I was just looking for a new trafo for a hiend DAC build and started wondering. There appears to be a degree of consensus that the best inductors for audio are foil type such as Mundorf/Jantzen/Duelund. And transformers are essentially inductors, just electromagnetically coupled. So why do we not have foil transformers?
Because of its distributed and coupling capacitances which are a lot higher...
They are in some cases. I have some 12 V 1KW transformers that have foil for the secondary.
Thanks @rayma , @Hearinspace - so it turns out I was wrong. Still, I see no power supply foil transformers and they were what I originally meant (was not specific enough, my bad).
Is this because of what @dreamth suggests?
Is this because of what @dreamth suggests?
I am not sure why that would be a huge deal?... I get that if there was inter-winding capacitance - that's bad because HF noise can get through. However this is easily solved by using split bobbins or otherwise separating primary from secondary. What am I missing?
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Yes , they are but they are used after careful calculations, usually in resonant smps , you don't just throw them in anywhere.
@uncle_leon
You're missing the Miller effect, LC resonances, etc...I know they look appealing, but they are used successfully only in very well calculated circuits.
You're missing the Miller effect, LC resonances, etc...I know they look appealing, but they are used successfully only in very well calculated circuits.
Other commercial examples, used in amps by Yamaha and Denon:
https://tocalaudio.blogspot.com/2019/01/restauracion-yamaha-pc-2602m.html
https://www.audioholics.com/amplifier-reviews/denon-pma-a100-integrated-amp-video
https://tocalaudio.blogspot.com/2019/01/restauracion-yamaha-pc-2602m.html
https://www.audioholics.com/amplifier-reviews/denon-pma-a100-integrated-amp-video
Would you be able to elaborate a little more? The Miller effect is pertinent to amplifiers, why this should be a concern for a PSU transformer? What kind of actual problems would LC resonances entail here? Loss of efficiency? Distorted output? I only know the basics of transformer operation so I'm asking because this is not obvious to me.
Foil windings are not useful for 60Hz power transformers.
There is no Miller effect in power transformers.
There is no Miller effect in power transformers.
Thanks for chiming in rayma, much appreciated. Can you pleae add a practical explanation why a foil power transformer is a bad idea?
Foil winding is definitely std practice in SMPS transformers for low voltage, high current outputs, not so much for audio transformers.
Standard 60Hz laminated or toroid transformers wound with magnet wire are much cheaper to make,
and foil types have no advantage there.
and foil types have no advantage there.
I recall testing some SMPS transformers while I was working and still in college (1982/83). They had a secondary that was 3/4” wide copper foil about 20 mils (1/2mm) thick. They were for someone like Nortel or Sperry. PITA to make. Very high current secondary.
I speculate that it would be very expensive to make a foil long enough to wind into a transformer. Assuming you can't draw out a ribbon or foil like you can a wire...
Plus then winding a foil rather than a wire would add another dimension to the complexity!
But if you were trying to be really clever and had a good marketing department, you would probably try hexagonal or ribbon wire for speaker voice coils.
Foil usually requires manually insulating the conductor. Ours were wound with a layer of Nomex™ simultaneously and manually. You also typically have to put the exit lead onto the foil prior to winding. This means you have to know the length of the winding in advance which requires very consistent winding tension.
"...if you were trying to be really clever and had a good marketing department, you would probably try hexagonal or ribbon wire for speaker voice coils...."
Dynaudio did the hexagon wire thing for at least some of its drivers as far back as the late 80's I think. 30W54 and 30W100 and several of others. Maybe that's to whom you were referring.
I have used square magnet wire (AWG10) for some big power transformers back when I worked in that business.
"...if you were trying to be really clever and had a good marketing department, you would probably try hexagonal or ribbon wire for speaker voice coils...."
Dynaudio did the hexagon wire thing for at least some of its drivers as far back as the late 80's I think. 30W54 and 30W100 and several of others. Maybe that's to whom you were referring.
I have used square magnet wire (AWG10) for some big power transformers back when I worked in that business.
Thank you guys. So the way I understand it now, foil power transformers are mostly just very difficult and costly to manufacture while having no obvious advantages. Having said that, they do not appear to be necessarily bad or inherently flawed. Which means they could, theoretically, have some hidden sonic advantages - the way some things, like cables, "sound" better with no obvious, measurable explanation.
Sooo... anyone up for a little community research? How about we build a few examples and put them to a listening test? I am happy to fund a couple transformer cores, dismantle some coils as a source of copper foil, and perhaps attmept to build some sort of foil winding contraption. But I would need help from folks who actually understand transformers and can help with the design and calculations. So that I don't end up shorting my mains or something.
Sooo... anyone up for a little community research? How about we build a few examples and put them to a listening test? I am happy to fund a couple transformer cores, dismantle some coils as a source of copper foil, and perhaps attmept to build some sort of foil winding contraption. But I would need help from folks who actually understand transformers and can help with the design and calculations. So that I don't end up shorting my mains or something.