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Old 4th February 2011, 02:40 AM   #101
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Originally Posted by abraxalito View Post
Why do you want a medical grade filter? They have low leakage because when the equipment is connected to patients, there's a more acute shock hazard. For audio you don't want a medical grade filter, they're compromised for that reason.
Yes , I noticed the tyco med. grades use better caps with lower values , higher resistance values .... trading leakage for HF rolloff and general performance.Yes, Yet another thing to consider.

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Old 4th February 2011, 03:42 AM   #102
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When you're using a filter with Y caps (that's the ones from line to earth), your attenuation is only going to get as good as the earth connection you have. Which in most cases is inductive and several uH. So in my view Y caps aren't really worth bothering with - they're impossible if the kit is class II anyway. Ferrites are the way forward.
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Old 4th February 2011, 03:46 AM   #103
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Ferrites are the way forward.
Where would you put them?
Circuit please. The web is lacking in discrete RFI filter material ... only finished modules. Just a general idea , I am good at "filling in the blanks".
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Old 4th February 2011, 03:51 AM   #104
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Well they'll probably be used as the core of the common-mode choke, so they're already there. We just need to make sure they're the right kind. Usually ferrites are chosen for having low loss. Here we definitely want the opposite - ferrite with lots of loss! I wonder if non-laminated steel would have an effect at the lower frequencies, we might need several filters in series each targeting a particular freq band. Higher frequency ones first (nearest the inlet).
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Old 4th February 2011, 03:56 AM   #105
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Just a basic drawing , I already have the filters plugged into LT with both common and diff. AC sources.
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Old 4th February 2011, 04:02 AM   #106
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OK, I'll work on it over the next day or so and post up a sketch with suggested filters and coils.
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Old 4th February 2011, 09:03 AM   #107
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Originally Posted by abraxalito View Post
Why do you want a medical grade filter? They have low leakage because when the equipment is connected to patients, there's a more acute shock hazard. For audio you don't want a medical grade filter, they're compromised for that reason.
What's wrong with low leakage? I dont understand how this would be a neg and not a pro...
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Old 4th February 2011, 09:07 AM   #108
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We are discussing the "culprits". Let's look at what they do to the mains.
I discussed this subject with a friend and we came to the conclusion that EACH offender on the same line then the hi-fi system must be filtered with a good, discrete RF filter of size proportional to the power consumed.
Prevention sometimes is better than cure.

Besides, a way to filter the GROUND is needed for all audio equipment that do NOT use a SMPS psu themselves.
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Old 4th February 2011, 11:29 AM   #109
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What's wrong with low leakage? I dont understand how this would be a neg and not a pro...
If you compare the two versions of a pre-built mains filter, the normal one and the medical variant, you'll find there's a difference in rejection of noise. That's because the values of Y capacitors are smaller in the medical variant, hence less HF filtering effect. On reflection, this isn't always bad for audio, its only bad where there's a good earth which can be used as a sink for the interference. If the earth is poor, or non-existent (as for a class II setup for example) then a medical grade filter could well be better.
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Old 4th February 2011, 01:12 PM   #110
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Here's an interesting paper I dug up as a result of the issue coming up on the JC Blowtorch thread. I offer it here to those interested in the effects of RF on IC amps:

http://www.analog.com/static/importe...als/MT-096.pdf
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