 pm, edited 1 time in total.
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Re: Isolating Transformer

Post by Cressy Snr » Fri Aug 03, 2018 5:09 pm

Mechanical noise from the 1KVA toroid itself is very low, and mechanical transformer noise from the devices on the secondary side, is absent; something I haven't had before, even with the previous BMU.
All this results in a squeaky clean presentation and more access to the music. Nothing to complain about at all. :)
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DSJR
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Re: Isolating Transformer

Post by DSJR » Fri Aug 03, 2018 6:31 pm

Will you be able to compare as it is with say, Ants Balanced output version? Genuine interest as my BMU ain't going anywhere...

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Re: Isolating Transformer

Post by Cressy Snr » Fri Aug 03, 2018 6:38 pm

DSJR wrote:
Fri Aug 03, 2018 6:31 pm
Will you be able to compare as it is with say, Ants Balanced output version? Genuine interest as my BMU ain't going anywhere...
Yes, I'm sure that could be arranged.
Give me a few days.
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simon
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Re: Isolating Transformer

Post by simon » Fri Aug 03, 2018 6:45 pm

Interesting Steve. So what's the difference between yours and Ant's?

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Re: Isolating Transformer

Post by Cressy Snr » Fri Aug 03, 2018 7:02 pm

simon wrote:
Fri Aug 03, 2018 6:45 pm
Interesting Steve. So what's the difference between yours and Ant's?
His is 115-0-115V on the secondary with the centre tap grounded to create the balanced connection. Mine is simply 230V floating on the secondary with no path to earth, so it's wired the same as a building site, or marine safety isolating transformer, which means that none of the devices connected on the secondary side is "live" in the conventional sense.

My old Baird valve wireless with mains transformerless, "live" chassis operation is also plugged into it, so I can't kill myself, or worse, the grandkids kill themselves by poking a metal object through the rear slits. :)
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Re: Isolating Transformer

Post by simon » Fri Aug 03, 2018 10:13 pm

Ah I see!

Yes be interesting how they compare.

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Re: Isolating Transformer

Post by JohnG » Sat Aug 04, 2018 6:21 am

This is of interest to me,
I recently bought a 500va Isolation Transformer to use as a method to control a ground loop.
The ground loop is now controlled by a different method.
Would it be wise to source another 500va tran, and have one for each monoblock power supply.
I intend on having a separate mains supply for the other other devices as they will be on a wall rack about 5-6 metres from the amps and their power supplies.
Or should I run a extended cable mains distribution block for the wall rack from the Iso' Tran's to offer a improved main supply.
Any thoughts on this.

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Re: Isolating Transformer

Post by JohnG » Sat Aug 04, 2018 6:21 am

This is of interest to me,
I recently bought a 500va Isolation Transformer to use as a method to control a ground loop.
The ground loop is now controlled by a different method.
Would it be wise to source another 500va tran, and have one for each monoblock power supply.
I intend on having a separate mains supply for the other other devices as they will be on a wall rack about 5-6 metres from the amps and their power supplies.
Or should I run a extended cable mains distribution block for the wall rack from the Iso' Tran's to offer a improved main supply.
Any thoughts on this.

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Re: Isolating Transformer

Post by RhythMick » Sat Aug 04, 2018 8:32 am

I'm interested in learning more about this.

Your secondary is 230v floating but I assume safety earth passes through?

If so, can the voltage on the secondary drift away from the 0v reference, and does it matter ?

I've used the LL1665 and worked with Jac to build a balanced mains in front of the amp. The secondary centre tap is tied to earth, so the output is +115 & - 115.

Cressy Snr
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Re: Isolating Transformer

Post by Cressy Snr » Sat Aug 04, 2018 8:45 am

I just use a six way socket strip wired to the output of the transformer. It seems to work well.
Accommodating the bulky transformer cases is the main headache when you have a small room, sharing the system with the TV.
I could only get my transformer in place by moving the record cabinet to the opposite chimney breast alcove, swapping it with a small set of drawers.
The 1KVA medical equipment isolation transformers are big, heavy b'stards :)
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Re: Isolating Transformer

Post by Cressy Snr » Sat Aug 04, 2018 9:07 am

RhythMick wrote:
Sat Aug 04, 2018 8:32 am
I'm interested in learning more about this.

Your secondary is 230v floating but I assume safety earth passes through?

If so, can the voltage on the secondary drift away from the 0v reference, and does it matter ?
There isnt any reference to drift away from and the safety earth does not pass through. BBC practice is to remove all earth connections from 13A sockets on the output sides of their isolation transformers.

on the secondary side there is no live and neutral in the conventional sense because the winding is not grounded on one side.
Therefore a case cannot become live, in the case of an earth fault, so no shock if it is touched. This is the thinking behind the "shavers only" sockets in hotel bathrooms.
On the primary side, the safety earth is as it should be and the interwinding screen is grounded to mains earth, so a primary to secondary short will trip the breaker.

Disadvantage of proper isolating transformers, is that if there just happens to be an earth fault in a piece of equipment connected to the isolated side then you won't know, unless you fit a warning lamp so that a faulty piece of gear can be identified by elimination. OTOH that characteristic is exactly why the isolator saves your life in the first place.

Of course if I was daft enough to touch both ends of the secondary, I would be electrocuted.
Last edited by Cressy Snr on Sat Aug 04, 2018 10:18 am, edited 2 times in total.
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RhythMick
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Re: Isolating Transformer

Post by RhythMick » Sat Aug 04, 2018 9:30 am

Interesting thanks. Much to learn as always. What gives a 0v reference for the amps?

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Re: Isolating Transformer

Post by Cressy Snr » Sat Aug 04, 2018 10:05 am

The "0V" is the centre tap of the secondary of the mains transformers within the equipment - the secondary that feeds the rectifier.
This "ground" could be floating 20V above true earth potential, but the amps won't know that. It all depends on what you mean by "ground". It's not actually necessary for "ground" to be earth. Took me a long time to get my head around that one.
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