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DIY Stompboxes => Building your own stompbox => Topic started by: GBlekas on April 17, 2011, 07:47:19 PM

Title: Wah Inductors and magnetism
Post by: GBlekas on April 17, 2011, 07:47:19 PM
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

(http://i52.tinypic.com/1ztdgm.jpg)

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!  :icon_twisted:

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

(http://i53.tinypic.com/35anjg2.jpg)


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

(http://i56.tinypic.com/2zq5z55.jpg)

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

(http://i56.tinypic.com/sosrxg.jpg)

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

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

Title: Re: Wah Inductors and magnetism
Post by: Joe Hart on April 17, 2011, 08:10:29 PM
WOW! Have you tried a magnet on the inductor in the actual circuit? What was the change in sound?
-Joe Hart
Title: Re: Wah Inductors and magnetism
Post by: trjones1 on April 17, 2011, 09:01:50 PM
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.
Title: Re: Wah Inductors and magnetism
Post by: John Lyons on April 17, 2011, 09:20:43 PM
Cool stuff George. Go man go. Don't listen to that crack pot Gagan. ::)  :D :D :D
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 (http://www.diystompboxes.com/smfforum/index.php?topic=55476.0)

Title: Re: Wah Inductors and magnetism
Post by: trjones1 on April 17, 2011, 09:27:23 PM
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.
Title: Re: Wah Inductors and magnetism
Post by: defaced on April 17, 2011, 09:31:44 PM
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.  
Title: Re: Wah Inductors and magnetism
Post by: John Lyons on April 17, 2011, 09:41:20 PM
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.
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 17, 2011, 11:30:45 PM
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.
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 17, 2011, 11:49:49 PM
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?
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 17, 2011, 11:51:10 PM
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!   :)
Title: Re: Wah Inductors and magnetism
Post by: R.G. on April 18, 2011, 12:00:10 AM
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.

Quote
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.
Quote
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.

Quote
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.

Quote
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.

Quote
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.

Quote
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!  :icon_twisted:
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.

Quote
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.  :icon_lol:

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.
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 18, 2011, 10:36:43 AM
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.
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 18, 2011, 07:40:40 PM
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.

Quote
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.
Quote
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.

Quote
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.

Quote
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.

Quote
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.

Quote
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!  :icon_twisted:
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.

Quote
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.  :icon_lol:

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...

(http://i55.tinypic.com/am5gs0.jpg)

(http://i55.tinypic.com/214ectd.jpg)

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...
Title: Re: Wah Inductors and magnetism
Post by: Joe Hart on April 18, 2011, 09:53:38 PM
Could you take a small value inductor and run it in series with the existing one to "up" the inductance?
-Joe Hart
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 18, 2011, 10:08:53 PM
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.

(http://i55.tinypic.com/1zg97ad.jpg)

The introduction of the magnet affected the inductor's mH's and Capacitance but not the resistance.
(http://i54.tinypic.com/2sb0bd4.jpg)
(http://i55.tinypic.com/2ues5jn.jpg)
(http://i55.tinypic.com/2it0s5f.jpg)
(http://i53.tinypic.com/23qmp3.jpg)
Here is how repelling magnets affected the capacitance of the inductor.
(http://i55.tinypic.com/245zss9.jpg)

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

(http://i53.tinypic.com/2czvsjc.jpg)

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

Regards,
George
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 18, 2011, 10:18:47 PM
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
Title: Re: Wah Inductors and magnetism
Post by: mac on April 18, 2011, 10:26:48 PM
http://pisotones.com/Articulos/CrybabyMOD/CrybabyMOD.htm

see the pics at the end of the page.

mac
Title: Re: Wah Inductors and magnetism
Post by: John Lyons on April 19, 2011, 02:10:14 AM
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 (http://translate.google.com/translate?client=firefox-a&hl=en&ie=UTF8&oe=UTF8&twu=1&u=http://pisotones.com/Articulos/CrybabyMOD/CrybabyMOD.htm)
Title: Re: Wah Inductors and magnetism
Post by: Joe Hart on April 19, 2011, 12:40:55 PM
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
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 19, 2011, 01:14:34 PM
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.

Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 19, 2011, 01:28:54 PM
no one has ever measured the resonant frequency.




or, if they did, they didn't put their findings on the web ;)
Title: Re: Wah Inductors and magnetism
Post by: gmoon on April 19, 2011, 03:33:54 PM
First, I agree completely with Paul.

There's no magical, perfect inductor--musical taste is just too subjective, and the historical Vox/Thomas circuit IS adversely effected by various issues (impedance), and there are too many variables. What sounds great with one setup...well, you get it.

However, a resistor in series with the inductor doesn't exactly alter the DC resistance in the way speculated. I've done experiments with my "variable inductor" wah (as well as lspice sims). Raising the DC resistance of the inductor lessens the 'Q', increasing the bandwidth. It's the parallel resistance we're talking about--which is why a resistor in parallel with the inductor is generally considered the 'Q' adjustment for the circuit.

But a series resistor raises the "floor" of the other frequencies, so those rejected frequencies are louder. It's pretty obvious on the simulations, too. The two effects aren't that easy to differentiate sonically; they both "open up" the sound, just in different ways.

Personally, I think a really narrow bandwidth high 'Q' sounds BAD; not vocal at all.


@GBlekas
Have you read RG's "tech of wah pedals" page? 'Cause the info he references on testing the old Fasel inductor for a magnetic offset is there. It's a very interesting theory.

Inductors are the least "perfect" of any components. That's why they come in so many shapes, core materials, gaps, etc. It's tougher to turn theory into practice.

I'm 100% certain that a strong magnet will alter the inductance. But so does the magnetic permeability of the core material--the "slug" in a variable inductor isn't magnetic. So it's not really the inductance per se that matters when introducing that magnetic offset (because the offset is creating a "less perfect" inductor).

It's also gonna be really difficult to test the effects of a magnetic offset on inductors, due to the different constructions, geometry, strength of the perm magnet, distance (inverse square law stuff), etc. It's worth doing, but will be hard to quantify.

(I'm a little skeptical of the pisotones.com page. Flexible fridge magnets are really weak, and have a pattern of alternating-polarity stripes to boot. But I can't definitively say it's nonsense either, of course...)

It's cool to see all those inductors lined up, so pretty-like. I've got a old Thomas Organ wah, with the "Stack 'o Dimes." I gotta say that I hated that thing for years...but now I love it.  At least one article lists the "Stack" as the "holy grail" (although most cite the Fasel), so why did I hate it? Probably because my amplifiers were really sub-par back then (those external variables.)
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 19, 2011, 03:46:18 PM
However, a resistor in series with the inductor doesn't exactly alter the DC resistance in the way speculated. I've done experiments with my "variable inductor" wah (as well as lspice sims). Raising the DC resistance of the inductor lessens the 'Q', increasing the bandwidth. It's the parallel resistance we're talking about--which is why a resistor in parallel with the inductor is generally considered the 'Q' adjustment for the circuit.

But a series resistor raises the "floor" of the other frequencies, so those rejected frequencies are louder. It's pretty obvious on the simulations, too. The two effects aren't that easy to differentiate sonically; they both "open up" the sound, just in different ways.

Personally, I think a really narrow bandwidth high 'Q' sounds BAD; not vocal at all.

Yeah, I was being a bit simplistic, I know. Interesting results to the tests you have done, though. I think that is why they mention in the patent documentation that it was found necessary to add a resistor in parallel with the inductor, because the Q was so high that it didn't sound good.

To quote the patent:

"The innate Q of the circuit, in fact, is so high that it was found desirable to insert the resistor 36 (what we now commonly call the Q resistor) in order to admit some of the non-favored (off-peak) frequencies into the amplifier, so that they could pass to the output. Without the resistor 36, virtually the only frequency appearing at the base 24 (what we commonly call Q1) would be the only selected frequency, because of the high Q of the circuit. The presence of resistor 36 allows all frequencies to be developed to a certain extent thereacross, and hence passed to the amplifier."

So adding a resistor parallel with or in series with the inductor both have the same end result - they both lower the "Q".



Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 19, 2011, 06:07:51 PM
I posted the resonant frequency and bandwidth of the film can as well as a SOD and the text book ideal on page one of this thread.

What the number show was that the bandwidth of my particular film can was 1/2 of real world so adding the resistor should take care of that issue and bring it to where it needs to be. This is all being done by the numbers in attempt at getting at the root of why this wah doesn't sound right.

Also, if you were to take a great sounding real Clyde McCoy and reverse engineer each part actual value it takes the guess work and speculation out of things.

