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Old 14th April 2013, 03:08 PM   #51
dmills is online now dmills  United Kingdom
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The best approach is probably to design the audio card on the assumption that the power rails have all sorts of hash over the range of a few Hz to a few hundred Mhz, and design the card on board regulators and filtering to cope, not that hard.

Ferites and smallish smt caps go a long way at high frequency (Where regulators tend to have poor PSRR), I would be leery of adding large amounts of bulk capacitance to the rails on the PCI bus as that can bite you with regulator stability and also start up sequencing (Plus an add on card full of caps will be electrically too far from the load to help at more then a few Mhz).

Regards, Dan.
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Old 14th April 2013, 03:37 PM   #52
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I too am a big fan of ferrites but would advise being very careful if using any on the decoupling of an oscillator.
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-Antonio
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Old 14th April 2013, 04:17 PM   #53
dmills is online now dmills  United Kingdom
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Why? A little shunt R will kill the Q, and most SMT RFI ferrite becomes appreciably lossy at high frequency anyway by design, I routinely use them in power isolation for low phase noise crystal oscilators and seldom see a problem.

Granted a -2 mix or something would probably not be a great idea for power isolation at, but the more common high mu mixes used explicitly for RFI supression don't tend to have too much in the way of annoying self resonances below the point at which they become resistive.

Regards, Dan.
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Old 15th April 2013, 12:29 PM   #54
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Quote:
Originally Posted by dmills View Post
Why? A little shunt R will kill the Q, and most SMT RFI ferrite becomes appreciably lossy at high frequency anyway by design, I routinely use them in power isolation for low phase noise crystal oscilators and seldom see a problem.

Granted a -2 mix or something would probably not be a great idea for power isolation at, but the more common high mu mixes used explicitly for RFI supression don't tend to have too much in the way of annoying self resonances below the point at which they become resistive.

Regards, Dan.
Dan,

I cautioned about using them with care, as you do.
My motivation was a lesson learned related to a switched turn on of the oscillator power. Oscillators dont start from their final resonant frequency so one does need to ensure there are no lower frequency resonances.

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-Antonio
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