RFI chokes where to use and what to buy?
Posted by: Claus-Thoegersen on 24 July 2011
With my digital setup I have tried to understand all this talk about RFI chokes, with littleluck. Something about minimizing noise pollution into the system? Since these things should be cheap aobvious new tweek to play with, but where to buy and what types to look for? Help needs to be rather specific, because I either have to buy online from somewhere in the Uk, or try to translate brandnames and find something similar on the net or even locally IRL in Denmark.
Most any electronics supply store will have them. Here in the US, we have Radio Shack, but as they are a very common item, they can also be ordered through Amazon.
Simon recommended trying them on the ethernet cable, as it tends to act like a big antenna. I found two that were large enough, but since they were a slightly loose fit, I had to use a bit of Blu Tack to keep them from sliding down. Try one, or two, and see if you hear a difference. Keep adding until you no longer here any additional improvement.
I thought I heard a very slight improvement, but was not 100% sure. But you are right, they're cheap as tweaks go, so I figured better safe than sorry, and left them in place.
Good luck!
Hook
They pass lower frequencies and choke higher frequencies.
Search in the electronic suppliers under "magnetic components" (magnetiske komponenter) for "ferrite core" (ferritkerne) If you are putting them on cables with moulded terminations or terminations you don't want to pull apart and put back together again look for "snap fixing" types..
Look up RS 260-6492 to get the idea of the form factor of snap on ferrites. Dimension to suit your cable size(overall diameter) and RF filtering needs.
RS components have a Danish site, not sure if you need an account.
Manufacturers listed in RS include Wurth Electronik, Richco
Snap-on clamps are what you are looking for. 6.5mm will fit Ethernet and signal cables – 10mm will fit coaxial and power cables.
I have bought "Axial ferrite bead PA6 4.5-6.0mm cable" from RS Components and they fit perfectly on the LAN cable, whilst the "Axial ferrite bead PA6 7.0-8.5mm cable" fit well on other IC/digital cables.
All the responses are spot on.. In the non ideal real world, RF current flows down the shield. RF can't be simply earthed, as the physical distances are too small, and so it tends to spread where it can, and it spreads through conductors a lot more easily than air. However adding inductance to a conductor with RF will resist the RF current passing through that conductor. Therefore ferrite clamps add a small but usually worthwhile inductance to the shield or common mode conductors to impede the RF. Cables worth trying are mains leads, digital coax and interconnects. You can't really go wrong, and as the RF current is so tiny they never get warm etc.
RF if present can produce subtle distortion through affecting audio feedback circuits that can't keep up with the RF and can also produce tiny intermodulation currents (kind of like the opposite of harmonics) and these can produce very low level audible noise, hash or feedback distortion on the auduilines or power lines. The affects can vary depending on what the RF is affecting and can range from dulling the sound and robbing it of ambience, to making the audio sound sharp and overly bright.
In the end though if you can't hear any difference, then don't bother and you haven't wasted much money. For information I use woven RF impeding mains cables, a choke on my DC1 between my NDX and nDAC and rf filters on my nDAC to preamp interconnects, and now sit back and enjoy the music....
Simon
I tried some ferrite dampers on my LP12 signal cables (in to Superline) - given some nasty RF (but never UK based stations!). They seemed to 'muffle' the sound.
But I've heard good results on some speaker cables.
Hi,
I could buy from rs Components. Since it is mostly b to b, I had to put in a number used to identify a company but they are used to selling to customers in that way.
I have bought 2 chokes that will fit the digital cables, from my n-serve and Squeezebox receiver both connected to the Ndac. 2 others that can be used on the 2 cables going from the router to ns001 and the receiver. It seems different people are using chokes on almost all cables, so I think I will start with the digital cables later today when I have the time for a llong listening session.
Claus
Did it help?
they can be effective on 75 ohm dignal cables etc example cd to dac . place on dac end. on the remote end. mains cables at the appliance end
Thanks for this thread guys. I'll have to let the system bake in for a few days before declaring victory, but for $20 for a few ferrite rings, can't go wrong.
I've put 3-4 on the ethernet cable that plugs into my streamer and one each on my PC and Monitor electricity cables. The PC is in a separate room, but is on the same electric line. This is probably a cheaper version of running a mains line.
if correctly positioned they improve. used in sensitive industrial systems for decades
Can someone please clarify? I thought rfi chokes were meant to
be placed at the end of the component. If a cable is acting as an
antenna, would not the choke be placed just before the cable
enters the unit? Where do you place yours, Simon?
Thanks,
California Jim
Where would you place yours???..
The idea of a clamp on choke is that it adds reactance to radio frequency current that is flowing through the cable, ie it impedes the RF current and turns it to heat..
A) for coax, or shielded cables it impedes the current flowing in the shield.
B) for unshielded cables like mains leads or twisted pair cable like UTP Ethernet patch leads it impedes common mode RF current, ie current that is equally flowing through all the cables...
So where to put the clamps? Ideally you want to put the clamp closest to where the RF noise is emanating.
However life is not always that simple and cables can pick up RF, especially if you have noisy powersupplies, flat screen TVs or Ethernet over Powerline installations nearby, and also RF can be induced through the transformer effect in the shield from the legitimate RF signal in the core, like SPDIF leads.
Therefore
A) for noisy PSUs and TVs, clamp the mains leada closest to the noisy appliance to stop the lead radiating.
B) for digital sources with SPDIF or USB/Firewire clamp at the SPDIF/USB/Firewire source connector.
C) where you are wanting to protect the ingress of RF, clamp the SPDIF, USB, FireWire, Ethernet, mains lead closest to the device you are protecting.
Therefore for SPDIF I clamp at both ends, for mains and Ethernet leads I clamp closest to the device I am protecting.
I hope that helps, I would start at RF ingress points and work back until you hear no improvement.
Simon
Thanks, Simon, for that thorough explanation..!
California Jim
Simon, do you clamp powerlines as well?
Mat pip, in my set up I don't. I just put RF chokes on my SPDIF lead and Ethernet lead. For mains I use Belden and Powerline cables without chokes, and they seem to work well.
Simon
Understood. In my setup I have 3 ethernet cables in total: from wall to airport extreme, from AE to iMac, from AE to Squeezebox. One choke on the cable close to the Squeezebox should be enough right? or do I need to put 3 chokes, one on each cable (2nd and 3rd close to AE I guess). I know I could experiment, but don't wanna buy redundant stuff... thanks
Just read somewhere else that chokes are 3$ each...I guess I can experiment then 
but any advice is welcome anyway! cheers
Hi, best experiment, I found the Squeezebox very noisy electrically on its own and so you might find the choke on the Ethernet lead at the point it enters the Squeezebox has no or little effect. I wouldn't put chokes elsewhere on your Ethernet.
I'm using the sbt with a linear psu and it's not too bad. I've got the ethernet cable choked, and the electric cable choked too. Use a optical cable into the dac.