Ferrite beads on hifi cables

[admin_exported]

I was wondering why ferrite beads are never used on hifi cables. Would they not help reduce EMI/RFI noise?

 

[Anonymous]

You mean on the mains cables? I'm no electrician but wouldn't adding them to audio cables restrict some of the frequencies getting through?

 

[Anonymous]

Yes mains cables but I'm not sure if they affect high frequencies in interconnects and speaker cables as you suggest. I'm hoping someone can explain because I'm wondering if the ferrite beads that clip on to cables would make any sort of improvement.

 

[Tony_R]

The point of ferrite beads is to reduce HF interference, by creating an inductor along the cable.

So in essence, with enough inductance (and it won't take much) you will end up rolling off the high frequencies, which to some may sound better...

So in conclusion I would say that it's a bad idea.

Tony.

 

[Anonymous]

Okay but what about mains cables?

 

[Tony_R]

It's usually a good idea with mains cables.

For a CD player / DAB tuner I would place them close to the device.

For an amp I would place a couple along the lead, starting from the plug.

CD players and DAB devices can generate noise, which can find it's way on to the mains cable by way of internal radiation (although probably at minute levels) but it can't do any harm to put beads on.

How big are the beads you have?

Tony.

 

[Anonymous]

Hi Tony,

I have two of these TDK ones:

They accept cable up to 9mm although you can buy them for different sizes. 9mm fit my mains cables fine so I'll have to get some more.

Thanks.

 

[Tony_R]

They look pretty standard - seen quite a few of those on computer mains leads.

They'll certainly help to reduce EMI/RFI (they can't do any harm anyway - unless you drop one on your toe!!)

Tony.

 

[chebby]

What fresh madness is this?

 

[nads]

chebby:What fresh madness is this? Not fresh, some electronics producers provide them to add to your power lead for their kit so that they can comply with X or Y regulations.

 

[Tony_R]

chebby:What fresh madness is this?

It's commonplace in the computer industry to have devices such as this on the power leads, although these days most PSU's have a significant amount of EMI filtering built into the IEC socket.

This serves to reduce the amount of RFI emanating from the switched mode PSU - to enable them to comply with regulations.

And incidentally, these filtered sockets make ideal modifications for most hifi equipment... I know because I have scavenged a few... (I work in the computer industry in case you hadn't already gathered!).

So it's no fresh madness - the theory applied is in fact identical to that as used in most filtered mains distribution units.

Tony.

 

[Tony_R]

chebby:So I assume the manufacturers are qualified to fit the requisite devices/filtering or whatever inside their electronics or (as you say) into their power leads where required.

Given that my mains cable is shielded (as is the Tacima cable also) and given that manufacturers are also aware of the problems of EMF/RFI, why do I need to festoon all my power leads with little iron doughnuts? (Just in case they missed one?)

Chebby, I think the primary discussion here is revolving around "untreated" (couldn't think of a better word) mains cable(s).

Even today, not much low to medium end HiFi equipment has any significant amount of supression that I'm aware off.

Think cars - and back to the 60's and 70's when very few cars had factory fitted interference supression (filtering by another word) - and one method was to fit a resistor in series with the plug lead(s). But for many years it has been mandatory, and was solved by leads of carbon / silicon construction (amongst others).

I realise this is a bit off topic, but I'm trying to make a point...

It's only equipment with switched mode PSU's that has a mandatory requirement for certain noise levels radiating *out* of the PSU on to the mains, and hence that's where you will find some kind of filtering.

Tony.

 

[chebby]

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[chebby]

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