You cannot trust the color code on the core. I have seen some large differences between some cores of the same color.
The best thing to do if you have a laptop or PC of some sort is learn to measure inductance using a signal source and either a voltmeter or scope.
You can find oscilloscope software along with signal generator software that can be used instead of buying test equipment.
If you are raiding power supplies, you want to look for the common mode choke in the line side. Those will likely match your needs. The actual pulse-power cores will be a low permeability types and need lots of turns to work.
The best thing to do if you have a laptop or PC of some sort is learn to measure inductance using a signal source and either a voltmeter or scope.
You can find oscilloscope software along with signal generator software that can be used instead of buying test equipment.
If you are raiding power supplies, you want to look for the common mode choke in the line side. Those will likely match your needs. The actual pulse-power cores will be a low permeability types and need lots of turns to work.
Ferrite (nickel zinc) 16–640
Iron (99.8% pure) 5000
Nanoperm 80000
Permalloy 8000
Good ribbon mikes did not happen before Alnico and Permalloy.
(Commercial Iron tends to run near 1000, not the 5000 lab number.)
The simple Ferrites are not even in the running.
Some of the super-modern ferrites may be, but can't be sourced in small lots.
What about
https://www.surplussales.com//Inductors/FerToro/FerToro-3.html
Toroid. Tape core wound. 0.900" inside diameter, 1.483" outside diameter, 0.470" high. Alt. P/N: 44E4602.
https://www.surplussales.com//Inductors/FerToro/FerToro-3.html
Toroid. Tape core wound. 0.900" inside diameter, 1.483" outside diameter, 0.470" high. Alt. P/N: 44E4602.
$2.50 each
No need for super-ferrites: ordinary low frequency, MnZn ferrites routinely exceed, 10,000:
https://www.tdk-electronics.tdk.com...os-ferrites-and-accessories/ferrite-materialsThey are used for transformers, CMC, etc and are very cheap and easily available
It depends. I once wound a 50 turns current transformer toroid for audio measurements - and used the material with highest permeabiltiy available, Nanoperm from Vacuumschmelze - achieving a low frequency cutoff in the ballpark of 20Hz. No way to come close with any ferrite here.
Btw, my company payed about 500€ for the lot of 25 toroids, that's why we called it "EMC-jewelry"
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Sure, but what I mean is that ferrites are not limited to NiZn (HF VHF), and their µi easily matches or exceeds ordinary silicon steel. Dedicated materials or alloys do much better of course
True, but sat level of steel reaches 2T whereas Ferrite ends at 0.4T. Once I designed an 1:1 audio transformer for a POTS-interface using a ferrite pot core. Yes, it could be done, but required a bunch of equalization to meet requirements in the 300~3400Hz telephony range.
Saturation matters when high induction levels are involved: power, DC bias, etc. but for a mic transformer it is essentially irrelevant. µi and hysteresis are paramount though
I had a quick look in Mouser for a suitable sized nano crystalline toroid. I found a Hitachi one 16mm x 13mm x 6.2mm the FT-3K50T F1613YS This uses Hitachi
Finemet material with T type annealing giving a flat permeability up to about 70Khz of 50000 which is higher than any ferrite I know. The quoted Al at 10Khz is 10uh
so to get 780mh, which I think was the quoted neccessary inductance to get a reasonable LF you would need 280 turns if my numbers are correct.
This is with a very high permeability material so with lesser materials you will need even higher number of turns. I dont fancy trying to wind that number of turns on a tiny
toroid unless I had a special winding machine.
Sorry but I dont think you are going to get anything remotely useful out of trying to wind a few turns on some unknown ferrite material.
If I was seriously trying to do this I would use small nickel laminations.
Finemet material with T type annealing giving a flat permeability up to about 70Khz of 50000 which is higher than any ferrite I know. The quoted Al at 10Khz is 10uh
so to get 780mh, which I think was the quoted neccessary inductance to get a reasonable LF you would need 280 turns if my numbers are correct.
This is with a very high permeability material so with lesser materials you will need even higher number of turns. I dont fancy trying to wind that number of turns on a tiny
toroid unless I had a special winding machine.
Sorry but I dont think you are going to get anything remotely useful out of trying to wind a few turns on some unknown ferrite material.
If I was seriously trying to do this I would use small nickel laminations.
the absolute only reason i'm doing it is because it's been done, with far less consideration than i'm putting in it with (imo) pleasing results.
I'm not trying to make an amazing mic i just want a fun project and a resulting fun mic as a bonus. but thanks for the info!
I just dont see how you can possibly get anything like pleasing results with a few turns of wire around a ferrite toroid but of course you can do what you want for fun no problem.
If you want to build a reasonable mic transformer Ive got some spare small size 49% nickel lams with matching bobbins you can have, at least enough for a pair of transformers.
They would be bigger than ferrite toroids but more likely to work.
If you want to build a reasonable mic transformer Ive got some spare small size 49% nickel lams with matching bobbins you can have, at least enough for a pair of transformers.
They would be bigger than ferrite toroids but more likely to work.
Ok pm me your address and Ill send them on. Im in Oxford England. Last night I tried a basic test and I think you will need about 100 turns to get the required primary inductance (780mh ?).
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I have considered an active design, and since i'll have plenty of spare supplies, and i have a good selection of opamps laying around i might just make one as well, right now i'd like to take on the challenge of a transformer though, thanks for the suggestion!