Where to Buy Ferrite Rings? - AVS Forum
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post #1 of 12 Old 11-27-2009, 11:22 PM - Thread Starter
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Hey guys, I"m trying to eliminate RF interference on a set of computer speakers. Anyone know a good source for Ferrite Rings or NP0/C0G ceramic discs? And what ohm specification should I use for this application? Thanks
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post #2 of 12 Old 11-28-2009, 07:44 AM
 
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And what ohm specification should I use for this application?

Ferrite cores increase lump inductance. Inductance is measured in Henries. Capacitance is measured in Farads. Resistance is measured in Ohms.
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post #3 of 12 Old 11-28-2009, 09:18 AM - Thread Starter
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OK. But when I did find a website that sold the ceramic rings it had them listed with different ohm ratings. I can't find the website again or I would link it
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post #4 of 12 Old 11-28-2009, 11:52 AM
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The ohms rating may have been the impedance at some specific frequency.

You should be able to find what you need at any electronics store (a real one, not the Shack). On-line, try Digikey or Mouser.
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post #5 of 12 Old 11-29-2009, 08:00 AM
 
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Quote:
ceramic rings

You asked about ferrite cores and ceramic disc capacitors.
Reactance is measured in Ohms, but it's frequency specific.
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post #6 of 12 Old 11-29-2009, 10:36 AM
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Digikey and Mouser are both great sources for ferrite cores and other electronic parts.

In reality cores on interconnects are a band-aid and often applied as a list ditch effort to pass FCC emission standards. (been there, done that)

A 'phile and his money are soon parted...
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post #7 of 12 Old 11-29-2009, 10:23 PM - Thread Starter
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OK. So I'm guessing an in-line power line filter would work better? Eliminating the radio waves being picked up by the cable is not an option, as I live next to radio towers. Does anyone make a power line filter with a regular AC outlet receptacle on one end and an AC plug on the other? In other words, a "plug n play" option for the power cord of the speaker set?
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post #8 of 12 Old 11-30-2009, 08:29 AM
 
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Are you sure the RF is getting in through the power line?
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post #9 of 12 Old 11-30-2009, 09:25 AM - Thread Starter
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Originally Posted by duvetyne View Post

Are you sure the RF is getting in through the power line?

Not entirely sure, but my guess right now is that it is an AM, rather than an FM station being picked up. The length of the power and speakers cables going to the speaker set are both too short to pick up AM frequencies, so if its an AM station, it's got to be the house wiring that is acting as the antenna. Filtering it after the power comes out of the outlet would then solve the issue.
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post #10 of 12 Old 11-30-2009, 11:19 AM
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Well in this application a ferrite on the power cords might just be the ticket.

A speaker alone can not demodulate RF.

The RF is probably entering through the power lines and being "detected" by the rectifiers in the power supply or even a P-N junction in an IC or bipolar transistor in the amplifier circutry.

Your close proximity to the towers is going to make it very difficult. Worst case the RF is entering right through the speaker case (I am guessing plastic) and no amount of filtering will stop it. More drastic measures including grounded RF shielding my be necessary.

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post #11 of 12 Old 11-30-2009, 02:06 PM - Thread Starter
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The amp for the speaker set is built into the sub box. The satellites go from there. Yes, the sides of the sub and satellites is plastic. How can I construct a grounded shield for them, and what kind of ferrite rings should I get for the cables?
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post #12 of 12 Old 11-30-2009, 06:55 PM
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Originally Posted by gfhoward View Post

The amp for the speaker set is built into the sub box. The satellites go from there. Yes, the sides of the sub and satellites is plastic. How can I construct a grounded shield for them, and what kind of ferrite rings should I get for the cables?

I would start with something like this snap over core. This is just an example you can probably find them cheaper but with shipping it's a wash because ferrite cores are heavy.

Go for a big core and wrap the line cord through it as many times as you can. Try to keep the core as close to the amp end of the cord.

As for shielding any thin sheet metal or fine mesh screen will work, but copper is probably the best for RF but aluminum also work. The main thing for the shielding is it will have to be EARTH grounded to be effective. The screw in the center of a three prong outlet cover should be connected to ground. There is always the classic cold water pipe or a six foot copper rod hammered in to the ground.

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