Also, playing guitar and wah for close to 40 years doesn't hurt.. ;)

In case you missed it here are today's numbers
(http://i53.tinypic.com/1085slc.jpg)

Any reason raising the bandwidth would be a bad thing?

I heard an issue with the inductor and the numbers show this film can to have half the bandwidth of other wah Inductors.
So, my train of thought is this very well could be the issue.
So, I soldered in a 22 ohm in series and have it in the wah now.
Testing next....
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 19, 2011, 06:21:02 PM
GBlekas :

I see that you have resonant frequency numbers on your simulation program or whatever that is from, but have you actually determined what the real resonant frequency is in the real world by testing them? That's the only way you're going to get reliable real world data. I don't know what those charts are from. Are you measuring them with a computer based program or something?

If you are basing all of your work on what a sim program is telling you, I think it can possibly lead you to false conclusions. I am interested to hear what the result is of your latest test, though.

EDIT: If those numbers are correct, then the resonant freq doesn't even seem to be a factor for a guitar in standard tuning. An open low E string is 82.41Hz...
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 19, 2011, 06:26:40 PM
The internet statement that the Fasel is/was the holy grail is bullshit!

That article, of course, is most likely why Dunlop reissued them.

Some of what you read is intentional disinformation put out for obvious reasons if you see who is putting it out there.

You have to wonder how the Fasel could be the holy grail when the most sought after wah is the Clyde McCoy and that has a Halo in it and not a Fasel.

Think about it.......

@gmoon  I read RG's stuff a bunch of years ago and probably where the magnet idea came from. I used two different strength magnets in my testing and the agree that the frig magnet is probably very subtle in what it would do.  Over all the magnet smooths the highs of the wah....or at least that is what my ears are telling me.

@Paul M  the Film can types for the most part sound great so I think you surmise incorrectly. It just happens that this particular one doesn't sound great.

The best thing I think that I have ever did to understand the wah was to take a Clyde apart.
What I found is not written on the web or if it is I haven't seen it.
The other thing was to do repairs for people.
I have found some things that people did to their wahs were actually excellent ideas and once again not written on the web because I think some of these ideas were done by accident.
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 19, 2011, 06:30:37 PM
GBlekas :

I see that you have resonant frequency numbers on your simulation program or whatever that is from, but have you actually determined what the real resonant frequency is in the real world by testing them? That's the only way you're going to get reliable real world data. I don't know what those charts are from. Are you measuring them with a computer based program or something?

If you are basing all of your work on what a sim program is telling you, I think it can possibly lead you to false conclusions. I am interested to hear what the result is of your latest test, though.

EDIT: If those numbers are correct, then the resonant freq doesn't even seem to be a factor for a guitar in standard tuning. An open low E string is 82.41Hz...

This is just readings of the inductor out of the wah circuit.
Since the issue I was having I know to be an inductor issue I isolated to figure out what was wrong.

Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 19, 2011, 06:38:03 PM
GBlekas :

I see that you have resonant frequency numbers on your simulation program or whatever that is from, but have you actually determined what the real resonant frequency is in the real world by testing them? That's the only way you're going to get reliable real world data. I don't know what those charts are from. Are you measuring them with a computer based program or something?

If you are basing all of your work on what a sim program is telling you, I think it can possibly lead you to false conclusions. I am interested to hear what the result is of your latest test, though.

EDIT: If those numbers are correct, then the resonant freq doesn't even seem to be a factor for a guitar in standard tuning. An open low E string is 82.41Hz...

This is just readings of the inductor out of the wah circuit.
Since the issue I was having I know to be an inductor issue I isolated to figure out what was wrong.

So then maybe it is all due to bandwidth. Or lack thereof. What program is that you are using? I've never seen it before.

@Paul M  the Film can types for the most part sound great so I think you surmise incorrectly. It just happens that this particular one doesn't sound great.

Yes, that is what I hear. I guess there's always at least one bad apple in the bunch, eh?  :icon_wink:
Title: Re: Wah Inductors and magnetism
Post by: merlinb on April 20, 2011, 05:04:49 AM
There is no way your inductors have a parasitic capacitance of over 4uF! You can't measure it just by hooking the inductor up to your cap meter.
Title: Re: Wah Inductors and magnetism
Post by: gmoon on April 20, 2011, 09:25:06 AM
So adding a resistor parallel with or in series with the inductor both have the same end result - they both lower the "Q".
That's reasonable. But not in quite the same way, so alterations wouldn't sound quite the same...


Adding a parallel or series resistor to an inductor will alter it's response...but it's not the same as changing the parallel or series resistance of the inductor itself...

The "bandwidth" values here-- we're all a little unsure how these values (and others) are calculated. But they should equate with 'Q', yes? That would be consistent--a higher 'Q', a narrower bandwidth, and a lower DC resistance all fit.

But like I said, personally, I don't like a wah with a really high 'Q'. A really narrow peak with 10 or 15dB of boost, surrounded by a floor with 20dB of rejection is...nasty harsh. But practically, it's better to have a lower DC resistance because it's easy to lower the 'Q' with a resistor or two than it is to raise it. Regardless of whether such adjustments sound identical with an inductor with inherent DC resistance...

Resonance is a factor of the "tuned circuit," not of the inductor by itself. I'm sure the resonant frequency (in an identical circuit) of all these inductors is reasonably close (given their inductance). I'm sure from an EE POV (I'm NOT an EE), that 10-20% variation in the inductance are as acceptable as similar variations in caps and resistors (and equally unavoidable).

But given all those other practical limitations of (cheap) inductors, then it's not the inductance per se that imparts the subtle differences... That's assuming there is a "holy grail" to be found  ;), and the good wahs aren't just "tuned in" well with the other components. (yeah, Halo, Stack or Fasel, doesn't matter to me.)

So if you're looking to uncover the subtleties; i.e. the non-linear response cited by RG, you'd be better off with a signal generator and a 'scope. And test it throughout the audio spectrum.  A meter (with an unknown test frequency) can't show you the harmonics, etc. I've got a similar meter, and I love it, but it's pretty limited.

Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 20, 2011, 10:42:39 AM
But like I said, personally, I don't like a wah with a really high 'Q'. A really narrow peak with 10 or 15dB of boost, surrounded by a floor with 20dB of rejection is...nasty harsh

Yeah, I HATE a wah that makes me cringe whenever I go to use it. I'd be modding that thing as soon as I got it, whatever it was, vintage or not.

But given all those other practical limitations of (cheap) inductors, then it's not the inductance per se that imparts the subtle differences... That's assuming there is a "holy grail" to be found  ;), and the good wahs aren't just "tuned in" well with the other components. (yeah, Halo, Stack or Fasel, doesn't matter to me.)

I don't really care about the actual inductor used, either. It's only one part of the bigger picture.

So if you're looking to uncover the subtleties; i.e. the non-linear response cited by RG, you'd be better off with a signal generator and a 'scope. And test it throughout the audio spectrum.  A meter (with an unknown test frequency) can't show you the harmonics, etc. I've got a similar meter, and I love it, but it's pretty limited.

I agree, there's got to be some better way of testing these inductors. I am still not convinced that it all just boils down to some certain DC resistance and mH value and then you get a magical inductor. There must be something else going on, harmonics or something.

I thought maybe I was onto something yesterday about resonant frequency, but if all types of indcutors average around 70Hz, it seems like a moot point. Anything above 70Hz will be diminished as it goes up in frequency, right? So if you had an inductor with that low of a resonant frequency, I would think that it wouldn't be a very lively sounding wah pedal, or would it? You wouldn't want the resonant peak too high because it would make it sound too harsh, but if it were too low, then it would be muddy and blah sounding. Then again, I keep coming back to you can't take the inductor out of context, because everything else in the circuit matters - because as you said, it's a tuned circuit.
Title: Re: Wah Inductors and magnetism
Post by: merlinb on April 20, 2011, 12:33:26 PM
I thought maybe I was onto something yesterday about resonant frequency, but if all types of indcutors average around 70Hz, it seems like a moot point. Anything above 70Hz will be diminished as it goes up in frequency, right? So if you had an inductor with that low of a resonant frequency, I would think that it wouldn't be a very lively sounding wah pedal, or would it?

There is no 70Hz resonance; GBlekas measure his inductor's wrongly. They don't have ~5uF of self capacitance!
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 20, 2011, 12:45:41 PM
I thought maybe I was onto something yesterday about resonant frequency, but if all types of indcutors average around 70Hz, it seems like a moot point. Anything above 70Hz will be diminished as it goes up in frequency, right? So if you had an inductor with that low of a resonant frequency, I would think that it wouldn't be a very lively sounding wah pedal, or would it?

