Wah Inductors. No hype. Just measurements.

[Stickman393]

So, just in case anybody wonders:

Fascinating stuff out there about inductors. All kinds of math equations that one can use to generally find the ballpark value of how many turns they need in order to do a thing.

It looks to me like, when we're talking about what tends to be used in wah pedals, the following tends to be true:

What is typically thought of as a "Halo" inductor is actually an 1811 (18mm diameter, 11mm tall) pot core inductor. This specific style can be bound together with a metal clip that gives the finished kit it's "halo" namesake.

The Stack of Dimes is typically a 1408 pot core, no clip, typically the halves are bound together by a screw through the center hole.

The RM-6 is a fine core to use, and toroids are quite common with dunlop's offerings.

For DIY purposes, I have no clue how one could feasibly do toroids. It's probably possible, but it would be extremely tedious.

RM-6, 1811P, and 1408P cores are sandwiched together with a "coil former" in between them.

The machine I'm building to make homebrew inductors will automatically wind an inductor when properly set up. I'd ultimately like to be able to make a bunch of these and, I dunno, like...dial in a good recipe. Throw em in some of the crybaby pedals I've accumulated through this little obsession along with a bunch of little mods and resell/try to make the money I've spent back.

The market's fairly saturated with folks that are doing this sort of thing anyways. I wanna do a few that are reasonably priced as a little passion project. To keep stickwife from getting too mad at me.

"Another wah pedal?!?"

 

[giovanni]

You could also use them in pedals like the Mystery Machine or the Conqueror fuzz. I wouldn’t mind trying some prototypes…

 

[Stickman393]

Promise, if I get some reasonably good prototypes, I'll be passing em out to long time members.

I picked up about 50 1811 pot cores recently that look like they'll be well suited to this purpose on paper. Cheap, too. Now all I need is to find appropriate coil formers and (maybe) clips/bases.

As side note: I get why the halos that are commercially available are priced up around 30 bucks plus a pop. A full set is about as much as smallbear's halo kit costs-maybe more.

my RMC wizard is made with a set of 1408 size pot core ferrites, or close to that spec. It looks like teese opted to make his own baseplates and waxed/glued the two halves together with the coil former in the center. This is likely to cut costs, as the clips and hardware don't really serve any purpose that can't be easily DIY'ed.

Also: interesting little tidbit. That early 80's Dunlop wah inductor is an 1811, just like the halos, but the steel screw in the center of it is actually contributing to the measured inductance. Or, was. That one broke due to my uncareful handling: no big loss. Measured out like a dog.

Which is probably why the later Dunlop inductors use brass: from what I've read, mixing magnetic materials in an inductor is generally frowned upon. Interesting.

 

[Stickman393]

Added another red fasel to the list.

So, something I've been musing about: why do these inductors measure differently at different frequencies? Why do some decrease, but then suddenly increase?

Well...I've come to a theory.

All these measurements interact with each other. No component is purely an inductor, or a resistor, or a capacitor. In fact, they are a combination of all three.

Two salient points, if I've got my EE theory correct here, which is absolutely *NOT* guaranteed:

1) Inductors contain parasitic capacitance.

• This parasitic capacitance cancels out some of the measured inductance.
  • The "parasitic" capacitance often *increases* with frequency.
  • The increase in parasitic capacitance acts against the inductance, as they are opposing forces.
  • Therefore, it is normal to expect that as frequency increases, measured inductance will decrease.

The way I'm thinking about this (and I have no idea if this is correct) is to consider two magnets (how do they work?). If I hold those two magnets close together, with one's north pole facing the other's south pole, the two magnets want to come together. This, I imagine, is illustrative of how a capacitor stores energy.

If I was to hold the north pole of one magnet up to the north pole of another magnet, the magnets fucking hate each other. Like kids with a high school beef. They are repelled: this, I imagine, is illustrative of how an inductor stores energy.

So, basically: with an increase in capacitance brought on by an increase in frequency, the inductor is less capable of repelling electrons along their path, as some attractive forces exist.

This would explain why some of these inductors read *lower* inductance at higher frequencies.

The second bit, here, has to do with reactance and impedance.

2) As frequency increases, reactance and impedance increases

• This acts to restrict the flow of AC current. It is measured in Ohms.
• We all know ohms law, yeah? What happens when you increase resistance, but voltage stays the same?
• Yup, current decreases. Gold star

So what does a decrease in current have to do with these measurements?

Well...this is something I'm still wrapping my noggin around, but it *may* have something to do with saturation.

An inductor's core material creates a magnetic field in proportion to the current fed through the inductor, but it will inherently be limited in terms of the size of the magnetic field it can ultimately create.

