Small values EQ inductors

For the REDD EQ I am designing I need some small value inductors - much smaller than you normally get in the readily obtained inductors from the likes of Carnhill. I am talking 12mH to about 48mH. I was wondering if any one had had any experience of using small leaded individual inductors in EQ circuits and how the compare to the more traditional  type? The sort of inductor I am looking are are ones like this:

http://uk.farnell.com/wurth-elektronik/744742223/inductor-power-22000uh-5-9x9mm/dp/2211726?in_merch=New%20Products

Cheers

Ian

depends on the freq response you want,

typically, those mini coils have a lot of high end roll off,

small wire is used, many turns close together=stray C,

however, this can be in the 100 khz range or 1 mega-hz range,

which may be well past the freq you want to control,

you can roll your own on a chunk o ferrite and get better response if needed,

just space out the turns more,

now if you wanna get hi-tech, you can include Q into the equation, DCR vs Henries,

this is don's best tune, tell me what you think, G with a cool Em bridge, Ferguson #1

http://www.youtube.com/watch?v=26PoK-njqL8

If you are using inductors of this small values in an EQ, it points towards being run at very-low impedances.

This would make series resistance and current capabilities important factors.

Going this route, I've had very good results with common mode line filter chokes, e.g.: http://uk.farnell.com/wurth-elektronik/7446121010/choke-common-mode-10mh-0-7a/dp/1748629

These filter chokes are available from ca. 2x0.5 to 2x100mH - and being dual-coils on same toroid, you can quadruple inductance by series-connecting the two coils.

Jakob E.

gyraf said:

If you are using inductors of this small values in an EQ, it points towards being run at very-low impedances.

This would make series resistance and current capabilities important factors.

Going this route, I've had very good results with common mode line filter chokes, e.g.: http://uk.farnell.com/wurth-elektronik/7446121010/choke-common-mode-10mh-0-7a/dp/1748629

These filter chokes are available from ca. 2x0.5 to 2x100mH - and being dual-coils on same toroid, you can quadruple inductance by series-connecting the two coils.

Jakob E.

Click to expand...

Thanks for the pointer Jakob. In this instance the impedance is not that low but the Q is very low, hence the low inductance values. The characteristic impedance at resonance is around 750 ohms. These common mode chokes certainly look meaty enough - it's a pity their tolerance is only 30%.

Cheers

Ian

Ian,
I made a Pultec using similar coils and it worked perfectly.
Farnell didn't do them at the time so I bought a complete range of them from this company:-
http://www.jabdog.com/

best
Davep

ruffrecords said:

For the REDD EQ I am designing I need some small value inductors - much smaller than you normally get in the readily obtained inductors from the likes of Carnhill. I am talking 12mH to about 48mH. I was wondering if any one had had any experience of using small leaded individual inductors in EQ circuits and how the compare to the more traditional  type?

Click to expand...

  The specs look good, with SRF well outside audio range and low DCR and very little inductance variation vs. level.
If you carry on experimenting with those, I'll be interested in your results.
What inductance vs. center frequency are you targetting?

abbey road d enfer said:

ruffrecords said:

For the REDD EQ I am designing I need some small value inductors - much smaller than you normally get in the readily obtained inductors from the likes of Carnhill. I am talking 12mH to about 48mH. I was wondering if any one had had any experience of using small leaded individual inductors in EQ circuits and how the compare to the more traditional  type?

Click to expand...

  The specs look good, with SRF well outside audio range and low DCR and very little inductance variation vs. level.
If you carry on experimenting with those, I'll be interested in your results.
What inductance vs. center frequency are you targetting?

Click to expand...

The small value inductors are needed for the 'brilliance cut. The Q circuit Q is less than 1. For 10KHz I need 12mH. The part of the circuit I am considering them for is at the bottom right of this circuit:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MKIIV2circuitscaled.jpg

Cheers

Ian

ruffrecords said:

The small value inductors are needed for the 'brilliance cut. The Q circuit Q is less than 1. For 10KHz I need 12mH. The part of the circuit I am considering them for is at the bottom right of this circuit:

Click to expand...

I can't see any reason why it wouldn't work there; you may have to alter the values of the resistor chain if you're critical about the accuracy of the cut's amplitude, that's all.

abbey road d enfer said:

ruffrecords said:

The small value inductors are needed for the 'brilliance cut. The Q circuit Q is less than 1. For 10KHz I need 12mH. The part of the circuit I am considering them for is at the bottom right of this circuit:

Click to expand...

I can't see any reason why it wouldn't work there; you may have to alter the values of the resistor chain if you're critical about the accuracy of the cut's amplitude, that's all.

Click to expand...

The Q of the example 22mH at the frequency it used at of 4.7KHz works out at about 11.8. Since the circuit Q is one tenth of this then hopefully the resistor chain will not need much altering. I think I need to buy some and try them out.

Cheers

Ian

ruffrecords said:

The Q of the example 22mH at the frequency it used at of 4.7KHz works out at about 11.8. Since the circuit Q is one tenth of this then hopefully the resistor chain will not need much altering. I think I need to buy some and try them out.

Click to expand...

Q is not a concern, the ampliude of the cut may be one. DCR needs some attention because it is probably higher than the original coil, particularly if you intend to use several in series.

abbey road d enfer said:

ruffrecords said:

The Q of the example 22mH at the frequency it used at of 4.7KHz works out at about 11.8. Since the circuit Q is one tenth of this then hopefully the resistor chain will not need much altering. I think I need to buy some and try them out.

Click to expand...

Q is not a concern, the ampliude of the cut may be one. DCR needs some attention because it is probably higher than the original coil, particularly if you intend to use several in series.

Click to expand...

Yes you are right. I checked the simulations and I had set the DCR to just 10 ohms which is too low for these inductors.

Cheers

Ian