There is no 70Hz resonance; GBlekas measure his inductor's wrongly. They don't have ~5uF of self capacitance!

Ha ha, good point!
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 20, 2011, 03:11:40 PM
There is no way your inductors have a parasitic capacitance of over 4uF! You can't measure it just by hooking the inductor up to your cap meter.

so, does this mean that the inductor does not have static capacitance? is it dependent on voltage applied?
Title: Re: Wah Inductors and magnetism
Post by: merlinb on April 20, 2011, 03:34:14 PM
so, does this mean that the inductor does not have static capacitance? is it dependent on voltage applied?
It will have some parasitic capacitance in parallel with it, but it will be in the order of picofarads. You would need a signal generator and o'scope (or audio millivoltmeter) to measure it.
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 20, 2011, 04:57:01 PM
thanks merlin. i was having trouble understanding what the calculator in george's post was looking for.

do george's findings still have some relevency ( not for freq range but general comparison) since his capacitance numbers are within a similar range?

gonna go play with the calculator to see if scaling the capacitance numbers down into pf ranges ( identical values for purpose of comparing) gives me any clues.
Title: Re: Wah Inductors and magnetism
Post by: merlinb on April 20, 2011, 05:15:06 PM
george's findings still have some relevency ( not for freq range but general comparison) since his capacitance numbers are within a similar range?
To be honest, I don't think so. For example, to get a self resonant frequency down below 10kHz where it *might* make some difference would require more then 500pF of self capacitance, and I don't think that's likely.
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 20, 2011, 05:33:20 PM
GBlekas :

I see that you have resonant frequency numbers on your simulation program or whatever that is from, but have you actually determined what the real resonant frequency is in the real world by testing them? That's the only way you're going to get reliable real world data. I don't know what those charts are from. Are you measuring them with a computer based program or something?

If you are basing all of your work on what a sim program is telling you, I think it can possibly lead you to false conclusions. I am interested to hear what the result is of your latest test, though.

EDIT: If those numbers are correct, then the resonant freq doesn't even seem to be a factor for a guitar in standard tuning. An open low E string is 82.41Hz...

This is just readings of the inductor out of the wah circuit.
Since the issue I was having I know to be an inductor issue I isolated to figure out what was wrong.

So then maybe it is all due to bandwidth. Or lack thereof. What program is that you are using? I've never seen it before.

@Paul M  the Film can types for the most part sound great so I think you surmise incorrectly. It just happens that this particular one doesn't sound great.

Yes, that is what I hear. I guess there's always at least one bad apple in the bunch, eh?  :icon_wink:

Yes sir! OK, ends up adding the 22 ohm resistor did it for this wah! Whoo hoo!
I will record it later and post a few sound clips of it.
Highs are where they should be and very sweet sounding, not harsh!

So, the band width theory totally nailed it for this inductor and wah.

The calculator tool was found here:
http://www.calctool.org/CALC/eng/electronics/RLC_circuit

 
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 20, 2011, 05:37:14 PM
There is no way your inductors have a parasitic capacitance of over 4uF! You can't measure it just by hooking the inductor up to your cap meter.

Well that's just great to know but if you could explain this to me it would be greatly appreciated.

I measured using the cap setting on this meter and went from inductor to inductor to inductor and then a 4.7 uf electrolytic cap.
Now, the 4.7 reads upwards of 5 so I think the meter is not all that accurate but it is reading capacitance.
I did not change meter settings and only changed item under test.

(http://i54.tinypic.com/t7l7y0.jpg)

Right now, barring the meter is reading the temperature in the room,   what I am thinking is that the 4.7 uf cap to ground in the wah circuit is no accident.
Title: Re: Wah Inductors and magnetism
Post by: phector2004 on April 20, 2011, 05:44:42 PM
You're measuring capacitance from both ends of a long conducting wire, not two separated sheets of conductor.

I think if you put a cap in series with it, you can get a better reading, as it will block DC, though you'll have to do further calculations.
Title: Re: Wah Inductors and magnetism
Post by: gmoon on April 20, 2011, 06:53:44 PM
GBlekas:

First, I'm glad you're happy w/your mod. It's not surprising that an inductor with a DC resistance of only 15 ohms would need something to lower the 'Q', and I'm glad you "discovered" this empirically (that's the best way to learn something).

I see from your photos that I have the exact same LCR meter (labeled BM-4070L, but I'm sure it's identical). That little minus sign? Means turn the unit dial down. I tried measuring a 550 mH inductor just now for capacitance, and also got -3.xx at the "20uF" setting. Keep turning that thing down, and it outputs some small value at each setting, all the way down to 75pF at the lowest setting ("2000pF"). So it's not the right tool for this metric...

That calculator? It's figuring responses in an LCR "tank circuit"--the R and the C aren't the DC resistance and parasitic capacitance of the inductor itself. They are external components. The calculator isn't exact enough to let you enter the variables for the inductor that deviate from an "ideal" inductor. In the calc, L, C and R are fixed, and therefore so is the resonant frequency.

So that's also why we couldn't understand how you found the "resonant frequency" for the inductors alone--that's dependent on the all the components (L and C, anyways) in the "tank," not just the inductor. A wah doesn't wah unless the resonant frequency changes, after all...
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 20, 2011, 07:21:35 PM
GBlekas:

First, I'm glad you're happy w/your mod. It's not surprising that an inductor with a DC resistance of only 15 ohms would need something to lower the 'Q', and I'm glad you "discovered" this empirically (that's the best way to learn something).

I see from your photos that I have the exact same LCR meter (labeled BM-4070L, but I'm sure it's identical). That little minus sign? Means turn the unit dial down. I tried measuring a 550 mH inductor just now for capacitance, and also got -3.xx at the "20uF" setting. Keep turning that thing down, and it outputs some small value at each setting, all the way down to 75pF at the lowest setting ("2000pF"). So it's not the right tool for this metric...

That calculator? It's figuring responses in an LCR "tank circuit"--the R and the C aren't the DC resistance and parasitic capacitance of the inductor itself. They are external components. The calculator isn't exact enough to let you enter the variables for the inductor that deviate from an "ideal" inductor. In the calc, L, C and R are fixed, and therefore so is the resonant frequency.

So that's also why we couldn't understand how you found the "resonant frequency" for the inductors alone--that's dependent on the all the components in the "tank," not just the inductor. A wah doesn't wah unless the resonant frequency changes, after all...

Interesting on a number of levels.
The wrong meter readings end up being very close to the value of the cap used in the classic wah circuit to ground.
Plugging this incorrect info into the calculations makes it appear that the issue with the inductor was headroom related and further calculations lead me to believe that simply adding a resistor should correct the issue. (keep in mind this pedal has been sitting on the shelf for a few years now because it didn't sound right)
So, I take all this incorrect data and try correcting the wah and for once the pedal actually sounds right...but none of this is right?
It worked like a charm but it's all wrong....that's rather funny!

I think the Q resistor was a 33k....so where would you go from 33k to increase headroom?


Title: RE: Wah Inductors and magnetism
Post by: gmoon on April 20, 2011, 08:01:07 PM
Actually, the irony here is that the results aren't wrong (even if the method was a little off.)

Plugging in a capacitance of 4 or 5uF gave your tank a resonant frequency in the audio range. A little low, but definitely in the ballpark. For better or worse, close enough to audio to not ring the WTF bell...

An LC tank works fine without any additional 'R'. You entered a small resistance value (the DC resistance for the inductors, which is fine). Increasing that resistance will reduce the 'Q' of your tank...which translates essentially into a wider band.

It's a subjective thing, but I've already said that too narrow a band (too high a 'Q') sounds nasty--to me anyway. Adding series (or parallel) resistance is one way to fight the icepick effect.

Despite the errors, you still recognized an outlier in the group--and a correlation between R and the bandwidth.

RE: 33K parallel R w/L -- that's going to be somewhat dependent on the DC resistance of the individual inductor... Your DC resistance measurements are pretty accurate, I think.  "Headroom"? I don't know. But higher R values will increase the 'Q' (narrow the band; limited by the actual DC resistance of the inductor) and lower will decrease the 'Q'.
Title: Re: RE: Wah Inductors and magnetism
Post by: gmoon on April 20, 2011, 08:03:34 PM
Ahhh hit quote by accident, and duplicated the response...
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 20, 2011, 08:06:50 PM
GBlekas:

Interesting that adding the 22 ohm resistor works for you. I'm curious about something, though. Have you ever checked out what is going on with Q1 in terms of voltage and maybe the Hfe in comparison to other good sounding "film can" wahs?

