I've got a D-AMP, how to build my inductor ? - diyAudio
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Old 3rd October 2007, 02:29 PM   #1
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Default I've got a D-AMP, how to build my inductor ?

Hi !!

I bought from Digikey, 6 TDA8920BJ IC's.

It needs a 22uH + 680nF output filter to work with 4Ohms load, and 47uH + 330nF to work with 8 Ohms. Question... Why does it need different output filters to work with different loads? It isn't just a low pass filter to take PWM signal away from the speaker

Well ! I REALLY want to hear this little thing, It's my first D amp, and I'm quite excited ! I can't get inductor easily around here, so I want to build my own. I have here on the shelf a enlammed copper wire 18AWG, and a bunch of old computer PSUs. Can I make my inductor from this? What about an aircore inductor, does it sounds better ? I also can buy ferrite core, and wind in myself, and of course, to buy it I must know the size that I don't have any idea yet !

Thank you so much !!!!!


Best Regards !
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Old 3rd October 2007, 02:51 PM   #2
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For Tube style airCore, I remember...

L [nH] = ( Turns x TubeDiaMeter[mm] )^2 / Length[mm]

example,
(200 turns x 5mm diameter)^2 / 10mm length = 100uH

anyway very large but no core distortion.
(sorry first equation had mistake)
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Old 3rd October 2007, 03:01 PM   #3
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Very VERY large you mean ! For 47uH it would need > 2000 turns

I need calculate it for ferrite core !

This would work fine for me:

http://uk.farnell.com/jsp/Passive+Co...sp?sku=1077056

BUT... I live in brazil, the land of corruption, and this sh**T costs 26 reais, 13usd... Ridiculous for a simple inductor, and I need two for each amp. !
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Old 3rd October 2007, 04:34 PM   #4
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I found a Store that have everything to make inductors, many types of ferrite, and all sizes of copper wire.

I need some technical information before go there and buy these components. Which ferrite former is better?

The amp works with +/- 27v, and is 2 Ohms compatible. What is the recommended current rating for the inductor ?

Thank you very much !
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Old 3rd October 2007, 05:43 PM   #5
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First attempt ! How does it look like? Is it good?

Hehehehehe just a joke !

Apart of this, I really need help regarding this !!!
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Old 3rd October 2007, 06:24 PM   #6
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Sorry I can't answer your questions, but here is a very handy calculator for ferrite and iron powder cores.......

http://www.66pacific.com/calculators/toroid_calc.aspx
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Old 3rd October 2007, 09:47 PM   #7
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I couldn't wait for an answer, and I went to the store and bought some ferrite cores. They were VERY cheap. I just finishied winding it right now, and here is the picture of the inductor.

The wire is 18AWG, 28 turns, how much uH do you guys think that it have?

Thank you !
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Old 3rd October 2007, 10:38 PM   #8
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Quote:
Originally posted by -_nando-_
I couldn't wait for an answer, and I went to the store and bought some ferrite cores. They were VERY cheap. I just finishied winding it right now, and here is the picture of the inductor.

The wire is 18AWG, 28 turns, how much uH do you guys think that it have?

Thank you !
You must know material type and size to calculate the inductance.

If these are ferrite toroids (0.9 inches?) you get 1000uH (1mH) with material 68, that has low permeability (20) and about 35mH (35000uH) if material type is 43 (850 perm).....

I don't think this is the right material for the application.

Take T106 Iron Powder cores with low perm. The red type (perm 10) needs 59 turns of wire to get 47uH. If you use 20AWG the turns will fit in a single layer.
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Old 3rd October 2007, 11:48 PM   #9
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I also have two ferrite cores, one is type 62 and other is 49. The Type 62 is bigger, and have a hole diameter of 15mm and 5mm of lenght.

The type 49 have a hole diameter of 13mm and 10mm of lenght.

I'm not sure about the ferrite types, so I took a picture of it, as it was difficult to read I wrote using mspaint what is marked on it.

Take a look:
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Old 3rd October 2007, 11:49 PM   #10
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the other
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