Are these line filters any good?

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If you have a particular problem to solve, these may do the trick for you. The layout of the components of the board looks like a "typical" power filter: a few caps, a coil, a few more caps, a coil, a few more caps.

The price seems a bit high to me as you can purchase EIC (power entry) filters or wired "inline" filters with the same ratings for $10-20, though these are much smaller in size than the one you linked. It looks good to me, but I'd be happier with a price closer to $20-30.

Eric
 
An ordinary IEC filtered input should be adequate. It deals with RF, which can sneak past big PSU capacitors. Any audio on the mains should be filtered by the PSU anyway - it can deal with 50Hz so 500Hz or 5kHz should be even better. That is why mains filters don't usually go that low - they don't need to! Always be wary of a salesman telling you about a problem you didn't know you had, especially if he offers just the thing to solve this 'problem'.
 
The eBay offering looks a tad over-priced (agree with Eric) - it has a couple of common-mode chokes and a handful of X2 caps and they want $50? Much cheaper to source the components yourself and build it. Choose the CM chokes according to the current demands of your amp. For CD players, DACs etc a lower current rating will in theory give better rejection as it allows higher inductance to be used. Self-resonant frequency is though an issue - when choosing CM chokes, look for those open framed ones where the windings are segmented, these do better at rejecting RF. Filters with Y caps are a mixed blessing, depending on how good your earth connection is - they may end up polluting your earth rather than cleaning your mains :eek:
 
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