The reason I ask is because Q1 will only amplify what it sees coming back to the base from the inductor, and if the transistor gain is too low, then that might limit the "headroom" of those frequencies passing through besides the one selected by the operator. Just a thought based on what I've seen in my own wah pedal modding (you know, change the emitter resistor and it changes the sound some).

I'm just trying to think of reasons why an inductor that appears to be built to spec doesn't seem to sound right.
Title: Re: Wah Inductors and magnetism
Post by: GBlekas on April 20, 2011, 09:49:40 PM
GBlekas:

Interesting that adding the 22 ohm resistor works for you. I'm curious about something, though. Have you ever checked out what is going on with Q1 in terms of voltage and maybe the Hfe in comparison to other good sounding "film can" wahs?

The reason I ask is because Q1 will only amplify what it sees coming back to the base from the inductor, and if the transistor gain is too low, then that might limit the "headroom" of those frequencies passing through besides the one selected by the operator. Just a thought based on what I've seen in my own wah pedal modding (you know, change the emitter resistor and it changes the sound some).

I'm just trying to think of reasons why an inductor that appears to be built to spec doesn't seem to sound right.

From my tests Q1 & Q2 need to have the same HFE or there will be white noise at the output.
HFE's in this wah were both 250 but I think the sweetest sounding are in the 150 range with anything below being too weak.

At 1 minute Clapton shows his wah and I swear I can hear white noise suggesting mismatched transistors in that wah but I could be suffering from EJ syndrome.
The switch isn't too quiet either....
http://vimeo.com/8119784

Changing Re1 only works to a point. I like the way it fattens it up but not distortion so while I would never use a 510 ohm I would only go down to a 390 sometimes depending upon the tone of the wah.

Funny thing is the Clydes swept the upper end mostly and while not ice picky they were painful at home but worked great in the band mix.
Dunlops and mods I have heard often seem to sweep a much wider range of tones and while cool at home they aren't great in a band mix.

As far as the inductor goes I think it was just an unhappy accident that it ended up this way.
By far this was the worst film can I had ever heard up until I added that resistor to it.
This is the first time I had ever tried adding the resistor but typically I have found that any inductor below 30 ohms doesn't sound good to my ear.
Most inductors pulled from Dunlops and Vox wahs would read around 19 ohms so I have a box of those so perhaps I should try the series resistor with one of those to see how that works out.




Title: Re: RE: Wah Inductors and magnetism
Post by: GBlekas on April 20, 2011, 09:59:58 PM

 For better or worse, close enough to audio to not ring the WTF bell...


Never heard that saying before but it's really funny! ;D




Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 20, 2011, 10:15:43 PM
From my tests Q1 & Q2 need to have the same HFE or there will be white noise at the output.
HFE's in this wah were both 250 but I think the sweetest sounding are in the 150 range with anything below being too weak.

Interesting. I'm sure that the old wahs must be all over the map as far as the transistors go, depending on what wahs you want to talk about. The Italian ones seem to be the ones with the most variations in parts from what I have seen.  :icon_confused:

Changing Re1 only works to a point. I like the way it fattens it up but not distortion so while I would never use a 510 ohm I would only go down to a 390 sometimes depending upon the tone of the wah.

Yeah, just was pointing out that messing with the gain of Q1 does also changes things some.

As far as the inductor goes I think it was just an unhappy accident that it ended up this way.
By far this was the worst film can I had ever heard up until I added that resistor to it.
This is the first time I had ever tried adding the resistor but typically I have found that any inductor below 30 ohms doesn't sound good to my ear.
Most inductors pulled from Dunlops and Vox wahs would read around 19 ohms so I have a box of those so perhaps I should try the series resistor with one of those to see how that works out.

Huh, you might be able to use those things up after all.  :icon_wink:
Title: Re: RE: Wah Inductors and magnetism
Post by: gmoon on April 22, 2011, 11:18:20 AM
For better or worse, close enough to audio to not ring the WTF bell...
Never heard that saying before but it's really funny! ;D
Think it was just off the (cough) cuff...

Still-- it would be cool to see real data on the original premise--magnetic offset effect on wah inductors. Maybe RG, Merlin, PRR, (and I'm leaving other EEs out, for sure), etc., can give you some pointers about a test rig. For that matter, there's probably not much real data on those inductors at all, other than DC resistance and inductance.

Seeing as you've got an impressive vintage collection of those thingies...
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 22, 2011, 12:07:34 PM
in richard petersen's 1963 patent ( wow -wow trumpet sound for organ) that was used for the maestro boomerang, he included several drawings of ways to alter the frequency. one was an LDR being activated /modulated by a light bulb. another was metal or a magnet moving across the inductor actuated by a knee lever, since this was originally an organ design. cool stuff.
Title: Re: RE: Wah Inductors and magnetism
Post by: R.G. on April 22, 2011, 01:04:59 PM
Still-- it would be cool to see real data on the original premise--magnetic offset effect on wah inductors. Maybe RG, Merlin, PRR, (and I'm leaving other EEs out, for sure), etc., can give you some pointers about a test rig.
As far as I can tell, the magnetic offset data originated with me in the first half of the 1990s. At the time, you could have counted DIY effects makers on your fingers - well, maybe you'd need toes, but there were pretty few. I had a friend who ran a used-vintage-guitar shop and he knew that I was a mania...er, enthusiast  :icon_biggrin: about old pedals and would call me when he got something unusual in. He loaned me the original wah pedal I tested, along with the advice that if I messed it up, I bought it... gulp. It was reputed to be one with one of the "magic inductors" as well as they were known at the time.

Back then, I had access to a fully-equipped EE lab, and so I tiptoed in and set up some testing. I ran AC inductance, variation of inductance with frequency, self-resonance, Q at a variety of frequencies, all kinds of stuff and nothing showed up as markedly different from a (then) modern and decidedly un-magic wah inductor; at least nothing that wasn't explained by the usual measured R-L-C data.

For some reason I decided to run a spectrum analyzer on it. This was before PCs had sound cards capable of spectrum analysis, so I use a lab-grade HP setup feeding a high-purity sine wave to the inductor through a high resistance and measuring the spectrum of the voltage across it. What I found on the garden variety inductor was that for small signals, the resulting spectrum was a pure-ish sine that was not significantly different from measuring the sine generator itself until I pushed the signal level up to where the inductor started into saturation. Then I got distortion product spikes at 3x the input frequency, which is exactly what one would expect from a saturating inductor. It's clipping as the inductor can't support a voltage that high on its B-H curve.

When I tried the magic inductor in the same rig, all was the same until clipping started. What was distinctly different was that the first harmonic that came up was the **second** harmonic, not the third. Second harmonics cannot arise from symmetrical distortion products, they can only arise from asymmetrical distortion. I was so confused on this that I consulted one of my EE mentors about it. His response was "It sounds like there's an offset inside the inductor. That's what DC generators rely on to start up, remanent magnetic offset." A little more dinking turned up the verification. The inductor was going into saturation on one polarity of the signal first, and adding a little DC offset to the incoming signal could make this worse in one direction and better in the other.

The core itself was magnetized, and signal ran into saturation earlier on one polarity than the other. Looking at the circuit, I found that it puts a bit of DC current through the core for biasing Q1. The core material was fairly cheap and had some significant remanent flux, and there you are. The core was magnetized. Better ferrites don't have much remanence.

Those tests were almost 20 years ago. I posted the result to usenet (there was no web to browse or browsers to do it with at the time), and it appears that it's passed into myth and legend with the real info lost. It was a lucky accident that I had both a magic and non-magic inductor to measure and the equipment to do it. I don't know if soundcards could do the same test today. Maybe. Depends on the signal levels, I guess.

Quote
For that matter, there's probably not much real data on those inductors at all, other than DC resistance and inductance.
But it's not hard to get, given access to the inductors. I personally don't see much difficulty in getting a lot more info given the time and inclination to do it. I'd run inductance versus frequency versus signal level with AC signals, distortion spectrum on the results, probably self resonance and pulse-inductance tests on them, plus whatever else suggested itself.

