Permeability of MPP core, would this work?

[Signalglow]

Hi,
I am going to wind a toroid inductor for this circuit,
but would a high permeability core of this type have any downsides?
And is 34 AWG wire fine for this?

Info on core:
Core type MPP
OD 39.90 mm
ID 24.1 mm
HT 14.5 mm
AL value: 740 +/- 8% (nH)
MPP Permeability: 550 (μ)
Wire gauge: 34 AWG

Turns:
16 KHz - 29.9 mH 195 turns
10 kHz - 31.4 mH add 5 turns
8 kHz - 48.2 mH add 48 turns
5 kHz - 67.5 mH add 45 turns
4 kHz - 87.9 mH add 41 turns
3 kHz - 156 mH add 111 turns

Help is much appreciated!

 

[rjenkinsgb]

I don't see a problem, though admittedly it's a few decades since wound any audio inductors and then I always used pot cores..

If you were using cores for power handling / power transformers then a lot of other factors come in to play, but for low level audio it should be OK.

If you are unsure, just wind one first and try that in your circuit.

That's generally a good idea anyway, whether you considers it just good practice or "Murphy's Law" - if you don't start testing something until it's totally finished, you are far more likely to find a major problem that means taking it apart again

 

[dr pepper]

I had a peavey deuce amp that had an equalizer that used chokes.

A high u choke ought to be Ok, this kind of choke has a sharp knee on saturation, but its very unlikely you'll drive it that hard.
You can build an op amp choke simulator, a gyrator.

 

[Signalglow]

Thanks for clearing this up for me guys.

All the best.

 

[JimB]

I did some quick calculations, and I get different numbers of turns for the inductance values that you require.
Not wildly different, but 10 or 20% (ish).

On a practical note,
how many toroids have you wound with 34AWG wire?
how many toroids have you wound with 445 turns and 5 taps?
do you have a toroid winding machine?

I suggest that this is not an easy task.

JimB

 

[Signalglow]

I did some quick calculations, and I get different numbers of turns for the inductance values that you require.
Not wildly different, but 10 or 20% (ish).

On a practical note,
how many toroids have you wound with 34AWG wire?
how many toroids have you wound with 445 turns and 5 taps?
do you have a toroid winding machine?

I suggest that this is not an easy task.

JimB

Hi JimB,
Thanks for your reply.

I have never wound a toroid coil before..
I know this is a little crazy to do by hand, but i only need one coil.

To be honest i do not even know if 34 AWG would suit this, or if i should go lower on the scale
to get a lower resistance in the wire.
I used this calculator LINK

I forgot to mention that i have ordered an MPP core with 125u instead, because 550u would not work with the required frequency range.

The other problem is that, to get the best results winding these (low parasitic capacitance) i would have to wind these in a special way using the progressive winding technique
i have a little knowledge about how to use this technique in the moment, but any tips would be appreciated a lot.

Thanks again!

 

[gophert]

The 34 gauge wire will allow a single layer of wire on the inside if the ring. 30-gauge will require doubling up the windings on the inside of the ring. I have never seen anyone make that many wraps by hand without breaking the wire. You inevitability get a kink in the wire and that makes a weak point that eventually breaks.

 

[Signalglow]

Well just calculated this, and i need 924 turns in total, have to give it a go now i guess.
Yes its pretty mad, i think you are right it will fail at some point, doing this by hand.

 

[gophert]

Well just calculated this, and i need 924 turns in total, have to give it a go now i guess.
Yes its pretty mad, i think you are right it will fail at some point, doing this by hand.

Pay attention to your total DC resistance of a piece of thin wire that long. DC resistance can change your resonance frequency.

 

[Signalglow]

Pay attention to your total DC resistance of a piece of thin wire that long. DC resistance can change your resonance frequency.

Okay this would then be 44m i need in total (extra meter for the taps)
That is 37 ohm DC resistance,
If i go with a 30 AWG wire that would be 15 ohm.

I do not really know if i should go with 30 AWG instead.
I could imagine that it would be easier to wind with a thicker wire. but as you say it would use more space on the core.

Updated specs.

Core type MPP
OD 39.90 mm
ID 24.1 mm
HT 14.5 mm
AL value: 168 +/- 8% (nH)
MPP Permeability: 125 (μ)
Wire gauge: 34 AWG

16 KHz - 29.9 mH 409 turns
10 kHz - 31.4 mH add 10 turns
8 kHz - 48.2 mH add 100 turns
5 kHz - 67.5 mH add 95 turns
4 kHz - 87.9 mH add 186 turns
3 kHz - 156 mH add 134 turns