Inductors in passive EQ

[ipagel]

Hi i am quite new to diy.
and was just looking for info or how different things work.

i am interested in the Passive Eq like pultec but do not understand how they work.

could someone point me in the right direction of some information/reading on this topic.

what i would like to know is how the passive eq works.
and what the inductors do.

thanks for any help.

 

[ioaudio]

check this:
http://home.online.no/~jaeioluf/sound/eqpassiv.htm
google for expressions you´re not sure off (or search for them here on the board)

 

[ipagel]

thanks thats very helpful. :thumb:

 

[rafafredd]

Have you seen it?

They say there are 144 inductors inside this thing... But saying that separate inductors for each frequency generates lower THD than a taped coil sounds like marketing BS to me... I don´t know.

 

[ipagel]

[quote author="rafafredd"]Have you seen it?

They say there are 144 inductors inside this thing... But saying that separate inductors for each frequency generates lower THD than a taped coil sounds like marketing BS to me... I don´t know.[/quote]

which thing thing Rafa

 

[rafafredd]

hahaha... forgot the link...

http://www.spl-usa.com/passeq/2595_inshort_E.html

 

[shabtek]

that thing is ridiculous! asthetically beautiful-- but that layout :shock:

they really talk it up too, the 72 coils per ch does not mean anything to me...never heard or seen one tho

 

[rafafredd]

Yeah... passive attack... why would separate inductors work better than a simple tapped one??? doesn´t make any sense at all!

 

[CJ]

you can wind the inductor in a more precise fashion if it is only to be used for a single band.
if you wind, say 1 1/2 layers on a toroid, you get distortion compared to 1 or 2 layers.
the flux will be cutting two layers on 50 percent of the core, and one layer on the other half, what do you think happens to distortion?

a tapped inductor will break up the mechanical symmetry if not designed so that each tap is represented by an integer value of layers.

 

[mickey76]

Interesting point CJ. Thanks.
I'm winding some inductors (first time I try this) for a pultec style eq. I use the cores from conrad.de that someone on the Lab recommended to me. They don't cost much so I wouldn't mind winding individual inductors as opposed to a single tapped one.
But to get an integer number of layers I'll have to deviate from the number of turns I calculated. How do you solve this. Just use another cap value to get close to the desired frequency with the new inductor value? Or can you use only part of the core? Maybe tape off some of it or something before you start winding? Does that have any adverse effects?
I think that might be the only possible solution. With only a limited number of core sizes and cap values available you'll never get the frequencies you aimed for. Or maybe I shouldn't be so fixated on those exact frequencies?

 

[bcarso]

The important thing with toroidal magnetics is the uniformity of distribution of the turns, particularly if you need to preserve the self-shielding characteristics.

 

[CJ]

mickey, are you winding toroids or ei bobbins? pt cores?

 

[mickey76]

it's a bobbin with a ferrite core that has to be glued together