There really isn't any magic there - only a technology you don't yet understand.
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 23, 2011, 11:58:39 AM
thanks for all the info, RG.

 you may recall, due to serendipity, we spent time at the mecca, your maniac/enthusiast friend's studio and home while we used to tour, he and D were very gracious to host us when were down there. his collection is strange and mindblowing. roland funny cat? sure, got one of those.  a dozen weird 60s italian made fuzzes? got that. drool worthy 50s cowboy guitars? check.
Title: Re: Wah Inductors and magnetism
Post by: R.G. on April 23, 2011, 02:18:00 PM
you may recall, due to serendipity, we spent time at the mecca, your maniac/enthusiast friend's studio and home while we used to tour, he and D were very gracious to host us when were down there. his collection is strange and mindblowing. roland funny cat? sure, got one of those.  a dozen weird 60s italian made fuzzes? got that. drool worthy 50s cowboy guitars? check.
It is a small world. Sad to say, he's recently moved to New Mexico, a town where a car passes through only a few times a day. Took his collection of esoterica with him. I'll miss him being here.
Title: Re: RE: Wah Inductors and magnetism
Post by: gmoon on April 24, 2011, 09:06:57 AM
Thanks for the info, RG. It fleshes out a bit what's in the geofex article. Makes me wonder if most of usenet isn't archived somewhere...

As far as I can tell, the magnetic offset data originated with me in the first half of the 1990s. At the time, you could have counted DIY effects makers on your fingers - well, maybe you'd need toes, but there were pretty few.
Compared to today, that's probably true. But it's gotta be a slight exaggeration--I built my first DIY projects in the late 70's, all thanks to Craig Anderton's wonderful book. And his column in Guitar Player ran for years, concurrent to the books he published. Plus the electronics rags always had a handful of guitar projects.

So there were more than a few builders out there. I wonder if there were fewer in the mid-90's, than the early 80's though...

@GBlekas:
What R.G. describes requires some substantial gear (and expertise) to tackle, eh?

You have any colleges or unis close by? There's gotta be an EE student with access to all this stuff who's also into guitar. Or a prof, for that matter... You might contact someone in the electrical engineering program.
Title: Re: RE: Wah Inductors and magnetism
Post by: GBlekas on April 24, 2011, 10:03:13 AM
Thanks for the info, RG. It fleshes out a bit what's in the geofex article. Makes me wonder if most of usenet isn't archived somewhere...

As far as I can tell, the magnetic offset data originated with me in the first half of the 1990s. At the time, you could have counted DIY effects makers on your fingers - well, maybe you'd need toes, but there were pretty few.
.

@GBlekas:
What R.G. describes requires some substantial gear (and expertise) to tackle, eh?

You have any colleges or unis close by? There's gotta be an EE student with access to all this stuff who's also into guitar. Or a prof, for that matter... You might contact someone in the electrical engineering program.


While I have been into electronics since 4 years old (believe it or not) R.G. Keen has been the internet guru for many, myself included,  and I am trying to digest what he has said. I am sure Joe Gagan and I aren't finished here.....but, we are persistent buggers and simply don't give up or go away that easily! :>)

That being said I am trying to figure out how to prove that offset using what ever necessary and maybe even learn something in the process.
I have a signal generator and Oscilloscope and looking into exactly how to set this all up to prove or disprove so any advice would be greatly appreciated.

I have ears so I know magnetism near the inductor smooths the highs so it's doing something without a doubt. I also like what it's doing as it sounds pleasant to the ears.

So, how would I set up a test rig?

R.G. said he saturated the Fasel inductor and it went into harmonic overtone quicker than a newer inductor but does this imply hooking up signal directly to the inductor or is the inductor in the wah circuit?  Is this set up so you can use the same wah circuit popping in different inductors to see how they behave under signal or is this signal hooked up directly to the inductor under test?

Just wanted to say thanks to you all for the input as it really is appreciated!

George

Title: Re: Wah Inductors and magnetism
Post by: gmoon on April 24, 2011, 10:22:55 AM
Excellent-- I was hoping you'd soldier (solder?) on...
Title: Re: RE: Wah Inductors and magnetism
Post by: R.G. on April 24, 2011, 10:58:05 AM
Compared to today, that's probably true. But it's gotta be a slight exaggeration--I built my first DIY projects in the late 70's, all thanks to Craig Anderton's wonderful book. And his column in Guitar Player ran for years, concurrent to the books he published. Plus the electronics rags always had a handful of guitar projects.

So there were more than a few builders out there. I wonder if there were fewer in the mid-90's, than the early 80's though...
Of course it's an obvious bit of hyperbole. There were definitely more than twenty. But the number of electronics tinkerers in general, and music tinkerers in specific were dramatically smaller than we have now, when there are over twenty *thousand* members at this one forum. The number of electronics experimenters went down dramatically in the 80s and 90s, as witness the magazines went out of publication. The 60 were probably the earlier peak, and the late 70s were a period of decline. I think that would match your perception. The internet reinvigorated the field with massively more available information and a new sense of community.

... I am sure Joe Gagan and I aren't finished here.....but, we are persistent buggers and simply don't give up or go away that easily! :>)
Good. It's a good place to do some detail work.

Quote
That being said I am trying to figure out how to prove that offset using what ever necessary and maybe even learn something in the process.
I have a signal generator and Oscilloscope and looking into exactly how to set this all up to prove or disprove so any advice would be greatly appreciated.

Proving it or not is easy. Find a magic inductor, one with reputed magic powers of tone, then take it all apart and use a hall effect magnetometer to measure the remanent field. The only reason I didn't do that was that I was promised a quick and messy death by the guy who loaned it to me if it didn't work right when he got it back.  :icon_biggrin:

Another measurement technique is to replicate the experiment. Feed a high purity sine from a high impedance source into the inductor and run a distortion/spectrum analysis on the result, which is what I did. I just glossed over the several hours of tinkering with various setups which showed nothing at all, but then I always did enjoy just being in labs.  :icon_biggrin:

Quote
I have ears so I know magnetism near the inductor smooths the highs so it's doing something without a doubt. I also like what it's doing as it sounds pleasant to the ears.
That fits with the asymmetrical magnetic offset theory. A touch of second harmonic has a sound reputed to be smoother and sweeter, and very hard to pick out by ear as even distorted at all.

Quote
So, how would I set up a test rig?
I suspect that a rig intended to feed a 100Hz sine as a current into the inductor and then measure the voltage with a sound card and program to run an FFT would do it. It's where I'd start.
Quote
R.G. said he saturated the Fasel inductor and it went into harmonic overtone quicker than a newer inductor but does this imply hooking up signal directly to the inductor or is the inductor in the wah circuit?

I isolated the inductor outside the wah. There are too many confusing variables inside the wah circuit. Besides, if the magic was actually in the inductor, it should be there with the inductor outside the wah circuit, too, right?

It could be argued that feeding the inductor from about  5V through a 470K resistor to fake the bias current going through it is necessary. I didn't do that one that way at the time (as I can remember - it's been nearly 20 years) but it's probably a good one to run for verisimilitude

The other thing I liked was feeding a small secondary winding in a non-magic inductor with a small current. This forces a magnetic offset on any core, and replicates sticking a magnet on the inductor, but has the disadvantage of acting like a transformer secondary. You need to feed this from a very high source impedance to keep it from loading down the main-inductor primary. I had mixed results with this back when. And since wah pedals are not my primary interest, I moved on.


Title: Re: RE: Wah Inductors and magnetism
Post by: Paul Marossy on April 24, 2011, 03:22:52 PM
When I tried the magic inductor in the same rig, all was the same until clipping started. What was distinctly different was that the first harmonic that came up was the **second** harmonic, not the third. Second harmonics cannot arise from symmetrical distortion products, they can only arise from asymmetrical distortion. I was so confused on this that I consulted one of my EE mentors about it. His response was "It sounds like there's an offset inside the inductor. That's what DC generators rely on to start up, remanent magnetic offset." A little more dinking turned up the verification. The inductor was going into saturation on one polarity of the signal first, and adding a little DC offset to the incoming signal could make this worse in one direction and better in the other.

Aha! I think THAT is the key element right there - the 2nd harmonic. IIRC, it was also a red Fasel inductor that was tested, not the "halo" inductor in the larger than life "holy grail" sell everything you have to get one Clyde McCoy wah pedal.

So then maybe it's possible that a few of the Clyde McCoy wahs have some inductors that have this DC offset happening in them as well. I am still not convinced that all you have to do is come up with the exact same inductance, DC resistance and make an exact physical reproduction to get a magical sounding inductor. Maybe those "magical" sounding wahs are actually wahs that have what should be considered faulty inductors, based on the information that RG provided above. And yet people find that desirable. Kind of like people prefer tubes over solid state devices. Tubes are imperfect devices with much higher THD than solid state devices, but I like the sound of them better.

