Use of Ferrite Cores for EMI Reduction???

Charles, the use of ferrite is pretty widespread in various electronic fields. There are many in's and out's as to where it can and should be used. The one main drawback to use of ferrite's has to do with saturation. Knowing the magnetic properties of the specific ferrite being used can come in handy. As such, you might want to experiment with use of ferrites on various cabling. Some manufacturers already include beads or clamps on some of their products.

I would not go crazy with quantities and pay attention to where you place them at. I would also mention that their use on power cords for high current items ( like power amps ) are more questionable than anywhere else, so keep that in mind. Sean
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You can buy a "billion" ferrite clamps in various sizes from either Digi-Key or Mouser ( can't remember which ) for the price of one small package of the Audioquest stuff.

Do a search through the old Greg Weaver articles on Soundstage and he even gives you part numbers. Some of these might not be valid anymore, but the dealer can probably cross reference them to current stock. They do have a minimum order, but it would still be less than buying a package of the AQ parts. If you can't find the part numbers, i'll try to look them up tonight or tomorrow. Sean
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Bob, out of curiosity, where was this cable located at within the confines of your system ? I have found that ferrite works best on digital based products. In specific, i'm talking about the power cords of transports, dac's, cd players, digital tuners, digital amps, etc... Like anything else though, try things in moderation. You CAN get "too much of a good thing" if you try ganging up multiple ferrite beads or clamps.

As many of you know, digital components are VERY noisy devices. Since they can pump their digital "hash" back into the power lines and other components, placing ferrites on the power cords at the component chassis helps to minimize this. Besides reducing the potential for the "dirt" to re-enter the AC system, this also reduces the chance of the device using the power cord as an "antenna" to re-radiate the rf based digital signal. This also works in reverse, as rfi is less apt to enter the device via the "power cord antenna" due to the impedance bump that the ferrite creates.

One thing that we have to make sure of when using ferrite based filters is that the cable remains centered in the ferrite choke. If the ferrite actually rests against or is closer to one section of the cable than another, it can produce an erratic filtering action. Not only does this reduce the efficiency of the ferrite as a filter, it can produce various loading conditions on the different polarities of the signal due to proximity effect. I would "assume" that this could produce a slightly "disjointed" or "un-natural" effect to music, possibly resulting in the lack of PRAT and tonal balance that Bob mentioned. This is not to say that this was what caused the problems he noted in his specific situation, only that it could be a possibility.

Since many ferrite chokes or clamps fit loosely over some cables, a ( cheap and dirty ) solution is to fill in the gap between the cable and ferrite with something that is "non-offensive". While the use of a paper towel cut into strips and then wrapped around the cable comes to mind, anything that is non-metalic or prone to static build-up should work fine. With the paper towel, etc... you can make as many turns necessary to take up the needed space. The clamp is then applied over the "spacer".

Not only can this keep the clamp more secured and keep it from sliding around on the cable, it should keep the gap between the ferrite core and the cable pretty evenly spaced. This is not a "test proven method" by any means but something that came to mind. If others have found better solution to this problem, PLEASE contribute your suggestions as you see fit. Sean
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Twl, the cables that you mention would be quite high in inductance. Then again, the treble roll off that takes place might somewhat balance out the somewhat leaner and brighter sound passed on by using such a fine gauged conductor.

I think that the guy that basically came up with ideas like this and pushed the envelope as we know it was David Magnan. He has gone to great lengths to minimize time smear, skin effect, etc.. in cables like nobody else that i know of. I've got a couple sets of his cables that make use of 36 gauge conductors that are air insultated and somewhat spaced apart. His newer designs don't even use wire at all, as they use some type of conductive "paint" to minimize skin effect. Never heard or used them, but some say that they are the ultimate. Sean
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Bringing conductors closer together moves them more towards being a capacitive load. Spacing them further apart makes them less capacitive and moves them more towards the inductive side of reactance.

When one can find equal amounts of capacitance and inductance at the same point, the reactance is effectively nulled. While this can be achieved, it typically varies with frequency. As frequency rises, wavelengths are shortened and the gap between conductors appears to widen. That is why zip cord is more inductive than a twisted pair given the same amount of insulation around each conductor. Both start out relatively even at very low frequencies but the gap between inductive reactance and capacitive reactance widens as frequency climbs.

The twisted pair has more intimate contact area between the two conductors as they spiral around each other. This increases capacitance / lowers inductance. The zip cord has only one continual point of contact along their lengths and is therefore more isolated from each other. As a result, inductance is increased and capacitance lowered.

As a side note, anyone that has tinkered with speaker crossovers knows that putting increased inductance in series with a speaker will roll off high frequency response. Hence, the lack of treble clarity and extension when using zip cord with thick insulation.

As one can tell, this is a very simplified example. If you want further proof, take some Goertz speaker cable and separate the conductors. Not only will it no longer be a high capacitance design, the total impedance will be drastically altered. Sean
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Twl, just running a "drain" aka "floating or telescoping ground" will alter impedance. I would therefore "assume" that putting ferrite over that would also alter it further. That is, at least within that small region where the ferrite was applied. After all, that what ferrite does. It creates an impedance "bump" within the nearfield.

As to specific ratios in terms of spacing vs capacitance / inductance, frequency and power levels, you've got the wrong guy. Better find someone that is both an EE and knows their physics : ) I'm WAY out of my league on stuff like that. Sean
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