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EI Vs Toroidal transformers
EI Vs Toroidal transformers
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Old 12th June 2003, 06:45 AM   #11
Peter Daniel is offline Peter Daniel  Canada
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I was also biased to use EI as I was told that they are superior to toroids. So was for a big surprised when I built powr supply for my GC using two 200VA EI transformer with split bobbuns (one transformer per rail). It sounded worse than a PS using a single, 400VA Plitron toroid, everything else being equal. So now I will be listening firs before deciding on a transformer.
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Old 12th June 2003, 08:18 AM   #12
jh6you is offline jh6you
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Default Can't argue with subjective posts:)

Quote:
Originally posted by walker

... have you been able to evaluate the same amp designs with different transformers?
Yes, mine is very subjective feeling.

I still have these two at home:
  • Zen with EI transformer made by a tube lover.
  • Zen with Ulveco toroidal transformer.
Of course, both work fine.

JH
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Old 12th June 2003, 09:40 AM   #13
djk is offline djk
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"A Faraday shield, (electrostatic shield), easily takes care of Capacitive coupling between primary and secondary windings."

Garbage repeated endlessly is still garbage.

A split-bobbin EI transformer has less capacitance than a toroid with an electrostatic shield.

I own a capacitance meter, do you?

"I still think that toroids are better transformers, all be it at a higher price, but I've been wrong before, and will be again"

In small quantities toroids cost less than EI types, one reason why they are popular.

"AC supply filtering isn't a black art, though at times it appears to be"

Maybe you should apply for the job of designing them. Most off-the-shelf line filters INCREASE the noise.

I have had people want to return power amps with toroids because of mechanical 'buzz' from the transfomer. I don't get that with EI types.

Put these on toroids all the time, never used one yet on an EI transformer:

http://www.hifi-notes.com/images/offsetkiller300i1.jpg
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Old 12th June 2003, 04:55 PM   #14
Jocko Homo is offline Jocko Homo  United States
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Default Not sure I should touch this one.........

In brief, let's say in transformers, you only get what you pay for. I have many good and bad examples of either style.

I use both, and I can not give an easy, all-encompassing rule as to which and when. Sorry, it is not that easy. Sometimes factors other than performance dictate which is used. The trick is then to make whatever you end up with work.

I know........no help at all............

Jocko
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Old 12th June 2003, 05:21 PM   #15
tiroth is offline tiroth  United States
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I have some little split-bobbin semi-toroidal transformers that I use for line-level/digital applications. Primary:secondary Cp is only 6pF! Try that with a toroidal.
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Old 12th June 2003, 05:26 PM   #16
dhaen is offline dhaen  Europe
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Normal toroids rarely have electrostatic shields, so pass common mode noise. This may not affect the power amp, but can be transmitted to the preamp, where the levels are lower, and hence more susceptable.

Cheers,
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Old 12th June 2003, 05:55 PM   #17
tbla is offline tbla
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Wink well, ich bin ein frankfurter....ei rules...

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Old 13th June 2003, 02:08 AM   #18
walker is offline walker  Australia
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Djk, read your post with much mirth, cheers.

Lets not forget that the amount of capacitance isn't the important issue, its ability to pass noise through electrostatic coupling from primary to secondary windings seems to be the concern. With a faraday shield there is a lot of capacitance from primary to the shield and much the same between the secondary and shield. If the shield is connected to a quiet enough ground, then dV/dt (electrostatic) garbage in, garbage goes to ground. The secondary is electrostatically connected to ground not the primary. Please correct me if Iíve missed the point you were trying to make. Garbage in garbage out, is a little vague.
I still believe that "A Faraday shield, (electrostatic shield), easily takes care of Capacitive coupling between primary and secondary windings."

Djk, youíre not the first to buy an off the shelf filter and expected of it, what it wasnít designed to do, been there myself in the murky past.

Regarding magnetostriction noise. Iím not even going to try to guess how many noisy transformers that Iíve come across or had to silence, but itís got to be 3 figures at least. The majority of transformers are EI so it would be hard for me to accurately gauge which where more prone the magnetostriction noise. I have a humming EI here at the moment that I have to deal with, Iíll try the usual fixes and replace it if they donít work. One common denominator with noisy transformers that I have noticed is the cheap ones tend to be the culprit more often, funny that.

Djk, I also have been able to buy toroids in the past occasionally cheaper than EI but they were I suspect surplus stock. If cost is the main driver here I think we all know the winner

The offset killer? A MOV? That wonít kill the offset, it will clip the waveform, the offset remains, but youíve got to love the marketing

Dhaen, you are right in my experience, toroids with faraday shields are the exception and more costly, in fact EIs with shields are also a rare breed. Iíve only found them where noise is an issue that the manufacturer is prepared to deal with. If low cost and availability were a key issue then EIs without shields would be the obvious choice in most cases.

Tbla, I wish I could read Danish? So youíve got me at a disadvantage, would you like to summarise the article?

Enjoy the music, take care, regards WALKER

Oh, and capacitance meters, yes I do own a few, 3 last count, but that doesn't mean I know anything other than where to but them
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Old 13th June 2003, 03:50 PM   #19
mlloyd1 is offline mlloyd1  United States
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EI Vs Toroidal transformers
I'm confused
Are you saying the big cap(s) in series with the transformer primary cannot or do not block DC from reaching the transformer?

mlloyd1

[QUOTE]Originally posted by walker
....
The offset killer? A MOV? That wonít kill the offset, it will clip the waveform, the offset remains, but youíve got to love the marketing
.....
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Old 13th June 2003, 06:34 PM   #20
Nelson Pass is offline Nelson Pass  United States
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EI Vs Toroidal transformers
Default Re: EI Vs Toroidal transformers

Quote:
Originally posted by pcn
While researching for power transformers, I came across the article http://www.soundstage.com/maxdb/maxdb071998.htm
This article makes one fundamental mistake: the assumption that different AC loading on the two phases of the secondary of your power distribution transformer results in DC. It does not.

What causes DC is asymmetric rectification, which commonly occurs when some appliance is controlled by a Triac or attentuated with a diode.

Dc does cause noise in toroids, and is a pain in the butt for high end manufacturers, where absolute mechanical silence is required. The solution generally revolves around some form of filtering or DC current limiting. Companies like Plitron, which we use, design their primaries more conservatively and also pot the mechanical assembly better. A thermistor in series with the primary also helps, as does dual rectifiers on the secondary.

As to the difference in sound between EI and toroids? The toroids, properly used, win every time for higher power applications.
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