Core choice for power transformer

[Joshua_G]

I'm about to order few custom power transformers, some for tube amps and some for SS amps, all are for phono stages and line stages. The choice is between E-I core, C core, R core and toroid transformers.

As far as I know:
Toroid are most efficient, but don't isolate well RFI between primary and secondary;
E-I core have better isolation between primary and secondary, but they are less efficient than toroid and their regulation isn't as good;
R core have best isolation between primary and secondary and better efficiency than E-I core;
Where does C core transformers stand?

[nac134]

High end audio applications are nearly exclusively Toriods, and some R cores.

[Joshua_G]

Originally Posted by nac134

High end audio applications are nearly exclusively Toriods, and some R cores.

Why do they use Toroids? Is it cost, or what? Toroids have worse RF isolation between primary and secondary.

[boyofwax]

For RF a mains filter is used. Toroids have the smallest magnetic field outside the core compared to ohthers.

[nac134]

Probably the most important single reason is that they produce less elecromagnetic interference in surrounding components. This will be especially important with small signal devices like phono stages - the other parts in the box will actually pick up the noise through the air in between. This is why it is best to keep the transformer as far away from other components as possible, or as many manufacturers do, house it in its own enclosure.

[mymindinside]

They are also lighter compared to E&I transformers. i think it is more how well the transformer is made.
cheers,
mymindinside

[imfree707]

Speaking of cores, I'd love to find a reasonable source for good audio cores and bobbins. I can't prove it, but I have an empathic intuition that solid-state push-pull amps, coupled with good transformers, emulate "Tube Sound". I built a 100 Watt PA amp about 30 years ago with PT iron OT and it sounds fine in PA use, runs directly on 12 Volts DC, idling at less than 500ma, drawing about 15 Amps at 100 W. Transformers are the levers of electricity!

[Joshua_G]

What are the benefits and drawbacks of R core and C core transformers?

[AndrewT]

I think Ccore have a (non)magnetic gap.
Both are more expensive.

Those that have reported Rcore performance usually rave about how well they do for low power operation.

[haltechrx7]

Hi
For ANY Audio Application I would Recommend a Toroid.
If you are concerned with Pri/Sec noise coupling you can always have a grounded "Electrostatic Shield" Between the two windings
Steve