EI Transformers vs Toroidal Transformers

[FrantzM]

Power amps with a toroidal mains power supply have a lower output impedance.

Why would that be? The output impedance has to be functional the output device’s and topology not not the transformer. Care to explain?

 

[levimax]

Power amps with a toroidal mains power supply have a lower output impedance.

I can vaguely see why because the PS secondary is in series with the output transistors but there are so many other things going on .... How much effect does the mains transformer really have?

 

[RayDunzl]

Power amps with a toroidal mains power supply have a lower output impedance.

Does that apply while the rectifier diodes are on AND off?

 

[LTig]

Power amps with a toroidal mains power supply have a lower output impedance.

Output impedance depends more on the capacity of the power supply caps than the transformer.

 

[audio2design]

2. EI Core has lower coupling capacitance between primary & secondary, so it blocks high frequency common mode noise from main AC far better than toroidal transformer
.

This is purely a factor of how either is wound. You can make a toroid with very low coupling capacitance too.

 

[audio2design]

Toroidal is expensive so they work at max possible flux (they saturate easily by over voltage). With correct design EI lamination is better and easy to repair, and the core is naturally grounded. No real advantage for typical audio application.
http://www.soundstagenetwork.com/maxdb/maxdb071998.htm

Most EI transformers have little in the way of effective air-gap so they saturate very similarly to toroids. Voltage does not saturate a transformer, current does.


That article you linked to is total crap. There are so many errors and fallacies I would not know where to start. That comment about grounding and draining energy from a saturated transformer was ... humorous.

 

[audio2design]

EI transformers have much lower in rush current on start up so you dont need "soft start" circuits for large VA transformers which saves a lot of trouble especially for DIY. These "soft start" circuits all have some potential safety / reliability issues.

No. This is only true if you are pushing the transformer past saturation which you should never be. < Saturation it comes down to inductance mainly.

 

[pma]

Could you post an example of the power toroidal transformer with low intrinsic stray capacitance, other than the one with a shielding foil, that must be connected somewhere and only shifts the issue.

 

[levimax]

No. This is only true if you are pushing the transformer past saturation which you should never be. < Saturation it comes down to inductance mainly.

I am talking about " in rush current" when you first switch on an amp. Large torroids draw huge current and require "soft start" circuit to mitigate this. EI dont have this issue.

 

[preload]

Also, I'm pretty sure the McIntosh solid state amps don't use toroids, either.

McIntosh amps don't need to use toroidal transformers due to their usage of blue VU meters.

 

[watchnerd]

McIntosh amps don't need to use toroidal transformers due to their usage of blue VU meters.

Luxman SS amps have VU meters, too, and no toroids.

Hmmm...you may be on to something.

 

[RayDunzl]

McIntosh amps don't need to use toroidal transformers due to their usage of blue VU meters.

My little antique Krells have toroids but no VU.

It must be a trend.

 

[watchnerd]

My little antique Krells have toroids but no VU.

It must be a trend.

Well, the Yamaha referenced at the top of the thread blows up the trend -- it has both VU meters and a toroid.

Although they're not really great VUs....

 

[Rock Rabbit]

The toroidal construction provides the transformer operation without acoustic noise, while the vibration of iron laminations can produce acoustic noise. But the price of the toroidal transformer is higher than lamination core transformers. The toroidal transformer construction makes them much more expensive to manufacture. Wire winding requires more complex and slower equipment.
https://www.electrical4u.com/toroidal-transformer/

 

[watchnerd]

But the price of the toroidal transformer is higher

I thought @levimax said this point about price is no longer true.

 

[MediumRare]

I think most tube amps use EI transformers? Or at least some other non-toroidal kind.

Also, I'm pretty sure the McIntosh solid state amps don't use toroids, either.

Yep. Better for impedance matching, too. https://www.manualsdir.com/manuals/117061/mcintosh-mc1201.html?page=14

 

[Rock Rabbit]

I thought @levimax said this point about price is no longer true.

Marketing is everything, the machine to make coils on a toroid is expensive, with good marketing "low noise" "low losses" etc the price of toroidal transformers is "competitive". Nobody selling toroidal transformers gonna tell they can go easily in saturation, tend to work hot, have more in rush current....marketing could make this issues irrelevant to non technical people

 

[watchnerd]

Marketing is everything, the machine to make coils on a toroid is expensive, with good marketing "low noise" "low losses" etc the price of toroidal transformers is "competitive". Nobody selling toroidal transformers gonna tell they can go easily in saturation, tend to work hot, have more in rush current....marketing could make this issues irrelevant to non technical people

If you're buying OEM parts, the price from the maker is your BOM price. His cost of production doesn't matter to you.

And @levimax seems to be saying that toroids are cheaper parts to buy now, unless I'm misunderstanding.

 

[levimax]

If you're buying OEM parts, the price from the maker is your BOM price. His cost of production doesn't matter to you.

And @levimax seems to be saying that toroids are cheaper parts to buy now, unless I'm misunderstanding.

For DIY Antec torroids are cheap and they have a huge number to chose from and they are in stock. It is hard to even find large EI transformers for power amps for DIY. Maybe it is different for the commercial OEM market but I doubt it... The volume has gone to torroids. My understanding is that Antec has high speed automated equiptment and can really crank out torroids. All they really are is wire wound in a pattern..no cores, brackets, etc. so with the right equiptment they are cheap to make.

 

[Rock Rabbit]

If you're buying OEM parts, the price from the maker is your BOM price. His cost of production doesn't matter to you.

And @levimax seems to be saying that toroids are cheaper parts to buy now, unless I'm misunderstanding.

But doesn't mean toroidals are better, used at high magnetic density (necessary for competitive price) in power supply applications with poor mains regulation they simply are a nightmare...add that to the BOM and reliability of the design (transformer thermal issues, short insulation life, unexpected repetitive blown fuses) or worse as forced use of slow blow fuses in electronics!.
I hope the central idea is EI vs Toroidal real technology comparison