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Old 31st December 2010, 08:15 PM   #41
kevinkr is offline kevinkr  United States
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I have until recently blindly followed the EI is better dogma, and while leakage inductance can reduce coupling of line born emi into the secondaries, the transformer construction also needs to minimize capacitance between the windings for this to be effective. I am not sure how often this is actually the case. (Split bobbin types are very good in this regard as well as leakage currents between the windings.)

An off the shelf combined common/diff mode choke from Coiltronics or Coilcraft and a toroid will probably offer superior EMI performance to a generic EI type, and in the case of the Antek the economics are very compelling.

I have recently replaced a number of EI type transformers in low voltage supplies with toroids because I got tired of their buzzing. The Anteks are silent under the same load currents, don't run nearly as warm, and generate much more benign magnetic fields as long as you do not saturate the core during any part of the cycle. Their voltage regulation under varying loads is often significantly better as well.

Best of all I hear absolutely no difference, and the great reduction in mechanical noise from those cores is a blessing I can hear quite easily..

I am less convinced that blindly using an EI transformer is always the right way to go, there are good engineering solutions that permit/recommend the use of toroids in specific situations. I like R-cores, but they are difficult to procure in the USA so I rarely use them.

Should you be very concerned about the effect of the commercial choke on the primary it is possible to wind air core chokes with sufficient inductance and low enough DCR to do the job nicely. I have not provably found the removal of these chokes to be audible and in the few cases where I thought I heard an improvement the fact that the removed choke had high DCR might have had a lot more to do with it.
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Old 1st January 2011, 02:10 AM   #42
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or Pieter trafo of course

Nice info Kevin ,you thinks that hammond split coils or 229 series are decent ?
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Old 1st January 2011, 02:57 AM   #43
Zekk is offline Zekk  Singapore
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Quote:
Originally Posted by Rundmaus View Post
Hi there,

a little OT, but where did you get that transformer? I need a 420-0-420 one at 180mA but it seems I need to have it custom-wound, as no one here offers these ratings off-the-shelf.

Greetings,
Andreas
Hi ... You got to have patience daily dredging Ebay!

Mine is a PEACO TF2RY0222 huge weather proofed tx. with 2X Pri. 115vac and 480-0-480 @ 500mA. Fully encased in epoxy!? Ugly and looks like a piece of rock. So, no bid but mine!

Costed me a staggering US$40.00 !

Enjoy but take care!

Zekk
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