Ferrite beads
Mar 9, 2006 at 4:59 AM Thread Starter Post #1 of 7

Xakepa

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I have ferrite bead molded on both ends of my soundcard cable.

Do they have any impact on the (analog audio) signal, and is there a benefit to put 'em here and there...say on the PSU cable?

10x
 
Mar 9, 2006 at 5:10 AM Post #2 of 7

ericj

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A ferrite bead is an inductive device that is typically most reactive at high frequencies.

What this means is that really high frequency stuff - like RF interference - experiences a high impedance at the bead.

On the output of a feedback amplifier, it can strip ultrasonic noise that might otherwise enter the feedback loop and cause the amplifier to oscillate or otherwise misbehave.

Remember that the output wire is also a receiving antenna unless great care has been taken to shield both the signal and ground lines.

It is more or less guaranteed not to have a measurable or noticible negative effect on sound quality. It's all good.

On the input or power rails of an amplifier, it serves to strip out RFI and EMI that might enter the circuit through those vectors.

Since this is inside the computer, i can almost guarantee you that there is a big fat ferrite bead on the lines from the IEC inlet in the power supply, followed by a common-mode choke on the board, so sticking a big bead on the power cable will do approximately nothing.
 
Mar 9, 2006 at 7:54 PM Post #3 of 7

mono

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Quote:

Originally Posted by ericj
Since this is inside the computer, i can almost guarantee you that there is a big fat ferrite bead on the lines from the IEC inlet in the power supply, followed by a common-mode choke on the board, so sticking a big bead on the power cable will do approximately nothing.



You'd be surprised, it is extremely common to not have a big fat ferrite bead in the PSU, and common enough to not have a choke on the board in lower-end PSU. Better PSU will have them but looking at a % of systems, most don't have better PSU inside excepting good OEMs.
 
Mar 9, 2006 at 10:48 PM Post #4 of 7

Xakepa

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I was actually talking about the noise on the power line from the wallwart to my amp (there's a "drop-in" 7824 inside).

I put the bead right next to the power connector, and my rational is to keep HF away from power rails and virtual groud.

Mu computer PSU is pretty good, Fortron 350W AFAIR, so I'm not concerned about that.

580smile.gif
 
Mar 9, 2006 at 11:20 PM Post #5 of 7

Garbz

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The best powersupply on your computer is horrible for audio purposes
tongue.gif


Ferrite beads as stated block RFI and the sort. It'd be more inclined to put a ferrite bead on the output of the regulator to kill any regulator induced HF noise too.
 
Mar 9, 2006 at 11:58 PM Post #6 of 7

mono

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Quote:

Originally Posted by Xakepa
I was actually talking about the noise on the power line from the wallwart to my amp (there's a "drop-in" 7824 inside).

I put the bead right next to the power connector, and my rational is to keep HF away from power rails and virtual groud.

Mu computer PSU is pretty good, Fortron 350W AFAIR, so I'm not concerned about that.

580smile.gif



This sound card cable, is it meant for inside the computer? Environment plays a role in noise pickup, if you don't have the noise to deal with, you don't need it. Switching supplies often have one on the cord but they have more HF noise inherant in their design.

If you want one, go ahead and try it, but which is the more "common" part in the equipment chain, the amp or the supply? What I'm getting at is if the amp is more likely used with alternate supplies, put the ferrite on the power line of, inside the amp. If the supply is more likely used with other amps, put it on the supply cord just prior to the amp. I suppose you could just put them everywhere but until there's a demonstrated need or benefit...
 
Mar 10, 2006 at 9:11 PM Post #7 of 7

Xakepa

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Quote:

Originally Posted by mono
This sound card cable, is it meant for inside the computer? Environment plays a role in noise pickup, if you don't have the noise to deal with, you don't need it. Switching supplies often have one on the cord but they have more HF noise inherant in their design.

If you want one, go ahead and try it, but which is the more "common" part in the equipment chain, the amp or the supply? What I'm getting at is if the amp is more likely used with alternate supplies, put the ferrite on the power line of, inside the amp. If the supply is more likely used with other amps, put it on the supply cord just prior to the amp. I suppose you could just put them everywhere but until there's a demonstrated need or benefit...



Sound cable is designed to run outside, from the SC to some old 5.1 Altec Lansing's I discarded long time ago. It does have beads on both ends, supposedly to eliminate RF pick-up making it's way into (integraded) amp inside the speakers...or the SC

PIMETA is (allways) powered by 30V wallwart, and there's "drop-in" 7824 in the enclosure. I have no room for a bead insisde. I mounted the bead next to the output plug of the wallwart (i.e.before the amp) , preventing power cord (wallwart-amp) pick-up from making it to 7824->power rails and virtual ground.

I see no reason no put any more beads, and I'm concerned with RF noise. 50Hz noise on the ground wire though is a different story.
 

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