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Old 5th February 2007, 04:00 AM   #31
BWRX is offline BWRX  United States
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Quote:
Originally posted by infinia
I think if one uses air coils esp. foils types the start of the winding (being the inner winding) should be the noisy connection or the input, and the end (outer) should be the quiet side or output connection. But please explain or elaborate what you mean in the quoted part above, in particular "start to end winding capacitance".
Agreed that the switching node should be connected to the start (inner) winding. Parasitic inductor capacitances were discussed in another thread (can't remember which one right now), and the two major ones to take into consideration are the interwinding and start to end winding capacitances. The interwinding capacitances are just that, the capacitance between each adjacent winding. The start to end winding capacitance is the capacitance between the start winding and the end winding. In a foil inductor the start and end windings are physically separated by all of the intermediate windings, which results in a low start to end winding capacitance. In a toroid inductor wound the whole way around the core with one layer of windings the start and end windings end up being right next to each other resulting in a higher start to end winding capacitance. Interwinding capacitance is a lot lower than a foil inductor, however.

Quote:
Originally posted by cotdt
Mundorf showed that miniscule vibrations on inductors generate a lot of distortion, and this problem is minimized with foil inductors. My listening tests tell me that air core inductors are indeed superior, and I never had a problem with EMI. I did shield my inductors, and also the Tripath chip itself.
Mechanical stability can be achieved with non-foil type inductors by dipping them in varnish. If listening tests tell you that air core inductors sound superior, than the cored inductors you used previously may have been saturating. Different size cores, materials, wire gauge, and winding technique can make all the difference.
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Old 5th February 2007, 04:07 AM   #32
cotdt is offline cotdt  United States
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Quote:
Originally posted by BWRX



Mechanical stability can be achieved with non-foil type inductors by dipping them in varnish. If listening tests tell you that air core inductors sound superior, than the cored inductors you used previously may have been saturating. Different size cores, materials, wire gauge, and winding technique can make all the difference.

This is definately worth trying out. About the saturation though, Tripath's own calculations showed that saturation should not occur with their recommended cored toroid, so I don't think that it saturated.
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Old 6th February 2007, 06:13 PM   #33
PWatts is offline PWatts  South Africa
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I'd be careful with foil coils. I used a 6.8uH choke in a full-bridge application, and the standing current was very high (100mA) due to the high capacitance. Switched to a normal wire version, still air-core, and the current dropped more than tenfold. Eventually I settled for a ferrite bar though, its lower DCR made the bass much tighter and the large airgap causes high powerhandling before saturation. However, that was for an open-loop application where the output impedance was of much higher concern than the self-oscillating feedback type ones predominantly used today...
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