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EI Vs Toroidal transformers
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Old 11th June 2003, 08:23 PM   #1
pcn is offline pcn  United States
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Default EI Vs Toroidal transformers


I just joined this forum. Great forum, and very helpful people, including Mr Pass himself! I am planning on my first (from scratch) diy project, a pair of aleph 3 monos.

While researching for power transformers, I came across the article http://www.soundstage.com/maxdb/maxdb071998.htm
This article makes the case for using EI core transformers for better audio. Curious about your opinions on this subject.

I am getting the PCBs from Kristijan. The power supply that Kristijan suggests has a 2 x 21v 200VA transformer. I could only find a 2 x 18v 175VA EI core transformers. So, custom wound is my only option? I couldn't find any toroids neither with that specs. The aleph 3 service manual doesn't specify the specs for the transformer, but the rails are 25v. Please help me in finding a transformer.

Thanks for any help,
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Old 12th June 2003, 12:12 AM   #2
elizard is offline elizard  Canada
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try www.plitron.com and www.avellindberg.com for toroids
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Old 12th June 2003, 12:25 AM   #3
stokessd is offline stokessd  United States
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There's also Toroid corp of Maryland:


I like their kits which supplies you with a pre-made primary which you wind on whatever secondaries you want. The kit comes wiht a design guide and a final wrap. You supply the magnet wire for the secondary. Not real useful for standard types of transformers like the aleph units you want, but if you have a need for a lot of windings or odd voltages, they are handy.

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Old 12th June 2003, 12:29 AM   #4
elizard is offline elizard  Canada
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yeah, just checking the toroid.com website for their kits, very VERY useless when it comes to standard toroids .. $72 for a 400VA model???
i got a 400VA model for like $55 already wound for 2 secondaries

of course, if you do need odd secondary voltages, and odd # of transformers, then its a good deal
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Old 12th June 2003, 12:44 AM   #5
leadbelly is offline leadbelly  Canada
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OK, since I have already bought EI frame transformers for my amp, and I have read that reference link, I must ask ask:

How much spacing should I leave between the xformer bells and the signal path, or more precisely, how much spacing as a minimum? I am talking about 150VA xformers.
No one wants advice - only corroboration.
John Steinbeck
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Old 12th June 2003, 01:35 AM   #6
kiwi_abroad is offline kiwi_abroad  New Zealand
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The article doesn't make mention of another factor which is relevant in todays High-End systems: AC Filtering.
Although I can't recall details, I remember reading an article about the frequency responses of EI ve Toroidal AC power transformers, and it concluded that EI's were better as they had a vastly lower frequency response to EMI and 'hash' and thus acted as better AC line filters than Toroidals.
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Old 12th June 2003, 02:59 AM   #7
walker is offline walker  Australia
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Default Sound good but....

I read the article regarding the benefits of EI core transformers and thought, hmmm, nice attempt at explaining why some manufacturers use cheaper transformers. Great smoke and mirrors job!

Look out here comes the caveat; I'm not infallible but I do have both electrical and electronic engineering qualifications and 25 years audio experience.
The article reminded me of a very scientific paper that described the grain orientation of copper wire used for speaker cables. It stated that because the copper was DRAWN, (stretched through a die to make it the required thickness) in one direction the grains are directional and the electrons travel easier in this direction. Sounds good but 2 minor flaws, (read bloody great flaws!) The wire is drawn in both directions during manufacture and sound is carried by AC, electrons flowing in both directions equally!

OK, so back to the transformers, DC offset in AC power supplies is very very small and effects BOTH EI and toroidal transformers the same, they do not saturate the cores of transformers unless;
1. There is something VERY wrong with your supply and if there is expect some of your equipment to over heat and burnout.
2. The transformer has been made without enough core material, (read cheap) and that applies to both styles of manufacture!
I havenít heard everything on the subject Iím sure, but Iíve yet to hear a good reason to use EI core transformers in preference to toroids except COST. Iíd love to go on further but Iíve got a life to live and music to listen to.
So enjoy the music, both transformers work well, (usual ceveats),
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Old 12th June 2003, 04:39 AM   #8
Peter Daniel is offline Peter Daniel  Canada
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To answer your question about transformers, I will quote interview with John Curl, a designer behind Mark Levinson JC-2 and Vendetta preamplifier:
"When we talk about transformers we have to separate power amps and preamps. While they are not perfect, Toroidal transformers are logical choice for power amplifiers because they are very efficient, they tend to have a fairly low hum field, and they're readily available in large power ratings.
For preamplifiers and other line-level components, the old type EI transformers or what's called a D-core or split C-core transformer is actually better than a toroid. First of all, they tend to be more compact, and second, and perhaps more importantly, they have very low capacitance between the windings.
This can be a problem when Toroids are used in low level signal applications; the windings are on top of each other so they talk to each other. And today the AC power is so dirty. We fix that by using a transformer that isolates the winding, which is important on low level circuits. The old style EI or the new C- or D-core is the ultimate in that respect-as long as it is a dual-bobbin winding with physically separate bobbins for the primary and for secondary. It makes big difference in sound quality."
I'm only using split bobbin transformers for line level equipment now, never had problem with buzzing.
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Old 12th June 2003, 05:09 AM   #9
jh6you is offline jh6you
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Default Re: EI Vs Toroidal transformers

Originally posted by pcn

Curious about your opinions on this subject.
For the same power amplifier, I have tried both EI and toroidal.
To me, I feel as if EI gives a better relaxed sound (less tension) than toroidal. Personally, I prefer EI to toroidal for the sound.

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Old 12th June 2003, 07:31 AM   #10
walker is offline walker  Australia
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Default Can't argue with subjective posts:)

Can't argue with subjective posts, but that doesn't mean that they're wrong!
jh6you, your experiences are interesting, have you been able to evaluate the same amp designs with different transformers? Some thing I'll have to try some time.

EI for preamps, hmmm, I don't see that input filtering is the job of the transformer, just a benefit and EI's fix the noise problem by introducing another, as do dual bobbin transformers. A Faraday shield, (electrostatic shield), easily takes care of Capacitive coupling between primary and secondary windings. Both transformer constructions can have them included but I have to admit that I've seen more fitted to IE transformers than toroids. Again cost raises its ugly head.
If you have a noisy AC supply, fix it, don't expect the transformer to remove the symptoms. AC supply filtering isn't a black art, though at times it appears to be

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

Both transformer constructions still do a great job, enjoy the music, take care, regards WALKER!
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