Interesting stuff anyway.  :icon_wink:
Title: Re: Wah Inductors and magnetism
Post by: Philippe on April 24, 2011, 03:55:38 PM
Resistor selection being the key ingredient to good wah tone, isn't it amazing how inductor make/design/mojo/hyperbole has become the key distraction/element of all things pertaining to wah?

Title: Re: Wah Inductors and magnetism
Post by: R.G. on April 24, 2011, 07:05:49 PM
Resistor selection being the key ingredient to good wah tone,
It is? How exactly is that?
Title: Re: Wah Inductors and magnetism
Post by: Philippe on April 24, 2011, 11:40:51 PM
It is? How exactly is that?
Playing around with the Re1, Rq, & Rfb circuit resistors seems to make/have more noticeable impact than obsessing/scrutinizing the oftentime subtle differences between modern-day aftermarket Fasel red/yellow and/or Halo inductors.

It appears (to me) that as long as an inductor falls within a certain prescribed/recommended frequency/impedance range and isn't excessively microphonic, the aforementioned resistance modifications play a far larger role in determining the final sound of the wah circuit.
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 25, 2011, 10:55:36 AM
Playing around with the Re1, Rq, & Rfb circuit resistors seems to make/have more noticeable impact than obsessing/scrutinizing the oftentime subtle differences between modern-day aftermarket Fasel red/yellow and/or Halo inductors.

It appears (to me) that as long as an inductor falls within a certain prescribed/recommended frequency/impedance range and isn't excessively microphonic, the aforementioned resistance modifications play a far larger role in determining the final sound of the wah circuit.

I can agree with that based on my own personal experience.
Title: Re: RE: Wah Inductors and magnetism
Post by: MoltenVoltage on April 26, 2011, 02:04:58 AM
The core itself was magnetized, and signal ran into saturation earlier on one polarity than the other. Looking at the circuit, I found that it puts a bit of DC current through the core for biasing Q1. The core material was fairly cheap and had some significant remanent flux, and there you are. The core was magnetized. Better ferrites don't have much remanence.

Possibly ignorant question, but can years of use magnetize the core of the inductor and change its properties over time?
Title: Re: RE: Wah Inductors and magnetism
Post by: R.G. on April 26, 2011, 10:19:48 AM
The core itself was magnetized, and signal ran into saturation earlier on one polarity than the other. Looking at the circuit, I found that it puts a bit of DC current through the core for biasing Q1. The core material was fairly cheap and had some significant remanent flux, and there you are. The core was magnetized. Better ferrites don't have much remanence.

Possibly ignorant question, but can years of use magnetize the core of the inductor and change its properties over time?
That was my theory on how it got that way. There is a DC current through it in operation, the bias current for Q1. All by itself, that should cause some detectable magnetic offset; however I tested it out of circuit where the core material should have relaxed from the DC offset down to its remanant field value. What surprised me was that any remanence effect was detectable at all. I was used to working with power conversion style ferrites where remanence is a disaster to be avoided, and where air gaps were common.

For magnetically soft ferrites and electrical iron, the remanence (that is, the remaining static magnetic field when any external field is removed) is quite low. Permanent magnet material is selected for **high** remanence to keep a field. Transformer and inductor cores are selected for low remanence because they can saturate on the first cycle if started on the wrong phase, and because the core magnetizing losses get larger as the area inside the BH loop gets bigger, and high-remanence materials maximize the loop area. Taken together, those mean that an audio inductor should have nearly zero remanence, and any remaining field when the current is turned off should be very nearly zero.

Materials are not perfect,though. Remanence is a parameter of the material.

Air gaps in general reduce remanence by reducing the flux density to which the core is driven.

I do not know the exact material of the "magic" core I tested. It was unmarked, and I didn't have the equipment to do laser spectroscopy (that was in a lab I didn't have access to, and the staff there was carefully counselled to not let random engineers use the toys. No amount of promises of beer helped.  :icon_biggrin: )
However, cheapness and poorer properties went hand in hand and at the time, cheap high-mu ferrite had many imperfections. The best-fitting theory is that the ferrite was picked for highest permeability (mu) and other properties could go hang. That would minimize the amount of both ferrite and turns needed to get to half a henry.

The ferrite cores I had access to in the power lab were high quality, high mu, low remanence. I did do the necessary test, winding up a half henry inductor from new ferrite, then testing it. No second harmonic. I also had access to devices and power levels that would magnetize anything that could be magnetized. I did that to the new wind. No measurable second harmonic. I wound a second magnetizing winding on the newly-wound one and finally got second harmonic by driving the second winding with a constant current. The second winding I eventually abandoned as too complicated. The constant current source needed to not load down the Q of the inductor was as complicated as the rest of the wah circuit.

But people reported good results - or at least SOME results by sticking magnets to the core of a wah inductor, doing the same thing without a second winding.

Kewl.

Title: Re: RE: Wah Inductors and magnetism
Post by: Paul Marossy on April 26, 2011, 11:16:21 AM
However, cheapness and poorer properties went hand in hand and at the time, cheap high-mu ferrite had many imperfections. The best-fitting theory is that the ferrite was picked for highest permeability (mu) and other properties could go hang. That would minimize the amount of both ferrite and turns needed to get to half a henry.

Sound like a good theory to me. That's probably exactly what drove the inductor design - cost. Looking at some of the Italian made Vox wahs that had Fasels in them, cost looks like it was definitely the first consideration. Poor workmanship, really cheap wire, hodge podge of components, etc.
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 26, 2011, 11:36:41 AM
simple question. would it be possible to magnetically recreate this offset by winding a figure eight core with deliberately mismatched size or type of magnets for each half of the 8?
Title: Re: Wah Inductors and magnetism
Post by: RedHouse on April 26, 2011, 06:33:24 PM
I wonder if the cores are all the same dimensions?

In pickup winding with all else aside, altering the bobbin core shape effects the tone without effecting the meter readings.

5000 turns on a Strat bobbin doesn't sound the same on a humbucker bobbin, even if you move put the alnico magnets into the humbucker bobbin.

Just a thought, ok now, back to your regularly scheduled thread.
Title: Re: Wah Inductors and magnetism
Post by: R.G. on April 26, 2011, 07:27:12 PM
simple question. would it be possible to magnetically recreate this offset by winding a figure eight core with deliberately mismatched size or type of magnets for each half of the 8?
Maybe...  :icon_biggrin:

I wonder if the cores are all the same dimensions?
Nope. All of the follow on cores were seemingly obtained by asking a vendor of wound ferrite cores to give them half a henry, with a Q greater than X at frequency Y and DC resistance below Z. I'd wager a significant amount of money that the specs for the companies making wahs didn't include ferrite type, BH-curve remanence, or even loss curves. IMHO, the offset effect was the purest kind of happy accident.
Title: Re: Wah Inductors and magnetism
Post by: mac on April 26, 2011, 08:00:55 PM
Joe,
I was thinking a few days ago about making the core not a cylinder but like this

(http://www.worldbarsupply.com/images/3QAluminum-Ice-Bucket.jpg)

If an external magnet altering the shape of the magnetic field has some effect in tone, why not trying a not symetrical core shape? Just for fun.

mac
Title: Re: Wah Inductors and magnetism
Post by: Joe Hart on April 26, 2011, 09:05:42 PM
I tried a magnet on the inductor of my Vox 845 and it seems to add a bit of "growl" to the midrange and to smooth the transition out a tiny bit. I'd say all-in-all it's pretty subtle, but the changes do seem to be there. Very interesting. I will say that my 845 is the best wah I've ever played stock (I like my modded 847 a little better). Too bad it has a lot of SMD components and a lot of extra components that I can't figure out. I'd love to fine tune it (and make it the best wah I've ever played??), but I can't figure out what all the parts are. Oh well. But anyway, that's my take on the magnet thing. It is a very interesting mod (and super easy to do)!
-Joe Hart
Title: Re: Wah Inductors and magnetism
Post by: george on April 28, 2011, 02:18:49 AM
Playing around with the Re1, Rq, & Rfb circuit resistors seems to make/have more noticeable impact than obsessing/scrutinizing the oftentime subtle differences between modern-day aftermarket Fasel red/yellow and/or Halo inductors.

It appears (to me) that as long as an inductor falls within a certain prescribed/recommended frequency/impedance range and isn't excessively microphonic, the aforementioned resistance modifications play a far larger role in determining the final sound of the wah circuit.

I can agree with that based on my own personal experience.

My personal experience not being as extensive as Paul's or Phillipe's, but I would have to disagree .... ::)

I have a GCB-95 wah that I first tried all the mods on, then put a yellow fasel in, still didn't like the sound of it.  Then I put in a red fasel which I liked, but found the mods made it too bassy so I took them out and I now like the wah fine with just the stock resistor values!  So in my experience the difference definitely isn't subtle.   So much so I have a yellow fasel which I just don't need anymore.

