Wah Inductors and magnetism

[GBlekas]

Hi all,

I have been messing with wahs for quite awhile now and fairly quickly I realized how much influence the inductor had to the over all tone of the classic Vox or Cry Baby wahs.
So digging further I see an inductor is made of a  bunch of turns of wire around a non metallic core....yawn...LOL

This experiment has actually been a cross country experiment done in two different labs.
One is mine and the other is a guy that I have become very good friends with who goes by the name Joe Gagan.

Ok, the classic wah calls a 500 mH inductor and that is ok but why would they sound different being the same exact rating in Inductance?
The simple answer was they were not the same actual reading and they did vary!

I had some suspicions about the cores in the older vintage wahs not being as pure as say they are today.
By not being pure that might make the inductor act somewhat like one of those electro-magnet experiments we all did as kids but does that change anything if this is true?

Is there anything else about inductors that we have found other than their rating in Henries?
Well yes, even two 500 mH inductors vary in resistance but for today I will just be concerned with their reading in Henries.

OK So I take a Stack of Dimes inductor and read it to see exactly where it sits in terms of the "ideal" 500 mH
I give you EXHIBIT A   reading 520 mH



But I need to have the "ideal" or my head will fall off or something even worse like my Wah won't have it's Mojo! 

Exhibit B: reading with small magnet on top gets me down to 515 mH, which while good isn't "ideal" so ..........




Determined to get to 500 mH I break out a heavier magnet this time
Exhibit C: 



OK Great but can I go lower? (for what ever reason)
I give you Exhibit D:



So, in this group of experiments I prove you can end up with a range of 471-520 mH depending upon the magnetic content! 

Next up maybe we can measure vintage inductors to see what their actual inductance was.
I think this could help in getting a vintage wah tone out of modern parts perhaps.
I also realize there is more to a wah than the inductor but first things first.

Comments?

Regards,
George

[Joe Hart]

WOW! Have you tried a magnet on the inductor in the actual circuit? What was the change in sound?
-Joe Hart

[trjones1]

I taped a small magnet onto my inductor because I'd heard of the theories about it being the secret to the "holy grail" wah sound.  I didn't hear any difference.  If there was a difference it was too subtle for my ears.

I think the 500 mH for the inductor is just a general rule of thumb.  Getting your inductor down from 520 to 500 mH isn't going to turn your wah magic or something.

[John Lyons]

Cool stuff George. Go man go. Don't listen to that crack pot Gagan.  
The clips are dead but I heard this a while back and it did sound sweeter to my ears.

http://www.diystompboxes.com/smfforum/index.php?topic=55476.0

[trjones1]

That's an interesting thread.  The inductor I tried the magnet on was actually a Fulltone, so maybe that's why I didn't hear much difference.  I withdraw my skepticism.

[defaced]

Thinking out loud here, but if you were to take a screw, affix a magnet to it, and position it over the inductor, you could tune the inductance from the outside of the enclosure by turning the screw and changing the distance between the magnet and the inductor.  I know *nothing* about wah circuits, so I have no clue if a change of 50 mH is significant, but I could see with the right magnet (neodymium) you could probably cover a pretty good range from the inductors max reading and below.  

[John Lyons]

Thinking out loud here, but if you were to take a screw, affix a magnet to it, and position it over the inductor, you could tune the inductance from the outside of the enclosure by turning the screw and changing the distance between the magnet and the inductor.  I know *nothing* about wah circuits, so I have no clue if a change of 50 mH is significant, but I could see with the right magnet (neodymium) you could probably cover a pretty good range from the inductors max reading and below.  

That sounds like a fairly simple and cool thing to do.

[Paul Marossy]

I taped a small magnet onto my inductor because I'd heard of the theories about it being the secret to the "holy grail" wah sound.  I didn't hear any difference.  If there was a difference it was too subtle for my ears.

I think the 500 mH for the inductor is just a general rule of thumb.  Getting your inductor down from 520 to 500 mH isn't going to turn your wah magic or something.

I've tried a magnet, too. I came to the same conclusion. I also agree about the inductor. There's a lot more to it than just the inductor in a wah circuit.

