Transformer: Toroid vs E-I

[a.wayne]

This is true with standard off-the-shelf toroidal transformers, but not necessarily so when you put an interwinding (electrostatic) screen in. Such screens are a must for high-end audio IMO. Sorry to nitpick, but it seems like toroidal TXs get a bad rap unnecessarily, if only because the utility of an interwinding screen is not well known in DIY circles, and not many manufacturers put them in their standard products for cost reasons.

Who does ...?

 

[jitter]

So, which one is better: E-I or toroid, weight and price consideration aside, only sonic benefit matters?

I couldn't tell from first hand experience, I never experimented.
I used a toroid for my DIY headphone amp because at the time I assumed it was the better choice. I was ignorant of the physics besides the low leakage of a toroid.
With the benefit of hindsight, I'm glad I chose the toroid because I housed the amp in a small case. I actually ended up hanging the toroid to the outside of the case because it still induced hum when it was bolted in the same place on the inside.
But for new DIY projects I would definitely consider EI-transformers.

So here's an answer: if distance to your circuits makes it necessary, a toroid.
To lower magnetic leakage even more, one of our customers orders a toroid with a sheetmetal iron ring around it. The idea is that magnetic leakage finds it easier to travel through the iron ring than the air around it (path of least resistance). Magnetic leakage is confined to the iron ring. When they still used toroids without the iron ring, they found that in some cases they had to turn the toroid slightly to lower induced currents to within allowed limits. Nowadays that's no longer necessary.

If E-I is really better and cheaper, then why most amps on the market use toroid? (Maybe making 2 chassis and using E-I is more expensive than using toroid in 1 chassis. But that doesn't explain why separate PSU's still use toroids.)

I think it's easier for a manufacturer to go with the flow and use a toroid when the customers expect to find one rather than swim against the current and use an EI.

 

[siliconray]

I just courious why nobody use toroid as output transformer? Because it's too difficult to wire the cables?

 

[jitter]

http://www.diyaudio.com/forums/tube...ansformer-output-transformer-tube-preamp.html

 

[Conrad Hoffman]

I think the use of toroids is largely a marketing ploy. Excellent designs can be done with both types. My personal experience is that the extremely low magnetic radiation of a toroid isn't as low as everybody would have you believe. Either type has to be located wisely in relation to the circuit.

 

[amptramp]

Representative toroid propaganda / specs / circuit designs can be found here:

Plitron

A neat design of a small amp using push-pull 50C5 outputs is here - using a toroid power transformer as the audio output transformer:

Of AC/DC Amps, Toroid Transformers and Small Size

The low leakage inductance of toroid outputs means you do not need capacitors or R-C snubbers across the plate-to-plate connections that are usually used for E-I transformers.

 

[data]

For amps a Toroid might be the better choice, but for low level applications like a DAC for example a EI will be more suitable, or even better... a C-core.