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Old 1st February 2007, 11:19 PM   #1281
Nixie is offline Nixie  Canada
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I'm using EI. Magnetic leakage of EI cores is easily shielded with nickel-iron alloy sheeting. The size is the only disadvantage, if you don't have the space. On the other hand, EIs have lower bandwidth and provide better isolation from mains noise, and do not buzz if there's some DC on the mains due to single-phase rectifier distortion etc. which is not that uncommon on household wiring; DC traps are rarely used with EI transformers.

If you're really cautious of magnetic leakage, use R-core; they have significantly less than a toroidal. Also, they have virtually no interwinding capacitance; other transformer types with windings on top of one another should have an electrostatic shield to avoid that.
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Old 2nd February 2007, 12:00 AM   #1282
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Quote:
Originally posted by Nixie
EIs...do not buzz if there's some DC on the mains due to single-phase rectifier distortion etc. which is not that uncommon on household wiring; DC traps are rarely used with EI transformers.

Not true. The loudest, most obnoxious transformer in the house is the EI in the UPS here by my ankle. It goes nuts at least four or five times a day now. Second loudest is the EI in the power supply in the rack in the lab downstairs. I can count on a good buzz around 13:00, plus a few others at random intervals during the day.
All my toroids are much quieter, regardless of manufacturer.

Grey
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Old 2nd February 2007, 01:28 AM   #1283
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That's very interesting, and contrary to my own experience, though I've only had two toroidal transformers so maybe my sample size is small. Both would buzz when I turn on some of the power tools in the workroom, which is not even on the same circuit. The EIs usually I rewind myself and I found that dipping the rebuilt transformer in varnish and putting a vacuum to it for about a minute, then drying over a week, removes any buzz so that it's only audible if I put my ear to it.
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Old 2nd February 2007, 01:45 AM   #1284
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HI
I use toroidal transformers from Plitron but I'm not sure if better than a good R-core transformer.
I used to see on Ebay 12V 300VA transformers . Victoria M transformers are very good quality .
Regards
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Old 2nd February 2007, 01:51 AM   #1285
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I forgot to mention, R-cores are also very easy to rewind, since you just spin the bobbin (building a winding machine for this is trivial trivial), which is possible due to the fact that the core is straight through the bobbin and has a round cross section. Adding or pulling a few top turns to/from a toroidal core is possible, but anything more is out of the question. EI cores, of course, have to be completely disassembled, although with some effort it is possible to remove some top turns (I've done it).
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Old 2nd February 2007, 03:39 PM   #1286
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Quote:
Originally posted by wuffwaff
Hi David,

the McMillan´s:

they are connected between the outputs (+ and -) and the sources of the input diff pair (R46 R47)
they are between 2k2 and about 10k
they form a feedback loop

suppose the outputs absolute output becomes positive. Now the current through the diff pair will become higher and the voltage over the drain resistors (R23 / R25) becomes higher.

Now the output fets will open up a bit (Rds gets lower) and the dc voltage at the output becomes lower.

It works the same way the other way round.

I tried different R´s starting from 2k7 and ending up with 10k. The higher the value is the better the sound quality will be and the higher the absolute dc startup value.

hope this simplistic explanation helps,

William
Thank you William!! Your thoughtful comments were extremely helpful for me and provided enough understanding to tinker and continue to learn.

BTW, overall you are a great DIYer on this site and have always enjoyed reading your helpful and insightful posts. The contribution of the Aleph and Alephx calculator are as indespensible as Duncan's PSU Simulator to me.

Thank you again,

-David
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Old 6th February 2007, 01:46 AM   #1287
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Default wiki and MBR3045WT

I was checking out the Wiki for the Aleph and came across a section that claims the author used 4X MBR3045WT IRF shottky rectifiers, These are comon cathode . How do you build a dual supply with these ? Dual secondaries?
how do you ground the supply?


J
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Old 6th February 2007, 10:18 AM   #1288
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Hi,

you could use them as one diode (parallel). Then you could make one bridge with four of them. Not shure about the advantage though........

William
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Old 6th February 2007, 11:26 AM   #1289
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Default ahh

It is the simple solution that escapes me, more current capacity may be the advantage ?

thanks
j
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Old 6th February 2007, 04:45 PM   #1290
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Unless perfectly matched, I've read paralleling rectifiers needs series resistors to enforce equal current sharing.
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