[GBlekas]

This idea came about with the idea that the inductors used in the original Clyde McCoy had something special going on so what could have caused that happy little accident?
It had to be impurities in the core of the inductor. So if these impurities were metallic in nature the inductor would become a little like an electro magnet and this experiment proves that magnetism does affect the inductance value.

Do you hear a 50 mH difference?  I know below 500 mH makes for a weak/thin sounding wah so one very well might hear a 50 mH difference if it went into the less than 500 region.

What is the actual value of a Clyde McCoy wah inductor?  Anybody have one to check?

[GBlekas]

Thinking out loud here, but if you were to take a screw, affix a magnet to it, and position it over the inductor, you could tune the inductance from the outside of the enclosure by turning the screw and changing the distance between the magnet and the inductor.  I know *nothing* about wah circuits, so I have no clue if a change of 50 mH is significant, but I could see with the right magnet (neodymium) you could probably cover a pretty good range from the inductors max reading and below.  

Love that idea!   

[R.G.]

So digging further I see an inductor is made of a  bunch of turns of wire around a non metallic core....yawn...LOL

Well, not exactly. An inductor is made of ... any conductor. Any/every conductor has self-inductance as a consequence of the magnetic field which current flow creates around the wire. Winding the conductor into a loop concentrates the M-field inside the loop and cancels it between wires. This forms the resulting field into one which (mostly) runs through the center and around the outside. If you go through the math, you find that the inductance of N loops of wire is N² times the inductance of one loop with the same loop area and other dimensions.

And the core can be vacuum, air, or other gasses, a non-magnetic solid, diamagnetic, or ferromagnetic. If it's non magnetic, the core material does not affect the inductance; if it's conductive, it affects losses, but not the inductance. If it's ferromagnetic, it both increases losses and increases the inductance by the factor of the relative permeability of the material. Iron has a permeability in the 10s of thousands. Sintered ferromagnetic materials have permeabilities in the range of units of thousands. So
(1) an inductor is a conductor, which has self conductance
(2) a  coil of conductors makes for N² times the inductance of one loop
(3) the core material may be magnetic or not, but whether it's a ferromagnetic material or not makes a HUGE difference, not whether it's metallic or not.

Ok, the classic wah calls a 500 mH inductor and that is ok but why would they sound different being the same exact rating in Inductance?

Well, it's because even identical inductance coils have different
(1) wire resistances
(2) core losses
(3) B-H curves (that is, inductance per magnetic force)
(4) self capacitance
(5) core gap (which linearizes the B-H curve)
(6) core shape (which varies the shape of the  B-H curve under heavy MMF)
(7) amount of MMF and how far that drives the B-H curve into saturation

Then there's that thing where the inductances have a tolerance.

The simple answer was they were not the same actual reading and they did vary!

That is a simple answer, but there is much more to it, as above. The exact same inductor will give you different measurements for inductance when measured at different AC currents, DC currents, and frequencies being measured.

I had some suspicions about the cores in the older vintage wahs not being as pure as say they are today.

You don't have to have suspicions. When I did the first work on wah  cores, it was clear that they were made with a cheap and not very good ceramic ferrite core. There are many grades of ferrite, and some are more ideal at low MMF, high MMF, low/high frequencies, some are more/less gapped, etc. That's even without winding variations.

By not being pure that might make the inductor act somewhat like one of those electro-magnet experiments we all did as kids but does that change anything if this is true?

Yes.

Is there anything else about inductors that we have found other than their rating in Henries?
Well yes, even two 500 mH inductors vary in resistance but for today I will just be concerned with their reading in Henries.

See above for a more comprehensive list.

OK So I take a Stack of Dimes inductor and read it to see exactly where it sits in terms of the "ideal" 500 mH
I give you EXHIBIT A   reading 520 mH
But I need to have the "ideal" or my head will fall off or something even worse like my Wah won't have it's Mojo! 
Exhibit B: reading with small magnet on top gets me down to 515 mH, which while good isn't "ideal" so ..........
Determined to get to 500 mH I break out a heavier magnet this time
OK Great but can I go lower? (for what ever reason)
I give you Exhibit D:
So, in this group of experiments I prove you can end up with a range of 471-520 mH depending upon the magnetic content! 

