If you are designing toroids at 1.2 T, then you are not getting many of the advantages that toroids can achieve. You may as well use a laminated core, not a toroid, as a laminated needs to run at about 1.2T. Toroids can run at much higher flux densities, which is the key to some performance improvements.
I reckon he's referring to the bandwidth of the transformer. 'More HF noise passed' implies wider bandwidth. Toroids have lowest leakage inductance (and highest inter-winding capacitance) which means they're highest bandwidth.
Happy to be enlightened if I've gotten this wrong.
I presume you mean this. The OP (and whoever else) should be sure to read the whole thing:
https://sound-au.com/articles/xfmr-dc.htm
This is sort of a loaded question. In a perfect world, 100% of the primary lines of flux cut through the secondary winding, and are delivered to the load. But in reality, a % of the flux is not coupled to the secondary winding, and escapes into the air. I refer to this as 'stray magnetics', (not leakage inductance, which has other parasitic components). In sensitive applications, such as a preamp, stray fields can cut across the low level input circuitry and induce noise into the system - which would later be amplified.
I'm not familiar with the term 'bandwidth' being associated with a 50 or 60 Hz power transformer. From my experience, bandwidth is a term used for audio input or output transformers that require to pass a wide frequency response. Among other attributes, they have a special interleaved construction that allow them to have a wide bandwidth.
A toroidal core is a nearly perfect magnetic element. Seriously! Clever design coupled with skilled machine operators can produce 'precision wound' toroids, have the lowest possible magnetic emissions. Although there is much confusion on this topic, the reduction of stray magnetics starts with 3 elements - core material, core geometry, and winding precision.
A skilled magnetics engineer should know how to achieve this. Hope this helps.
I'm not familiar with the term 'bandwidth' being associated with a 50 or 60 Hz power transformer. From my experience, bandwidth is a term used for audio input or output transformers that require to pass a wide frequency response. Among other attributes, they have a special interleaved construction that allow them to have a wide bandwidth.
A toroidal core is a nearly perfect magnetic element. Seriously! Clever design coupled with skilled machine operators can produce 'precision wound' toroids, have the lowest possible magnetic emissions. Although there is much confusion on this topic, the reduction of stray magnetics starts with 3 elements - core material, core geometry, and winding precision.
A skilled magnetics engineer should know how to achieve this. Hope this helps.
Toroids have much lower winding resistances that laminated transformers, which is key to their high efficiency
Due to their extreme high efficiency, and square hysteresis loop, toroids move abruptly into saturation, and have low tolerance to DC on the mains. In a toroidal core, all of the magnetic grains are aligned in the preferred direction, and there is not a gap. It is possible to gap a toroidal core, but it is a slow labour intensive process, and then a toroid would operate similar to a laminated core - thus not much point to gap a toroid.
Other types of cores, such as EI, L7, R, C-cores have what is referred to as a round hysteresis loop, meaning they move closer to saturation slowly, and dont saturate easily. In these configurations, airgaps are inherent to the core construction, so they are much less efficient than a toroid, and up to 40% of the grains are aligned in the wrong direction. This increased the core losses, and substantially lowers the efficiency, can run much hotter (which shortens the life of other components in close proximity), but a positive side affect is an ability to be less sensitive to adverse line conditions.
Its a trade.
Other types of cores, such as EI, L7, R, C-cores have what is referred to as a round hysteresis loop, meaning they move closer to saturation slowly, and dont saturate easily. In these configurations, airgaps are inherent to the core construction, so they are much less efficient than a toroid, and up to 40% of the grains are aligned in the wrong direction. This increased the core losses, and substantially lowers the efficiency, can run much hotter (which shortens the life of other components in close proximity), but a positive side affect is an ability to be less sensitive to adverse line conditions.
Its a trade.
So are we to interpret this as saying that talking about the 'bandwidth' of a mains transformer is inappropriate? The reason its of interest in the world of audio (quite apart from using a mains transformer as an OPT) is there's a fair amount of ultrasonic noise on the mains and it would be nice to have a transformer which doesn't couple this hash very well into our audio kit.
The same question, buzzing toroids, has been asked in this forum many times - all in different words. If you search publications, there seems to be contradictions and can be not totally accurate.
Core size is irrelevant to emitted noise, and its possible cores with a larger mass have the capability to be louder! In theory and books, a lacquered core is supposed to attenuate noise. In reality,
I have never found that to be an effective solution, and in fact vacuum varnishing degrades the properties of the core. The last stage in producing a toroidal core is annealing, where they run it through a furnace for 12 - 16 hours to remove stresses in the magnetic steel. Then if the core is varnished, that will re introduce some of the stresses removed in annealing.
If the noise changes daily, thats a reflection on the condition of the ever changing mains.
The best solution I believe is a simple DC blocking circuit. I know for a fact that many high end audio and video companies incorporate this in their products, so it has been extensively proven in the field and is invisible to the quality of the product. Then you have ALL of the advantages of a toroid - which are significant - with zero noise.
Hope this helps
Core size is irrelevant to emitted noise, and its possible cores with a larger mass have the capability to be louder! In theory and books, a lacquered core is supposed to attenuate noise. In reality,
I have never found that to be an effective solution, and in fact vacuum varnishing degrades the properties of the core. The last stage in producing a toroidal core is annealing, where they run it through a furnace for 12 - 16 hours to remove stresses in the magnetic steel. Then if the core is varnished, that will re introduce some of the stresses removed in annealing.
If the noise changes daily, thats a reflection on the condition of the ever changing mains.
The best solution I believe is a simple DC blocking circuit. I know for a fact that many high end audio and video companies incorporate this in their products, so it has been extensively proven in the field and is invisible to the quality of the product. Then you have ALL of the advantages of a toroid - which are significant - with zero noise.
Hope this helps
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