Sure the differences may be in resonant frequency and/or impedance but I just haven't been very scientific I suppose.
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 28, 2011, 08:50:32 AM
i never found a modern fasel red or yellow that i thought sounded worth a crap. i grind them up and eat them for breakfast.
Title: Re: Wah Inductors and magnetism
Post by: gmoon on April 28, 2011, 11:28:22 AM
@george
No one's denying that swapping inductors can change the sound.

What Paul and Phillipe are saying is that the inherent DC resistance alone has a large effect on the Q (bandwidth)-- and unlike the inductance variation, that can be compensated for.

GBlekas chart on page one shows the DC resistance of his collection varies between 14.4 and 106.3 ohms. Sure, there's quite a variation in inductance, too. But we CAN tune the circuit for that difference in resistance (actually, we can tune it for the inductance variation, too).

I've done quite a bit of hacking w/variable inductors in fairly different circuits, as well as running simulations. The Q factor in ALL instances decreases as the DC resistance of the inductor increases. However, it decreases MUCH more prominently at higher frequencies. I.E., an inductor with higher resistance will tend to have "mellower" highs, while being a more effective filter in the lower frequencies. How much the Q decreases (and where) depends on the other components in the circuit (as well as the inductor itself).

Of course, tuning the Q via external resistors isn't quite the same as the inherent DC resistance of the inductor itself. It's just arguable that most of the "magic inductor" effect could be due to various other variables.


RE: 2nd order harmonic

RG and the EEs can slap me down hard on this, but it seems to me that any LCR variable filter is a harmonic-generating machine, including even-order--when you sweep the filter.

A LCR resonant filter, or any thing with hysteresis, has a time component by nature. If there's an inductor (w/reluctance and permeability) there's a time-dependent rebound. So when the filter sweeps, there's a mixture of signals that's probably asymmetrical (with some resultant even-order harmonics--probably).

I hate to resort to the "but I can hear it" argument, but in my variable inductor experiments it's pretty obvious that altering the inductance rapidly has a greater effect than a slow change. I think that's why a resonant wah filter is so much more successful than other alternatives like the Twin-T, etc.

But  that's somewhat different than RG's magnetic offset, which in theory would be generating 2nd order harmonics without the sweep.

Personally, I've heard (and built) enough tube amps to take the whole "Class A" and "even-order distortion magic" thing with a grain of salt. There have certainly been a lot of BAD tube amps out there. An amp with only a 2nd order harmonic is pretty boring. Most amp mods strive to get more odd-order harmonics...

I'm not discounting this completely, but it's right back to "personal preference" again.
Title: Re: Wah Inductors and magnetism
Post by: Paul Marossy on April 28, 2011, 12:05:08 PM
I've done quite a bit of hacking w/variable inductors in fairly different circuits, as well as running simulations. The Q factor in ALL instances decreases as the DC resistance of the inductor increases. However, it decreases MUCH more prominently at higher frequencies. I.E., an inductor with higher resistance will tend to have "mellower" highs, while being a more effective filter in the lower frequencies. How much the Q decreases (and where) depends on the other components in the circuit (as well as the inductor itself).

That's an interesting bit of info there. That could explain a few things, depending on what type of changes you are expecting to hear when you change out an inductor. Any differences I *think* I have heard solely by replacing the inductor were very very subtle. So much so that I had to question if I really heard anything at all.
Title: Re: Wah Inductors and magnetism
Post by: Philippe on April 28, 2011, 12:41:15 PM
i never found a modern fasel red or yellow that i thought sounded worth a crap. i grind them up and eat them for breakfast.
Being mass-produced as a retro-inspired component, some/many probably deviate a bit from the 'ideal numbers' as the inconsistancies & variances of modern-day Fasels have been well documented/noted by various builders.

Prefer a spec'd halo myself...along with the 'dialed-in' resistance values.
Title: Re: Wah Inductors and magnetism
Post by: RedHouse on April 28, 2011, 12:47:14 PM
I'm with George on this one.

I too have tried many inductors over the years, I settled on the RED fasel which does it for me.
(that and replacing the MPS-A18 transistors)
Title: Re: Wah Inductors and magnetism
Post by: joegagan on April 28, 2011, 12:55:46 PM
great points all around. thanks to everyone for their input.

phillipe, i base my statement on modern fasels after eartesting ( tuning each as tested) - i have run these tests on 4 yellows and three reds, they all exhibit the same limp-weiner sound to me. if you want a sweet sounding (  think sonic rainbow ) wah but that is also very boring, use a modern fasel. just my opinion.

that said, what i am looking for in a wah is a resonant circuit that is lively, with a growl-ey bark in the low mids to mids. this is what makes wahs dynamic and fun to me. if a wah just has a nice filtering sweep from high to low, it might as well be a twin T circ. to me, the advantage of the inductor is the ability to create a very dynamic instrument from it.

i have seen 10 years of people giving opinions on which inductor they like best, but i would guess that the majority of them simply swapped inductors ( maybe did the usual 33k mod, Q1 emitter R mod etc) but they did not take the time to tune each inductor with its ideal cap to ground. it is near impossible to say which inductor sounds best without taking the time to tune each one individually. and this makes AB comparing nearly impossible.
Title: Re: Wah Inductors and magnetism
Post by: Philippe on April 28, 2011, 04:01:10 PM
that said, what i am looking for in a wah is a resonant circuit that is lively, with a growl-ey bark in the low mids to mids. this is what makes wahs dynamic and fun to me. if a wah just has a nice filtering sweep from high to low, it might as well be a twin T circ. to me...
Can't argue with that assessment.

A great wah tone is reminscent of barreling down an open road (or highway) with the sound of dual Weber sidedraft carburators running wide open...that throaty growl is unmistakeable.

Sounds like you'd dig the sound of a Macari wah with the scooped mids as recorded/heard on Disraeli Gears/Wheels of Fire.
Title: Re: Wah Inductors and magnetism
Post by: gmoon on April 29, 2011, 10:07:34 AM
I've done quite a bit of hacking w/variable inductors in fairly different circuits, as well as running simulations. The Q factor in ALL instances decreases as the DC resistance of the inductor increases. However, it decreases MUCH more prominently at higher frequencies. I.E., an inductor with higher resistance will tend to have "mellower" highs, while being a more effective filter in the lower frequencies. How much the Q decreases (and where) depends on the other components in the circuit (as well as the inductor itself).

That's an interesting bit of info there. That could explain a few things, depending on what type of changes you are expecting to hear when you change out an inductor. Any differences I *think* I have heard solely by replacing the inductor were very very subtle. So much so that I had to question if I really heard anything at all.


It's a pain to pull a web-friendly graphic from LTspice, but here's a couple pics to illustrate, at two different inductance values. The inductance values and circuit are the same in each plot, only the series resistance changes--15 ohms (green) vs 105 ohms (red). That hifreq peak is under 4dB for the higher resistance value, vs about 18 dB for the lower resistance inductor.

low freq response
(https://lh5.googleusercontent.com/_Z7b6PJeTtfE/Tbq8YGu6B8I/AAAAAAAAAkI/eLmdALI_CBY/s800/lowfreq.jpg)

high freq response
(https://lh3.googleusercontent.com/_Z7b6PJeTtfE/Tbq8XkFSYvI/AAAAAAAAAkE/8_nT3gG1XJM/s800/highfreq.jpg)


Yes, this isn't the classic Vox/Thomas/McCoy circuit. But I've simulated and tested a ton of different LCR tank circuits, (following boost, NFB, w/opamps, jfets, bjts) and they all have the tendency to drop off more in the higher frequencies when the DC resistance is higher.  How precipitous it drops depends on a lot of factors, but this just illustrates how isolating and changing one factor alone (not the inductance) can have a pretty large effect.

The change is still there, but somewhat less prominent in the Vox circuit because a 500 mH inductor is on the edge of the sweet spot for a linear response in the audio spectrum. A higher value inductor (1-2 H) would probably be even better, but bigger and more expensive.

I know there's tons of other variables, too--ferrite material, geometry, etc.

Fun stuff!
Title: Re: Wah Inductors and magnetism
Post by: RedHouse on April 29, 2011, 11:21:49 AM
... the sound of dual Weber sidedraft carburators running wide open...that throaty growl is unmistakeable...

Back in the 80's I had a Datsun (Nissan) 260Z with that inline-6 and it had 2 of those Weber dual side draft carbs, I had the hood off for a while and you are so totally right, the sound they make is un-mistakable.

