• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

RCA cable Magnetic interference measurement and comparison

About the ferrites, do you know how much different "mixes" make?
It can make a difference. For this application you want maximum permeability (and therefore maximum "AL")
But the generic random cheap ferrite clamps seam to have okay AL/€
Good ferrites might me 4-10 times better but they are often more then 10 times the price to.

The one i have cost 2€ for 10pcs and the have an AL of ~4µH ( i don’t know material/mix)
You might find a core with 10µH but its likely cost way more.
 
I need to tell a story with an "audiophile" cable with ferrite filter that I bought from Amazon.

I've bought the cable some time ago and was very pleased with the sound because I actually think that there is an audible difference to the cable that I've used before that.

Then I bought a new amp and a new streamer. A Billie MKII amp and an Auralic streamer. The sound of this combination was outstanding. I've also experimented a bit with different cables. For whatever reason I had the impression that the ferrite filter cable sounded best.

Then a weird phenomenon occurred and I did spend days to figure out where it was coming from. Using the Billie remote control it suddenly had a weird, pretty hefty volume bump up when I was trying to change the volume. No matter if I was turning the volume up or down. First I thought it was the remote, then the Auralic remote learning function, then the tubes, then the specific input, then the power conditioner, etc. I went down a rabbit hole for days and could not figure out what had happened. I already contacted Auralic and Heaven 11, the manufacturer of the Billie amp. They both tried to help me, but we couldn't find out what was causing the problem.

I was already thinking of sending the Billie amp back for repair - and then I suddenly had the idea that it was neither the amp nor the streamer - and that I might have maybe connected the cable in the wrong way. There are little arrows on the ferrite filter which show the supposed signal flow. I actually found out that I had connected it facing into the wrong direction.

Then I switched the direction - and the whole annoying volume bump problem was gone. I have no idea how that is possible, but that's what happened.

Maybe someone can explain this behavior to me...
 
Last edited:
A 'ferrite' is non-directional.
The signal in a cable is bi-directional.
Both signal conductors need to go thru the same 'ferrite'. If only one conductor goes thru a 'ferrite' it can saturate.
 
A ferrite is non directional but the position where it is on the cable can matter depending if the source of the unwanted interfering signal is making it directional per usecase.
When the ferrite is in the middle of the cable it should not matter. It could matter if there is only 1 ferrite near one end.
Then the question is what ferrite material is used. Not all ferrites have the same permeability and may be suited for specific frequency bands.
Single winding, multiple winding all matters as well.

When the cable is screened the ferrite only increases the impedance of the screen locally (which can lower ground loop currents) and the inner wire is not affected.

For the audio signal going into a device being say ... 10kohm an increase in cable impedance above a certain frequency won't change the audio signal but for a HF current through the screen the current would be lowered which is what ferrites are for. Digital audio transmission is HF b.t.w.

When a specific cable is supplied with a device and, for EMC reasons, it is required to be used with that cable it can matter how the cable is connected to that device in which case there can be an arrow on the cable to ensure the device passes EMC regulation (usually for emission).

In this particular case the question would be what else changed at the same time.
Did the cable have the shield only connected on one side (and 2 internal wires where one is common and one is signal and only those are connected on both sides making the cable itself directional ?

When you change the direction again does the fault condition occur immediately and reliably again and not in the 'right' direction.

HF problems can be nightmare to trouble shoot when one does not understand the theories behind it.
 
Last edited:
a] If the cable is an interference receiving antenna, the ferrite should be placed at the input end of the cable.
b] If the cable is an interference transmitting antenna, the ferrite should be placed at the output end of the cable.
c] For the best interference rejection, the shield should be connected at both ends.
 
When it comes to SMPS's there's the good, the bad and the ugly.
When it comes to audio input & output stage circuit design, there's the good, bad and ugly.
 
When it comes to SMPS's there's the good, the bad and the ugly.
When it comes to audio input & output stage circuit design, there's the good, bad and ugly.
Yep, agree. And linear power supplies as well. There are good, bad and ugly there as well.
 
I don't have much time today. Short answer: Yes, it's repeatable. And the ferrite shows those little arrows, while I agree that it should be non-directional, but it is not.

That's the link to the cable: https://www.amazon.com/gp/product/B0CB4QBR73/

On Amazon it looks like the ferrite is attached to the end of the cable, but in fact it"s in the middle.

Screenshot 2024-06-15 at 5.53.39 PM.png
 
I think that the arrow is supposed to indicate the cable signal direction. The ferrite was just the best place for printing labels.
 
Interesting thread. When ferrits make a difference I find it strange, that it is not a standard for every cable, as It's that cheap.

So would you recommend to add ferrits at every power cable and analog signal cable at both ends when there is noise and hum?
 
Ferrites work above about 100 kilohertz.
They have nothing to do with power line hum & buzz.
And little to do with most noise.

Decades ago, some printers and desktop PC came with power cord ferrites.
 
Seems like the real lesson here is to use a touch of common sense and not set transformers (or any other dramatic EM field generators) directly on top of your analog interface cables.

Here's another test for you. Take the cable that performed the worst in the above testing and measure its performance at increasing distances from the EM fields, something like 1" away, 2" away, etc. I believe you'll quickly find out that a little bit of distance makes a massive difference.
Transformer caused hum in an interconnect is easily fixed with a small amount of distance.
 
Back
Top Bottom