Are toroidal transformers best?

[anatech]

Hi ilimzn,
It seems to me that they could wind in a modified EI core fashion and slip them on before gluing the cores together. This should reduce the cost.

At this point we can start thinking good output transformers for tube amps.

-Chris

[jsa_ind]

Hello Guys,

What abour "R" core transformers are they better than the rest ?

Please advise.

Thanks,

Regards,

Junia.

[jsa_ind]

Opps sorry one of the links for R core are http://www.electroassemblies.com/r-core.htm

[anatech]

Hi jsa_ind,
I've seen those in inexpensive products from the 70's. Tenco or Alexander may have been the brands.

Nothing new under the sun I guess. Those would be prime for gapping though.

-Chris

[ilimzn]

Actually, Chris, they wouldn't. The R-core has the same single piece, gapless construction as the toroid. The difference is in the winding method. The toroid normaly requires a rather complex and interesting machine to wind it, while the R-core avoids this by the use of a round core cross-section, which alowes a bobbin to be assembled on the core in two halves. The bobbin itself has teeth on the sides like a gear, which are used to turn the bobbin on the core and thus wind the wire onto it. In all other respects save perhaps a slightly elevated stray flux, it is like a toroid. In fact, it is eminently possible to wind an R-core on a toroid winding machine, without bobins. Trying to cut the R-core is the same as cutting a toroid core, both are wound out of one piece of metal. Te difference is that with the R-core, the width is varied from end to end, so that when wound, the cross-section becomes circular.

[anatech]

Hi ilimzn,

while the R-core avoids this by the use of a round core cross-section, which alowes a bobbin to be assembled on the core in two halves. The bobbin itself has teeth on the sides like a gear, which are used to turn the bobbin on the core and thus wind the wire onto it.

I hadn't thought of that. Thank you! Neat concept.

I understand that the core can be fine cut and polished with a desired gap for toroids. This core just looks easier to do that with (end pieces). With this you can access the core without damage to the windings.

-Chris

[ilimzn]

Originally posted by anatech
Hi ilimzn,
I hadn't thought of that. Thank you! Neat concept.
I understand that the core can be fine cut and polished with a desired gap for toroids. This core just looks easier to do that with (end pieces). With this you can access the core without damage to the windings.
-Chris

Yes, that much is true if the windings are to your liking
Toroid cores can be cut the same way, but they need to be cut before the transformer is wound - this would be the ideal scenario for a R-core too

[anatech]

Hi ilimzn,

Toroid cores can be cut the same way, but they need to be cut before the transformer is wound - this would be the ideal scenario for a R-core too

Absolutely!
No, they are not to my liking.

-Chris

[walker]

You should not have anywhere near enough DC in your AC supply to cause core saturation in any type of transformer. If you do you need to get something done about it before something gets damaged or overheats and causes a fire! Please take that seriously.

The mechanical buzzing that a transformer produces is either caused by mangestriction or stray flux moving a magnetic surface, both poor design/manufacture, not core type. In my 30 years experience EI cores tend to produce more noise from both causes.
I'm not saying that a cheap torroid will allways be quieter than a quality EI.

Electrical noise introduced into the amplifier chain usually comes from; earthing issues, stray transformer flux, poor filtering or poor power supply rejection ratio.
If you are getting electrical HF noise into your amp check earthing.
If the electrical noise is caused by the transformer, encase it in a magnetic sheild, wrap it with a flux strap, use a toriod or do all, (though that may be over kill Poor filtering and PSRR not a transformer issue.

All core types can saturate but should not do so, (see 1st parragraph). An EI core transformer with an air gap, (note manufacturers try to keep the gap as small as possible so that it's effect will be minimised), will often saturate before a torriods. It depends on how conservitively the core has been designed, not on the air gap.

I'm still to hear any advantage for an EI over a torroid.

OOPS, I'll admit it, there is an EI advantage; they're usually cheaper!

NOTE There are flux leakage transformers with large gaps, ie AC welders, discharge lighting, magamps... We are not discussing these types and they would not be suitable for an amplifier.

Sorry if I'm being a bit long winded, regards
Walker

Passionate, not heated

[anatech]

Hi walker,
In my experience with audio equipment, spanning over 30 years, I have formed an opposite opinion to yours with respect to core saturation.

I do agree that all transformers can be noisy. That includes toroids.

The only advantages a toroid can have are a lower profile (allowing less rack space to be used), and normally lower external flux.

I would be interested in hearing a good toroid as an output transformer, but I think that gapping would still be prudent. It's not a perfect world we live in.

You should not have anywhere near enough DC in your AC supply to cause core saturation in any type of transformer.

Well, saturation is a reality with mains transformers. Are you going to solve this on the distribution side, or your smaller transformer design? It's not a problem for heavy industry (that's where the money is), so I'm guessing the small transformer manufacturer had better start dealing with these issues. EI core types are not affected as much.

-Chris