identifying Ferrite bead value? - Page 1
Forum section: electronics / beginners

author: samholloway
author_rank: Newbie
timestamp: May 06, 2024, 04:19:43 am
content: HI there guyshow do you know the component value of a ferrite Bead?I have one blown on a PCB for Fender Rumble 200 PreampThere is an old thread on this topic but its nearly 8 years old so not holding hope of a reply.any help would be greatly appreciated.!

author: jonpaul
author_rank: Super Contributor
timestamp: May 06, 2024, 04:58:10 am
content: select from Fair-Rite/TDK, EPCOS etc by the size and shape.Just jump a wire for now, you will see no difference in the soundJon

author: Konkedout
author_rank: Frequent Contributor
timestamp: May 06, 2024, 05:18:59 am
content: This is a difficult question. I think ferrite beads are generally unmarked.What do you mean by "blown"? Is it physically damaged? I don't think a ferrite bead will go bad unless it is physically damaged.They are made of different ferrites so even with fixed dimensions, different types can exhibit different characteristics.I am not certain why an audio preamp would have a ferrite bead. One possible explanation is to reduce sensitivity to radio frequency fields. I had an amateur radio license and a single sideband transmitter when I was young. Our living room stereo audio equipment would produce loud garbled audio if it was operating while my transmitter was transmitting. This falls into the broad category of Electro Magnetic Compatibility (EMC).

author: samholloway
author_rank: Newbie
timestamp: May 06, 2024, 05:51:26 am
content: HI, its blown, as in there's a small viable hole in the component. God knows how that occured.I believe its for HF interference.

author: samholloway
author_rank: Newbie
timestamp: May 06, 2024, 05:52:47 am
content: Quote from: jonpaul on May 06, 2024, 04:58:10 amas in remove the blown ferrite and just solder a wire in it's place?

author: jonpaul
author_rank: Super Contributor
timestamp: May 06, 2024, 06:14:21 am
content: The bead issue is a symptom and not the cause of your issues.check for short circuit or voerloand on DC power.Can you please add photos of the bead and blown via.Jon

author: radiolistener
author_rank: Super Contributor
timestamp: May 06, 2024, 06:37:13 am
content: Quote from: Konkedout on May 06, 2024, 05:18:59 amIt can, if you apply to much AC power, it leads to saturation and too much heating which destroy core material

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2024, 06:41:55 am
content: Quote from: Konkedout on May 06, 2024, 05:18:59 amThey can be overheated under extreme conditions.QuoteIt could be that, or to suppress local oscillation.

author: samholloway
author_rank: Newbie
timestamp: May 06, 2024, 12:30:57 pm
content: Quote from: jonpaul on May 06, 2024, 06:14:21 am

author: radiolistener
author_rank: Super Contributor
timestamp: May 06, 2024, 04:38:37 pm
content: looks like it happens due to overcurrent, most of all it happens due short circuit which may happens due to broken mosfet for example. So, if you replace it, the new one also will be burned. You're needs to fix the root of cause.

author: samholloway
author_rank: Newbie
timestamp: May 07, 2024, 03:16:00 am
content: Well i removed the burnt out ferrite bead and replaced with a piece of wire and it works perfectly now. lolno issues. I have bought another board just in case as a spare but it seems to work fine for now.Thanks

author: MathWizard
author_rank: Super Contributor
timestamp: May 07, 2024, 02:31:44 pm
content: Do you mean a ring type Ferrite bead that goes on the through-hole pin of some transistor, or do you mean it was that SMD thing in the pic ? Was it just an inductor ?I'd make a map of the circuit, figure or find a likely value, and just order some SMD inductors, even from amazon or ebay.But too late now.

author: CaptDon
author_rank: Super Contributor
timestamp: May 07, 2024, 08:25:39 pm
content: That ferrite bead is so small that the inductance is nearly meaningless for audio frequencies, probably marginally effective at less than 100MHz. I think Fender put it there to suppress radiated emissions. Jump it with a wire and you'll never miss it.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 08, 2024, 09:19:53 am
content: I looked at several datasheets of some ferrite beards and measres several of tgem with an RLC meter an ca say they typically have inductance about 1 uH (or a bit less). So, I guess for audio equipment any similar size (and current) ferrite beard will do the job.(I guess its job is pretty simple - being a bit inductive wire).

author: David Hess
author_rank: Super Contributor
timestamp: May 08, 2024, 01:58:43 pm
content: Quote from: Vovk_Z on May 08, 2024, 09:19:53 amThe ferrite bead does not add just a bit of inductance. What is important is that it is lossy at the frequency of interest, so it acts like a resistor at higher frequencies but with zero resistance at DC. It is equivalent to an inductor in parallel with a low value resistor, so at DC the inductor provides zero DC resistance, and at higher frequencies the low value of parallel resistance dominates over the inductive reactance.