Actually, you prove that you can affect the incremental permeability of a ferrite by forcing a "DC" magnetic field through it. This was the basis of the old "magnetic amplifiers". The effect is well known and documented. You could have done much the same thing, and over a wider range, by forcing a DC current through the winding.

Next up maybe we can measure vintage inductors to see what their actual inductance was.
I think this could help in getting a vintage wah tone out of modern parts perhaps.
I also realize there is more to a wah than the inductor but first things first.

There is more to a wah than an inductor. In fact, the frequency of the resonance varies as 1/2*pi*SQRT(L*C), so the frequency resonance changes only with the square root of the change in inductance. A change from 500 to 520mH is going to be imperceptible, just from the math.

I taped a small magnet onto my inductor because I'd heard of the theories about it being the secret to the "holy grail" wah sound.  I didn't hear any difference.  If there was a difference it was too subtle for my ears.

It depends on a lot of things, like how well the magnet pushed the BH magnetizing curve of that core toward saturation on one side or another, and how big the test signal is.

It bothers me that my initial measurements have passed into internet myth and legend.  

This idea came about with the idea that the inductors used in the original Clyde McCoy had something special going on so what could have caused that happy little accident?
It had to be impurities in the core of the inductor. So if these impurities were metallic in nature the inductor would become a little like an electro magnet and this experiment proves that magnetism does affect the inductance value.

Yep. I did the initial measurements that showed a change in harmonic content on a magic mojo inductor from a sine wave signal - that is, soft distortion in the inductor itself because of the magnetic conditions. I posted it on usenet before there was a world wide web.

The exact value of the inductor is of far less interest than the secondary stuff like resistance (and hence resonance Q), self capacitance, and B-H curve linearity.

[Paul Marossy]

There is more to a wah than an inductor. In fact, the frequency of the resonance varies as 1/2*pi*SQRT(L*C), so the frequency resonance changes only with the square root of the change in inductance. A change from 500 to 520mH is going to be imperceptible, just from the math.

That's what I keep telling people about the actual inductor value. However it's apparently next to impossible to convince people that the inductor is only a small part of the overall picture. It's only job is to make the circuit a resonant circuit.

OK, maybe you can make somewhat of an argument for different cores and stuff, but I have found that those are subtle differences which could easily be negated by changing other things in the circuit, like the "Q" resistor for example.

Once again, I submit that this is an area that is largely given over to pyschoacoustics.

[GBlekas]

So digging further I see an inductor is made of a  bunch of turns of wire around a non metallic core....yawn...LOL

Well, not exactly. An inductor is made of ... any conductor. Any/every conductor has self-inductance as a consequence of the magnetic field which current flow creates around the wire. Winding the conductor into a loop concentrates the M-field inside the loop and cancels it between wires. This forms the resulting field into one which (mostly) runs through the center and around the outside. If you go through the math, you find that the inductance of N loops of wire is N² times the inductance of one loop with the same loop area and other dimensions.

And the core can be vacuum, air, or other gasses, a non-magnetic solid, diamagnetic, or ferromagnetic. If it's non magnetic, the core material does not affect the inductance; if it's conductive, it affects losses, but not the inductance. If it's ferromagnetic, it both increases losses and increases the inductance by the factor of the relative permeability of the material. Iron has a permeability in the 10s of thousands. Sintered ferromagnetic materials have permeabilities in the range of units of thousands. So
(1) an inductor is a conductor, which has self conductance
(2) a  coil of conductors makes for N² times the inductance of one loop
(3) the core material may be magnetic or not, but whether it's a ferromagnetic material or not makes a HUGE difference, not whether it's metallic or not.

Ok, the classic wah calls a 500 mH inductor and that is ok but why would they sound different being the same exact rating in Inductance?

Well, it's because even identical inductance coils have different
(1) wire resistances
(2) core losses
(3) B-H curves (that is, inductance per magnetic force)
(4) self capacitance
(5) core gap (which linearizes the B-H curve)
(6) core shape (which varies the shape of the  B-H curve under heavy MMF)
(7) amount of MMF and how far that drives the B-H curve into saturation

Then there's that thing where the inductances have a tolerance.

The simple answer was they were not the same actual reading and they did vary!

That is a simple answer, but there is much more to it, as above. The exact same inductor will give you different measurements for inductance when measured at different AC currents, DC currents, and frequencies being measured.

