saturation point from inductor?

[jonathan perez]

call me an idiot this morning, but i dont understand what this means....


"One thing that became obvious is that you could artificially get a more linear core material to have an offset, and in the easiest way. If we're always pumping current through the inductor, we can get any offset we like by just pumping more. If we were to put a second winding on a wah inductor, we could force DC through it from a current source circuit, which would force the "center" of the magnetic operation toward one or the other saturation points. Of course, this is not possible with a pre-wound and potted wah inductor, but is emminently feasible if you happen to wind your own. It's even more feasible if the inductor you use happens to have a second winding, like the Radio Shack transformer that is mentioned later. This secondary can just be hooked up and current fed through it. I intend to do this as as soon as I get some bench time. Note that I've been saying "current source". You can't just use a resistor, because transformer action would reflect this resistance into the inductance winding as a load and damp the resonant action of the inductor. The minimum you need is a transistor connected as a current source to keep from doing this."

how would this be wound? i cannot visualize it, for some reason. thank you!

jonathan perez

[R.G.]

You would take a magnetic core suitable for the inductor, and wind an inductor winding on it to make the correct inductance. You would then wind a second, independent winding. This would make it look like a transformer with two windings.

But the second winding is only to introduce a magnetic offset. This second winding is fed a DC current.

It's fed DC from a current source to prevent the current feeder from loading down the "primary" inductor winding  by transformer action.

[jonathan perez]

i get it. i noticed on the old inductors i got, there were 4 leads, each with a wire. NOW it makes sense, as to why they did that. thank you, RG!

[alextheian-alex]

interesting!  i had been experimenting with saturation and parallel resistance in transformer based phase splitters to bend the transfer function at the extremes of the B-H curve to produce second order harmonics instead of cancelling them... but i completely forgot about that project until now.  Never thought about usind the concept in a wah pedal though.  Could make for an interesting experiment.

[Paul Perry (Frostwave)]

It's fed DC from a current source to prevent the current feeder from loading down the "primary" inductor winding  by transformer action.

I would never have thought of that in 10*6  dog years...

[johngreene]

i get it. i noticed on the old inductors i got, there were 4 leads, each with a wire. NOW it makes sense, as to why they did that. thank you, RG!

Except that this is normally considered a 'bad' thing, so I think your 4 wire inductors are probably tapped inductors. Very useful for PA design and impedance matching.

--john

[kvb]

This second winding is fed a DC current . . . from a current source to prevent the current feeder from loading down the "primary" inductor winding  by transformer action.

I have been periodically looking into current sources to learn how to modify a wah that has a Radio Shack transformer as its inductor.

this is what I have looked at so far:  http://sound.westhost.com/ism.htm#intro    http://www.4qdtec.com/csm.html    http://en.wikipedia.org/wiki/Current_source

Even though I haven't built or tested a current source yet, may I ask -  How much current would be necessary to have an audible effect on the quality of wah produced by the inductor?

[QSQCaito]

It's like putting a magnet beside the core, right?? It produces nice effects, if it's too perfectly wound.. it doesn't sound.. there is a little difference, it's not :O.. it adds mojo :p