Iron cores of any type in a TPU? Every opinion stated about those thinking the small toroid is anything but a CMC or not containing a ferrite core... back at those thinking it is anything but iron-less... Really! Am I the only one seeing that the visible winding is ONE winding with reversed wrap direction in the middle? How many are aware the top of the line audio systems will not use an iron core cross-over coil because of the noise inherent from the Barkhausen effect? Testing the idea of it being a CMC is an easy task if you can make the use of a CMC work in your TPU concept. I have nothing to offer on that idea except I've wasted enough time trying to make a CMC fit in any TPU concept. Ok, since opinions are free.... I think it is an increductor. Yep, the name is worth Googling. This is an inductor with a semi-saturating core, using a high impedance winding with DC current in it to change the inductance. Or the winding is very low impedance and used high current for control of inductance of cross-over 'air' core coils. It's an old technique (usually nowadays this kind of thing is only used for flux-gate magnetometers) but a goodie. Also used in early television sets. Built with some imagination it can also act as variable signal delay line For those thinking about eBay'ing a bifilar voice coil - go ahead and grab the one most common... the ones that were used in the speaker basket with the radial magnetic field setup. The only bifilar dual voice coils I've ran into were two separate bifilar coils in one radial magnetic speaker basket. One of the coils was used as an output. I never bothered to find out what the output was for and doubt the information would be useful.
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