All was well and good until I swapped out the L6 for a 283 Chevy motor, bad move that. 
Title: Re: Wah Inductors and magnetism
Post by: aquaboy1993 on April 29, 2011, 01:40:08 PM
Just to add in a thought here from a guy who has never modded a wah before....  I do have one ready to attack however.

Talking about the magnetism of an inductor.  The little Rat Shack transformers have both primaries and secondaries.  Typically you cut the primaries and only use the secondaries as an inductor.  But is is possible/useful to pass some DC current through the primary?  Wouldn't that create a magnetic state in the core that would then be passed onto the secondaries?

Or am I just thinking out of the bottom of my chair?   ???

Mark
Title: Re: Wah Inductors and magnetism
Post by: RedHouse on April 29, 2011, 02:02:56 PM
...is possible/useful to pass some DC current through the primary...

That's been talked about here before over the years, nobody really pursued it though. Boldly go dude!
Title: Re: Wah Inductors and magnetism
Post by: Philippe on April 29, 2011, 02:23:05 PM
All was well and good until I swapped out the L6 for a 283 Chevy motor, bad move that. 
That short-block Chevy 283 is a terrific motor...a popular engine conversion on Jaguars, Toyota Landcruisers & Datsun Zs during the late 70s-early 80s.

I'd  imagine that a V8 sort of changed the overall personality of your Zcar.
Title: Re: Wah Inductors and magnetism
Post by: ORK on April 29, 2011, 04:17:47 PM
Just to add in a thought here from a guy who has never modded a wah before....  I do have one ready to attack however.

Talking about the magnetism of an inductor.  The little Rat Shack transformers have both primaries and secondaries.  Typically you cut the primaries and only use the secondaries as an inductor.  But is is possible/useful to pass some DC current through the primary?  Wouldn't that create a magnetic state in the core that would then be passed onto the secondaries?

Or am I just thinking out of the bottom of my chair?   ???

Mark

Or just short the primary?
Title: Re: Wah Inductors and magnetism
Post by: R.G. on April 30, 2011, 12:25:35 PM
Just to add in a thought here from a guy who has never modded a wah before....  I do have one ready to attack however.

Talking about the magnetism of an inductor.  The little Rat Shack transformers have both primaries and secondaries.  Typically you cut the primaries and only use the secondaries as an inductor.  But is is possible/useful to pass some DC current through the primary?  Wouldn't that create a magnetic state in the core that would then be passed onto the secondaries?
That was one of my first efforts. I tried it, didn't notice it being any better. But transformer iron has a saturation flux density about 5X the saturation density of ferrite, and a different transition into saturation, so it may be that iron cores are not well suite to this line of attack, or need a lot more TLC to get right, whatever "right" is.

Or just short the primary?
You have to drive the secondary with a high impedance current source to avoid doing exactly that. And high impedance current sources are noisy, so it adds extra hiss for you, too. The added magnet biases the core without adding hiss.
Title: Re: Wah Inductors and magnetism
Post by: nepalnt21 on November 29, 2018, 03:54:52 PM
i didn't really want to start a new topic, as this thread seems like a pretty decent start to an ultimate wah inductor + magnetism compendium. i just wanted to share my experience with this subject, as it pertains to a breadboarded wah circuit (i pretty much stuck with r.g. keen's tech of wah circuit, switched the input resistor and cap order, for no good reason).

i have three inductors out-of-circuit to play with: a newfangled dunlop yellow "fasel", a plain black cylinder inductor from a standard cgb-95, and a "halo" style from small-bear (eleca is the brand).

i gathered up magnets from various sources, from really weak 16th inch by quarter inch ceramic discs that can barely hold their own weight to a couple one-inch diameter neodymium discs.

the one i settled on is probably a half-inch in diameter, maybe at most 8th inch thick, probably rare-earth magnet from a broken drive motor for a conveyor system node.

here is what i noticed: i really have to play with it to find a sweet spot. if i just willy-nilly stick it, chances are, the inductor will turn into a useless short and the wah pedal will not wah, or it will change nothing about the inductor, and will sound just like it did before it was placed.

not only do i move it around the whole surface of the inductor to find a sweet spot, but i also change the orientation of the magnet.

i have the yellow fasel on the breadboard at the moment (makes the most drastic differences), with the magnet on its spine (not sure if positive or negative), in the middle of the white plastic plate of the inductor.

i changed out a few values (im guessing that if the magnet lowers the inductance, lower inductances mean a more trebly sweep), put in a bigger sweep cap, and i like a lower value on the "q" resistor (parallel to the inductor) as people call it. everything else seems to be stock, i think i messed with the 22k (at the 9v+ to collector of q1 position) value, lowered it i think (all of the resistors are wired as rheostats atm, one leg out of circuit), and the 1k5 "midrange" resistor i tuned till i liked the midrange, havent measured yet.

some positions of the magnet make EXTREME changes to the sweep. before the point where the magnet is making too strong of an effect (i think it pushes the sweep out of audible range, personally) the sweep is VERY trebly. it is completely unusable except for the higher harmonics. sounds more like a chipmunk going "wee wee wee", instead of a wah pedal wah-ing. i tend to like the "ee" sound at the toe part of the range, so i play with it JUST until the point where it shows, and fiddle with the rest until the midrange and bass are balanced with it.

dang, i really want all the sounds, actually. lower sweeps (stacking two series inductors, or raising the value of the sweep cap) are great for muted "waka waka" things, and filtering crunchy tones.

anyway, the halo style inductor sounds better stock than with the magnet, which makes very little difference, even in the position where it DOES finally make a difference. maybe it is the metal brackets, which also make it a pain to work with the magnets.

i really want to make a video to demonstrate these experiments.

hope this thread necromancy will be tolerated!
Title: Re: Wah Inductors and magnetism
Post by: Rob Strand on November 29, 2018, 04:26:23 PM
You have to watchout with those magnets.   Some ferrites can be permanently changed if you put a strong magnet like a rare-earth magnet on them.

The other issue is if you put a magnet on an inductor and take it away it can magnetize the ferrite so even though there's no magnet it is not longer the inductor it was before.  You will need to demagnetize the ferrite using an AC coil, then slowly move the coil out of the field.

Quote
some positions of the magnet make EXTREME changes to the sweep. before the point where the magnet is making too strong of an effect (i think it pushes the sweep out of audible range, personally) the sweep is VERY trebly. it is completely unusable except for the higher harmonics. sounds more like a chipmunk going "wee wee wee", instead of a wah pedal wah-ing.

Yes, the magnet makes the inductance smaller.    If you are DIY'ing an inductor you can add taps to the coil.   For each tap you can try tweaking the cap, series resistance and Q resistor.
Title: Re: Wah Inductors and magnetism
Post by: nepalnt21 on November 29, 2018, 04:52:17 PM
that's good to know, thanks. luckily i am not particularly attached to any of these three inductors. lotsa fun!

btw, in what way/ why can the ferrite be damaged?
Title: Re: Wah Inductors and magnetism
Post by: Rob Strand on November 29, 2018, 05:22:38 PM
Quote
why can the ferrite be damaged?
I've never seen the details explained but I remember some manufactures mentioning exposing some of their ferrites to strong fields would cause irreversible change. I guessed it can somehow screws-up the structure of the ferrite at the magnetic domain level.  From that I suspect other ferrites are probably affected but in a minor way.   Those rare-earth magnets are pretty darn strong they will push most materials well into magnetic saturation.

Unless you have a demagnetizer it's hard to completely remove the magnetization from something.   In the past I first use the magnet I magetized something with in reverse then use a demagnetizer.   Another way is to drive a gradually decreasing AC current into the coils of the device (/inductor) but you need to start with a lot of current and you have to be careful not to fry the coils due to over current!
Title: Re: Wah Inductors and magnetism
Post by: nepalnt21 on November 29, 2018, 09:29:40 PM
in case anyone cares:



sorry if the guitar sounds like poo, i was focused on wah sounds rather than making sure my strings were in-tune.

after the video, i tried two inductors in series, with one taking the magnet. sounds nice once i got the sweep cap dialed in.

i swear i had it sounding like a univibe last night... there was a clear volume drop at the heel-down position, so it made this AMAZING swell with a nice subtle wah. i wish i could find that arrangement again, let alone make it repeatable once in an enclosure...
Title: Re: Wah Inductors and magnetism
Post by: Rob Strand on November 29, 2018, 09:58:37 PM
Quote
in case anyone cares:
It actually won't play on my PC I'll have to pull-out my unix box.