Saturation occurs when an inductor's core magnetic material is, basically, making as strong of a magnetic field as it can, and after that point it can no longer *really* do it's job. Waveforms traveling through the inductor begin to warp and distort. This is referred to as "non-linearity". This will show up as a *decrease* in measured inductance.

When current traveling through the inductor decreases past this point, the inductor begins to *desaturate*. This will show up as an *increase* in measured inductance.

Knowing these two things, I will make the following hypothesis:

As I increase the frequency fed through these inductors, I am both A) potentially increasing the amount of parasitic capacitance exhibited by each inductor (based on the design) and B) decreasing the current flowing through each inductor, which *could* desaturate the cores.

Point A would decrease measured inductance. Point B would increase measured inductance.

I believe that, perhaps, at low frequencies and around 100hz at 0.6v, that it is possible that the core of something like one of the Red fasels is saturated. As I increase the frequency, the current drops, parasitic capacitance increases, but it is not until I reach around 10KHz that the current drops low enough to de-saturate the core.

This shows up as parasitic capacitance causing the measured inductance value to decrease until the core is desaturated, at which point measured inductance appears to increase.

If that is correct, I could test out this theory in part by observing how waveforms fed through each of these inductors respond to differing frequency ranges on an oscilloscope. If the red fasel's waveform is distorted at lower frequencies but cleans up around 10khz, for instance, I'll know that inductor's core has desaturated at that point.

What this ultimately means is that the inductors that measure relatively stable inductance values across these audible/guitar-generated frequency ranges will tend to be *least* affected by parasitic capacitance and saturation. Meaning: the Sabbadius Soul and the whipple.

What does that mean for *toan*? Not the foggiest. I'm down a rabbit hole.

 

[Feral Feline]

Added another red fasel to the list.

So, something I've been musing about: why do these inductors measure differently at different frequencies? Why do some decrease, but then suddenly increase?

Well...I've come to a theory.

All these measurements interact with each other. No component is purely an inductor, or a resistor, or a capacitor. In fact, they are a combination of all three.

Two salient points, if I've got my EE theory correct here, which is absolutely *NOT* guaranteed:

1) Inductors contain parasitic capacitance.

• This parasitic capacitance cancels out some of the measured inductance.
  • The "parasitic" capacitance often *increases* with frequency.
  • The increase in parasitic capacitance acts against the inductance, as they are opposing forces.
  • Therefore, it is normal to expect that as frequency increases, measured inductance will decrease.

The way I'm thinking about this (and I have no idea if this is correct) is to consider two magnets (how do they work?). If I hold those two magnets close together, with one's north pole facing the other's south pole, the two magnets want to come together. This, I imagine, is illustrative of how a capacitor stores energy.

If I was to hold the north pole of one magnet up to the north pole of another magnet, the magnets fucking hate each other. Like kids with a high school beef. They are repelled: this, I imagine, is illustrative of how an inductor stores energy.

So, basically: with an increase in capacitance brought on by an increase in frequency, the inductor is less capable of repelling electrons along their path, as some attractive forces exist.

This would explain why some of these inductors read *lower* inductance at higher frequencies.

The second bit, here, has to do with reactance and impedance.

2) As frequency increases, reactance and impedance increases

• This acts to restrict the flow of AC current. It is measured in Ohms.
• We all know ohms law, yeah? What happens when you increase resistance, but voltage stays the same?
• Yup, current decreases. Gold star

So what does a decrease in current have to do with these measurements?

Well...this is something I'm still wrapping my noggin around, but it *may* have something to do with saturation.

An inductor's core material creates a magnetic field in proportion to the current fed through the inductor, but it will inherently be limited in terms of the size of the magnetic field it can ultimately create.

Saturation occurs when an inductor's core magnetic material is, basically, making as strong of a magnetic field as it can, and after that point it can no longer *really* do it's job. Waveforms traveling through the inductor begin to warp and distort. This is referred to as "non-linearity". This will show up as a *decrease* in measured inductance.

When current traveling through the inductor decreases past this point, the inductor begins to *desaturate*. This will show up as an *increase* in measured inductance.

Knowing these two things, I will make the following hypothesis:

As I increase the frequency fed through these inductors, I am both A) potentially increasing the amount of parasitic capacitance exhibited by each inductor (based on the design) and B) decreasing the current flowing through each inductor, which *could* desaturate the cores.

Point A would decrease measured inductance. Point B would increase measured inductance.

I believe that, perhaps, at low frequencies and around 100hz at 0.6v, that it is possible that the core of something like one of the Red fasels is saturated. As I increase the frequency, the current drops, parasitic capacitance increases, but it is not until I reach around 10KHz that the current drops low enough to de-saturate the core.

This shows up as parasitic capacitance causing the measured inductance value to decrease until the core is desaturated, at which point measured inductance appears to increase.