I had some suspicions about the cores in the older vintage wahs not being as pure as say they are today.

You don't have to have suspicions. When I did the first work on wah  cores, it was clear that they were made with a cheap and not very good ceramic ferrite core. There are many grades of ferrite, and some are more ideal at low MMF, high MMF, low/high frequencies, some are more/less gapped, etc. That's even without winding variations.

By not being pure that might make the inductor act somewhat like one of those electro-magnet experiments we all did as kids but does that change anything if this is true?

Yes.

Is there anything else about inductors that we have found other than their rating in Henries?
Well yes, even two 500 mH inductors vary in resistance but for today I will just be concerned with their reading in Henries.

See above for a more comprehensive list.

OK So I take a Stack of Dimes inductor and read it to see exactly where it sits in terms of the "ideal" 500 mH
I give you EXHIBIT A   reading 520 mH
But I need to have the "ideal" or my head will fall off or something even worse like my Wah won't have it's Mojo! 
Exhibit B: reading with small magnet on top gets me down to 515 mH, which while good isn't "ideal" so ..........
Determined to get to 500 mH I break out a heavier magnet this time
OK Great but can I go lower? (for what ever reason)
I give you Exhibit D:
So, in this group of experiments I prove you can end up with a range of 471-520 mH depending upon the magnetic content! 

Actually, you prove that you can affect the incremental permeability of a ferrite by forcing a "DC" magnetic field through it. This was the basis of the old "magnetic amplifiers". The effect is well known and documented. You could have done much the same thing, and over a wider range, by forcing a DC current through the winding.

Next up maybe we can measure vintage inductors to see what their actual inductance was.
I think this could help in getting a vintage wah tone out of modern parts perhaps.
I also realize there is more to a wah than the inductor but first things first.

There is more to a wah than an inductor. In fact, the frequency of the resonance varies as 1/2*pi*SQRT(L*C), so the frequency resonance changes only with the square root of the change in inductance. A change from 500 to 520mH is going to be imperceptible, just from the math.

I taped a small magnet onto my inductor because I'd heard of the theories about it being the secret to the "holy grail" wah sound.  I didn't hear any difference.  If there was a difference it was too subtle for my ears.

It depends on a lot of things, like how well the magnet pushed the BH magnetizing curve of that core toward saturation on one side or another, and how big the test signal is.

It bothers me that my initial measurements have passed into internet myth and legend.  

This idea came about with the idea that the inductors used in the original Clyde McCoy had something special going on so what could have caused that happy little accident?
It had to be impurities in the core of the inductor. So if these impurities were metallic in nature the inductor would become a little like an electro magnet and this experiment proves that magnetism does affect the inductance value.

Yep. I did the initial measurements that showed a change in harmonic content on a magic mojo inductor from a sine wave signal - that is, soft distortion in the inductor itself because of the magnetic conditions. I posted it on usenet before there was a world wide web.

The exact value of the inductor is of far less interest than the secondary stuff like resistance (and hence resonance Q), self capacitance, and B-H curve linearity.

Thanks for posting RG!

Without getting into the full what effects what of a wah I was trying to stick to just the inductor for now.
Reason being I have an old Jen wah with a film can inductor in it and it really is missing something even though all parts have been spec'ed out by me.
By spec'ed out I used all values from a great sounding Clyde McCoy that I reverse engineered.
OK, so the pedal just lacks sweetness and I know it's the inductor and will post measurements/pix soon.

Well we did a few readings back in December of various Inductors.
Reading mH's and resistance for comparison purposes.

I am not sure how to test the 2-7 that you mention above but I am trying to make sense of it all none-the-less...





One thing I have noticed is ohms and mH's do matter. 1 Henry, for instance, might be good for fooling around at home but certainly not in a band mix.
Anyway, I have my preferences here but that 500 mH "ideal" does vary as seen in above pix.

My '500' film can that lacks sweetness I read late last night and it was in the 450 mH range and while that works it doesn't work for my ear thus the magnet mod idea.
Ideally we can up range that 450 mH to 500 or slightly higher....but my test only prove, so far, that I can down range the inductance.

