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Filter Chokes wired for CMR

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Perhaps I missed it in a quick scan of this thread, but ...

A split choke wired for differential inductance but split between positive and negative rails has only its very small leakage inductance available to impede common-mode noise. Wired for common-mode inductance, it has only the small leakage available as a smoothing filter. To serve both functions at once you need two separate chokes on separate cores.

The late John Camille used two caps and a CMC as a single 4-pole capacitor, usually with ceramic capacitor bypasses on the caps. This is intended to solve the problem of capacitor inductance, which otherwise makes electrolytic caps especially ineffective suppressors of RFI. There is no significant effect in the audio frequencies per se.
 
For some reason CM chokes are regarded as sexy, so lots of people use them (or try to use them) inappropriately. Sometime they are used to remove almost non-existent CM noise, while (of course) not touching much greater differential-mode noise. Some people want to use them for choke input PSUs, not realising that for that you need a differential-mode choke (or just a plain choke). Finding that they can't be used as planned, some people then want to use the two windings as two separate chokes in a CLCLC filter - which in order to work requires zero coupling between chokes not tight coupling. And so it goes on.

I suspect that part of the trouble is that some people assume that if a component is only rarely used that is not because it is only rarely useful, but because 'engineers' only rarely realise how useful it is. Meanwhile, 'gurus' sprinkle the component into their circuits and proclaim its merits to their followers. Said followers don't understand why that is a daft thing to do.
 
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Perhaps I missed it in a quick scan of this thread, but ...

A split choke wired for differential inductance but split between positive and negative rails has only its very small leakage inductance available to impede common-mode noise. Wired for common-mode inductance, it has only the small leakage available as a smoothing filter. To serve both functions at once you need two separate chokes on separate cores.

The late John Camille used two caps and a CMC as a single 4-pole capacitor, usually with ceramic capacitor bypasses on the caps. This is intended to solve the problem of capacitor inductance, which otherwise makes electrolytic caps especially ineffective suppressors of RFI. There is no significant effect in the audio frequencies per se.

Thank you. This is more the sort of information I was looking for.

May I ask another question to fill out the picture a little? My guess is that leakage inductance reduces the amount of inductance available for the intended work the choke is to perform and so if you want a double duty choke the issue is one of wrestling with the ratios - emptying one pot to fill the other, perhaps necessitating a larger choke than usual if you want to get your differential inductance to be useful. Is that more or less it? ( I'm not really interested in pursuing this in practice now, just trying to learn something more about the inductor and the effects of its function.)
 
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