If that is correct, I could test out this theory in part by observing how waveforms fed through each of these inductors respond to differing frequency ranges on an oscilloscope. If the red fasel's waveform is distorted at lower frequencies but cleans up around 10khz, for instance, I'll know that inductor's core has desaturated at that point.

What this ultimately means is that the inductors that measure relatively stable inductance values across these audible/guitar-generated frequency ranges will tend to be *least* affected by parasitic capacitance and saturation. Meaning: the Sabbadius Soul and the whipple.

What does that mean for *toan*? Not the foggiest. I'm down a rabbit hole.

You mad scientist you.




Cool thread.



Midway through your quoted-here post, I started reading it in the voice of House of Frightenstein’s Professer Miller, lecturing away… Awesome, so well suited.

 

[Stickman393]

You mad scientist you.




Cool thread.



Midway through your quoted-here post, I started reading it in the voice of House of Frightenstein’s Professer Miller, lecturing away… Awesome, so well suited.

Honestly, not far off.

I'm maybe 30 years younger with a bunch more hair and a gnarly beard.

But the hair is just as crazy.

Probably *way* less educated too. I'm just an HVAC guy who should probably finish up his lunch and go back to work lest I receive any comments regarding why I didn't accomplish more today. Fuckin equivalent of a 2 year degree's what I've got.

Work work...

 

[Feral Feline]

Honestly, not far off.

I'm maybe 30 years younger with a bunch more hair and a gnarly beard.

But the hair is just as crazy.

Probably *way* less educated too. I'm just an HVAC guy who should probably finish up his lunch and go back to work lest I receive any comments regarding why I didn't accomplish more today. Fuckin equivalent of a 2 year degree's what I've got.

Work work...

Well, really, it’s about the VOICE…

Read this snippet from your post in Professor Miller’s voice:

When current traveling through the inductor decreases past this point, the inductor begins to *desaturate*. This will show up as an *increase* in measured inductance.

Knowing these two things, I will make the following hypothesis:

As I increase the frequency fed through these inductors, I am both A) potentially increasing the amount of parasitic capacitance exhibited by each inductor (based on the design) and B) decreasing the current flowing through each inductor, which *could* desaturate the cores.

Point A would decrease measured inductance. Point B would increase measured inductance.

Bottom line, to reiterate: cool thread.

 

[Stickman393]

Well, really, it’s about the VOICE…

Read this snippet from your post in Professor Miller’s voice:


A
Bottom line, to reiterate: cool thread.

Don't mind me. Just trying to duck any association with even the slightest facade of being a smart guy cause...uh....neurosies? We'll go with that.

 

[Feral Feline]

Don't mind me. Just trying to duck any association with even the slightest facade of being a smart guy cause...uh....neurosies? We'll go with that.

It’s not your fault.

 

[giovanni]

This is something people rarely talk about (except probably in high performance professional environments) but all components we design our circuits with are “ideal” components: capacitors, resistors and inductors are all modeled as perfect linear devices. This greatly simplifies circuit design (it’s hard enough to design for the non linearities of transistors!). However, real devices are definitely non linear. Even off the shelf capacitors and resistors present significant non linearities when outside of the frequency ranges they are designed for. And inductors are not exempt from such non linearities and as you can see, they seem to be affected by them even at relatively low frequencies (audio range). I wonder how much the non linearities actually contribute to the sound of certain Wahs?

 

[Stickman393]

And inductors are not exempt from such non linearities and as you can see, they seem to be affected by them even at relatively low frequencies (audio range). I wonder how much the non linearities actually contribute to the sound of certain Wahs?

This lais something I had considered as well. I need to go back and read RG Keen's article about one of the "magic" inductors he tested and how it generated odd harmonics when pushed...

What I do know is that certain factors make it easier for an inductor to become saturated: if it's built on an ungapped core, or if it's a toroid type, or if it uses an iron core.

What else: some of my early tests included transformers. It is absolutely possible for parasitic capacitance to overcome inductance. That is, at a high enough frequency, certain components with inductive qualities will lose those qualities and behave like a capacitor.

LEARNING IS FUN!

 

[GAStan]

Great thread! Thank you @Stickman393 !!!

You are absolutely correct about inductor having capacitance. You may be able to measure it with your LCR meter depending on how sensitive it is. This is something talked about on the Music Electronics Forum in the guitar pickups section. Be careful pickup winding can be a DEEP rabbit hole...kinda like pedal building LOL.

Forum - Music Electronics Forum

Forum Description

music-electronics-forum.com

 

[Stickman393]

Appreciate the heads up! I'll be winding pickups before too long here.

I imagine similar rules to wire in general apply to winding inductors...that is: thicker conductors=less resistance, greater capacitance, narrower vice versa.

As soon as I find my soldering iron with the tips made for inserting threaded inserts in 3d printed projects I'll be going to work making a few prototypes on a little CNC coil winder I'm building. Probably gonna use 3d printed coil formers to begin with here, using PETG.