In the past I found the magnet appears to smooth the highs in a nice way and probably read it years ago from something you wrote.
So, you planted the seed and it's been festering with Gagan and me for years now....

Is there an easy way to up-range an inductor? Is it even possible to do?  I am thinking to reverse the magnet polarity or maybe two same pole magnets facing each other with the inductor sandwiched in between.  I am a man on a mission here because I want that vintage Jen wah to sound right! :>)

Thanks again for your input...I will print it out and let it fester in my frontal lobes...

[Joe Hart]

Could you take a small value inductor and run it in series with the existing one to "up" the inductance?
-Joe Hart

[GBlekas]

Here is the resonant frequency comparisons between a Jen wahs, one with a Fasel and the other with the film can.
The third is the SOD inductor along with how that is/was affected by the introduction of a pair of magnets.



The introduction of the magnet affected the inductor's mH's and Capacitance but not the resistance.




Here is how repelling magnets affected the capacitance of the inductor.


So all being said the number for the crappy sounding film can don't jive with the other known good inductors.

Here is my unproven/tested theory ...to be put to the test tomorrow....
All I have to do is add a resistor in series with the inductor to get the film can number to jive with the others.
Here is the proof in numbers



Will let you know if this pans out or not...time for bed ...

Regards,
George

[GBlekas]

Could you take a small value inductor and run it in series with the existing one to "up" the inductance?
-Joe Hart

Hi Joe,

If you take two identical  500 mH inductors with a Capacitance of 5 uf each and 30 ohms each and put them in series they would add to 1 H, Capacitance of 2.5 uf and a resistance of 60 ohms. So the inductance and resistance adds and the capacitance is half with two identical Inductors.

I don't have a 50 mh available to try but it would add capacitance and resistance so without knowing the actual numbers it's impossible for me to say for sure.
I think my theory above may work as it only adds to the resistance........once again I won't know until I try it out but will let you know tomorrow.

Regards,
George

[mac]

http://pisotones.com/Articulos/CrybabyMOD/CrybabyMOD.htm

see the pics at the end of the page.

mac

[John Lyons]

And in English as well. 

http://translate.google.com/translate?client=firefox-a&hl=en&ie=UTF8&oe=UTF8&twu=1&u=http://pisotones.com/Articulos/CrybabyMOD/CrybabyMOD.htm

[Joe Hart]

Could you take a small value inductor and run it in series with the existing one to "up" the inductance?
-Joe Hart

Hi Joe,

If you take two identical  500 mH inductors with a Capacitance of 5 uf each and 30 ohms each and put them in series they would add to 1 H, Capacitance of 2.5 uf and a resistance of 60 ohms. So the inductance and resistance adds and the capacitance is half with two identical Inductors.

I don't have a 50 mh available to try but it would add capacitance and resistance so without knowing the actual numbers it's impossible for me to say for sure.
I think my theory above may work as it only adds to the resistance........once again I won't know until I try it out but will let you know tomorrow.

Regards,
George

But could you add a cap or resistor in parallel to fine tune all of those parameters without changing everything too much?
-Joe Hart

[Paul Marossy]

Putting a resistor in series with the inductor just changes the DC resistance.

AFAIAC, that's like saying a certain guitar pickup sounds like this because it has X amount of DC resistance and ignoring everything else (which is more or less what the pickup manufacturers do as far as the public is concerned). Reality is that it is FAR more complex than that - there's inductance, a resonant frequency, DC resistance, eddy currents, some amount of capacitance, strength of magnets in gauss, magnet type, coil configuration, thickness of the wires, how many windings, metal cover or no metal cover, etc. Or like coming to conclusions about a guitar speaker strictly by measuring the DC resistance with no signal going thru it.

A wah inductor is not a guitar pickup, but there are some things in common. If anything, I would surmise that the "film can" inductor may not sound as good as the other types because it has a metal enclosure surrounding it.

I think an interesting test would be to see what the resonant frequency of all these different inductors is. I think that would be much more useful than measuring only the DC resistances and/or the exact value in mH. That would give you some idea of where the "sweet spot" is for each type. I could buy differences in similar inductors if they have differing resonant frequencies, that would shift around the "sweet spot" between each type. And it could account for differences people hear. I think that's missing from everyone's inductor testing, no one has ever measured the resonant frequency.