This thread is where we can discuss transformers, power supplies, noise etc. Lets limit the discussion to off mains types, so not SMPS.
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Wow this can be huge.
We have all sorts of core types (UI; EI; single and double c-cores; toroidal cores; R-cores to name the most important).
There are different grades of steel.
Core excitation (properties of low core excitation; risks of core saturation).
(Vacuum) impregnating of windings.
Potting of transformers.
Screening; interwinding screens.
And more....
We have all sorts of core types (UI; EI; single and double c-cores; toroidal cores; R-cores to name the most important).
There are different grades of steel.
Core excitation (properties of low core excitation; risks of core saturation).
(Vacuum) impregnating of windings.
Potting of transformers.
Screening; interwinding screens.
And more....
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OK, to open up:
Because questions/problems regarding toroidal power supply transformers pop up repeatedly, here once more what I posted over three years ago:
"The difference between stock toroidal power supply transformers and so called "audiograde" toroidal power supply transformers is not specified.
What generally is meant with "audiograde" is that manufacturers use transformers with higher power rating than necessary for the job.
Toroids are very efficient transformers because of their electromagnetic geometry; form and absence of air gap mean comparatively low power loss.
This means that, for a given power, toroids are smaller than their EI or whatever counterparts.
Another "technical" advantage is that toroids have rather low strayfields.
Dimension and weight are important economic reasons to use toroids.
The problem however with many toroids is core excitation, expressed in flux density T.
Everyone using toroids is familiar with the inrush "oomph", requiring NTC resistors or other means not to blow fuses, and sometimes "DC blockers" to prevent core saturation.
This high inrush current comes from the fact that, because of the efficient electromagnetics, the toroid responds instantaneously when line voltage is switched on.
EI, and other transformers with some sort of airgap and/or less efficient geometry respond less brutal; they therefore have less inrush current.
Winding toroids with less inrush current is not so difficult but normally not done.
To do so, flux density must remain low, preferably maximum 1 T, instead of the "standard" 1,7-1,8 T for off the shelve toroids.
For lower flux density it is necessary to wind more turns on a given core.
More turns mean more required winding space, hence a larger core is required for a low T toroid with the same power as a "stock" high T toroid.
So here "better" is larger, heavier, more expensive.
When you need a high quality toroid with even lower strayfields, find one with low T, and preferably a screen between primary and secondaries (ask the manufacturer for the specs).
A very good, but less acknowledged alternative in the "audiophile" arena is a power supply transformer wound on a c-core (in between toroid and EI for efficiency).
With a c-core it is easy to apply minor air gapping to prevent hectic inrush current, so we don't need NTC resistors or other "inrush current fighters" and DC blockers.
Besides, unlike toroids, c-core transformers (like EI transformers) can be wound tightly, with no "crossing" of windings, so there is less risk of noise caused by resonance (Monolith Magnetics is a manufacturer doing high quality c-core transformers)."
At that time member Bonsai recommended a British brand of toroids (Tiger?) exactly because of their lower core excitation and screen between primary and secondary.
Because questions/problems regarding toroidal power supply transformers pop up repeatedly, here once more what I posted over three years ago:
"The difference between stock toroidal power supply transformers and so called "audiograde" toroidal power supply transformers is not specified.
What generally is meant with "audiograde" is that manufacturers use transformers with higher power rating than necessary for the job.
Toroids are very efficient transformers because of their electromagnetic geometry; form and absence of air gap mean comparatively low power loss.
This means that, for a given power, toroids are smaller than their EI or whatever counterparts.
Another "technical" advantage is that toroids have rather low strayfields.
Dimension and weight are important economic reasons to use toroids.
The problem however with many toroids is core excitation, expressed in flux density T.
Everyone using toroids is familiar with the inrush "oomph", requiring NTC resistors or other means not to blow fuses, and sometimes "DC blockers" to prevent core saturation.
This high inrush current comes from the fact that, because of the efficient electromagnetics, the toroid responds instantaneously when line voltage is switched on.
EI, and other transformers with some sort of airgap and/or less efficient geometry respond less brutal; they therefore have less inrush current.
Winding toroids with less inrush current is not so difficult but normally not done.
To do so, flux density must remain low, preferably maximum 1 T, instead of the "standard" 1,7-1,8 T for off the shelve toroids.
For lower flux density it is necessary to wind more turns on a given core.
More turns mean more required winding space, hence a larger core is required for a low T toroid with the same power as a "stock" high T toroid.
So here "better" is larger, heavier, more expensive.
When you need a high quality toroid with even lower strayfields, find one with low T, and preferably a screen between primary and secondaries (ask the manufacturer for the specs).
A very good, but less acknowledged alternative in the "audiophile" arena is a power supply transformer wound on a c-core (in between toroid and EI for efficiency).
With a c-core it is easy to apply minor air gapping to prevent hectic inrush current, so we don't need NTC resistors or other "inrush current fighters" and DC blockers.
Besides, unlike toroids, c-core transformers (like EI transformers) can be wound tightly, with no "crossing" of windings, so there is less risk of noise caused by resonance (Monolith Magnetics is a manufacturer doing high quality c-core transformers)."
At that time member Bonsai recommended a British brand of toroids (Tiger?) exactly because of their lower core excitation and screen between primary and secondary.
Canterbury Windings offer low flux density design for custom builds. Not sure if they are still operational. Hope so, good quality units.