I should have enough ferrite cores coming in today to make about 50...hopefully my research was correct and I'll be able to make something usable with a little trial and error.

Something that I'm considering now, as well, is how my hantek LCR meter is fixed at 0.6vac. I don't have the foggiest clue in how to determine exactly what kind of AC voltage a signal that runs through a wah pedal inductor would be. That, and with reactance being frequency-dependent, I imagine that in this use case that it could vary depending on the frequency range applied...

I can probably model that in spice to a certain extent. I'd like to know if 600mV is an unreasonably high value. It likely *would be* for the lower frequencies, when reactance is it's lowest, considering the 470k ohm resistor in series with the inductor.

I've read that there's a way to hack the meter I've got with a higher-end model's firmware that would open up the 0.3Vac test setting.

I'm, ah...probably not re-testing all these inductors though. Just sayin'.

 

[GAStan]

No problem, hope it helps.

I imagine similar rules to wire in general apply to winding inductors...that is: thicker conductors=less resistance, greater capacitance, narrower vice versa.

A coil is a coil, whether it's used on an inductor, on a pickup, a choke or any other number of things. And again you're correct, similar (if not the same) rules apply to the coil portion of each.
thicker conductors=less resistance, yes
I'd need to look into the conductor thickness vs capacitance portion so am not going to agree nor disagree.
In pickups the manner of the wind, that is nice even layers vs sloppy scatter wound  will affect capacitance and ultimately  can have an effect on tone. I cannot think of any reason this would not be true of any audio frequency inductor.

Disclaimer: much of this pickup specific information was learned from various forums such as this one but is tempered by a lifelong interest in electronics. Although I sat in my first Basic Electronics Course nearly 40 years ago I am by no means an authority so please take this information "with a grain of salt".

Pedals typically have 9vdc input. It wouldn't surprise me to see 600mV AC on the inductor. I don't have a wah pedal (yet) to measure or I would. Currently I'm gathering parts for a Tearjerker Wah...if I remember I'll take measurements when it's complete and post them here.

 

[Stickman393]

Honestly, with the fact that most of these inductors are under 50 ohms, and size of the loads in series with the inductor between 9Vdc and Ground, I'd be surprised if it got up to 0.6Vac. The bit about reactance, and how it's resistance will change depending on frequency, could make the difference there though.

Other news: well, I've added a few more inductors to the list. I went a little crazy on buying cheapies from different eras, and a couple that I got good deals on.

Added: two more ME-6's. A Budda Bud-Wah, another Thomas Organ TDK from 1976, Another brass screw pot core from the early 90's, An Eleca halo, A dunlop dreaded blue can of death (and not the cool, heavy metal kind) from 1986, and I'm in the process of adding a second Sabbadius Halo.

A few things have become extremely clear to me:

• the reactance graphs aren't particularly useful
• I need to consolidate some of the multiples into averages for the main chart
• There is a *great* amount of variance in the TDK inductors depending on the year
• The month I was born, Dunlop was making crybabies with shit inductors.

Also, I just picked up a couple of NOS Hotpotz 1's from Joe Gagan on ebay. Dude's cool AF. Just sayin.

 

[Stickman393]

I've updated the spreadsheet, we're up to 33 inductors as of right now. I've got...oh...five more crybabies incoming. They're all going to be between the 70's and early 90's era.

I've also separated the pages for measured inductance, Quality factor, and reactance. Helps make reading through a bit easier. The charts I've posted are increasingly difficult to read, but if you open the spreadsheet, you can hover over and individual item in the legend and it's line will be highlighted.

In terms of the history of the crybaby wah pedal, Joe Gagan has a part 1 regarding the he acquisition of Cry Baby by Dunlop from Thomas organ here.

 

[Stickman393]

First few tries of inductor winding:

Well, I've probably done about six at this point.

Things I've noticed:

The little machine I'm using isn't quite precise enough to really be able to wind well. I got it *pretty* close, though. It only really takes a dump on winding nice, even wraps around layer 4 or so. Then it scatter winds to hell.

That said, I've been able to nudge the process along with minor changes. Altering the reported thickness of the wire seems to help abit.

So far I'm at about 435 winds of #34 wire.

When I take the bobbin off and toss it in a ferrite core, I initially get about 475mH. Not bad!

Well, until I get up to about 4k. Then it falls off a cliff. The Q isn't scaling up like I've seen others do either.

My DC resistance is pretty low too. About 13.5 ohms. That's way below what other 18x11 pot cores I've seen have.

So...my thoughts are...A) gotta dial in the winds to make them more uniform, and B) gotta try a thinner wire, get that resistance measurement up around the 35-50 ohm range.

Pics of the mad science: