Opinions about Wah Inductors?

[tubelectron]

23,

The inductor you see is a "scratch part chosen by trial and errors" (and measurement of course !) : it is a small audio transformer coming from an old '50s-'60s tube military transmitter-receiver spare part supply kit. The part is from the brand WALTHAM-RAYTHEON, ref. N° TF1A10. I use the primary only, which makes an 1,259 H / 85,2 ohms DC.

My purpose was to tell that - again - you can have good surprises with oddity coils as wah inductors. But of course, you may need to determine the rest of the circuit according to the result you want. This one, for instance, gives me a very vocal wah, but nonetheless having a wide and progressive range.

A+!

[23]

Love it............

[Paul Marossy]

23,

The inductor you see is a "scratch part chosen by trial and errors" (and measurement of course !) : it is a small audio transformer coming from an old '50s-'60s tube military transmitter-receiver spare part supply kit. The part is from the brand WALTHAM-RAYTHEON, ref. N° TF1A10. I use the primary only, which makes an 1,259 H / 85,2 ohms DC.

My purpose was to tell that - again - you can have good surprises with oddity coils as wah inductors. But of course, you may need to determine the rest of the circuit according to the result you want. This one, for instance, gives me a very vocal wah, but nonetheless having a wide and progressive range.

But wait a minute... the majority of people seem to think that the inductor has to be EXACTLY 500mH with EXACTLY a certain DC resistance and made a certain way for it to sound good and right. Let me clean my ears, did I just hear what I think I did? You used a 1.3H inductor and it sounds good? That just proves my point that the inductor is not everything when it comes to the wah circuit.  

I've never tried a 1H inductor in any of my wahs, I should just for kicks. I have a couple lying around wanting to be used for something...

[tubelectron]

23,

The inductor you see is a "scratch part chosen by trial and errors" (and measurement of course !) : it is a small audio transformer coming from an old '50s-'60s tube military transmitter-receiver spare part supply kit. The part is from the brand WALTHAM-RAYTHEON, ref. N° TF1A10. I use the primary only, which makes an 1,259 H / 85,2 ohms DC.

My purpose was to tell that - again - you can have good surprises with oddity coils as wah inductors. But of course, you may need to determine the rest of the circuit according to the result you want. This one, for instance, gives me a very vocal wah, but nonetheless having a wide and progressive range.

But wait a minute... the majority of people seem to think that the inductor has to be EXACTLY 500mH with EXACTLY a certain DC resistance and made a certain way for it to sound good and right. Let me clean my ears, did I just hear what I think I did? You used a 1.3H inductor and it sounds good? That just proves my point that the inductor is not everything when it comes to the wah circuit.  

I've never tried a 1H inductor in any of my wahs, I should just for kicks. I have a couple lying around wanting to be used for something...

Hi Paul,

Yes, this inductor sounds good despite the fact that it is way different from the usual specs. But there's no magic about "inductors from scratch" : some of them will work, some don't. I didn't measured the Q factor of this one, in order to compare it to "official" inductors : it probably have an undisclosed importance...

Another very important point about "scratch inductors : microphonic insulation. I barely mount these inductors directly on the PCB or on the chassis, I prefer put them in a foam sandwich (see my pictures in my previous post), but I have been nonetheless often forced to discard many good sounding inductors only because of their excessive sensivity to vibrations of the foot pedal treadle travel and footswich activation.

I should also mention the sensivity to hum induction : stages are often hum ridden, so an inductor may be influenced, making your rig unpleasantly humming. I had some problems too with that.

Any value from 0.2 to 2H and 15 to 100 ohms should be tested, from my experience. With tweaking the rest of the circuit of course !

A+!

[Paul Marossy]

Yeah, some inductors I have found can be pretty microphonic. 

They are also prone to noise like a single coil pickup is. Around 7 or 8 years ago now when I still kind of new at this stuff, I had a major hum from hell whenever I used my wah pedal and my Boss Metal Zone (for singing leads only) and I was baffled. Then I had a thought to move the wall wart to the opposite corner of the pedalboard and the problem completely went away. Problem was that the wall wart was only a few inches away from the wah pedal, so it was inducing a hum into the wah pedal even though all that circuitry is inside what is supposed to be a shielded enclosure. It didn't hum when using a "clean" sound because it didn't amplify that hum enough for it to be heard. But with that Metal Zone, it amplified the heck out of that hum. That was a learning experience anyway.

[Earthscum]

I never participated in the wah inductor debates because I didn't know how to approach it without getting "Pics or it didn't happen", lol... I have breadboarded wahs using everything from switchmode power supply filter parts, filter inductors from a car stereo amp, 42TM019 primary, and a whole handful of whatzits inductors. Each one was able to wah, and each had it's own sound to it, although it seemed that most were, to my ears, able to be tweaked to sound similar enough. The powdered ferrite core inductors did give a different sound than the si/iron lam. The laminated cores had more bite to them, it seemed, but that may have been my selection was so skewed (wire gauges from about 32 all the way up to about 18 or so).

But, nonetheless, I can vouch for others claims that the inductor seems to be a fairly minor part when it comes to great tone. That's MY opinion, though, lol.

[Paul Marossy]

I never participated in the wah inductor debates because I didn't know how to approach it without getting "Pics or it didn't happen", lol... I have breadboarded wahs using everything from switchmode power supply filter parts, filter inductors from a car stereo amp, 42TM019 primary, and a whole handful of whatzits inductors. Each one was able to wah, and each had it's own sound to it, although it seemed that most were, to my ears, able to be tweaked to sound similar enough. The powdered ferrite core inductors did give a different sound than the si/iron lam. The laminated cores had more bite to them, it seemed, but that may have been my selection was so skewed (wire gauges from about 32 all the way up to about 18 or so).

But, nonetheless, I can vouch for others claims that the inductor seems to be a fairly minor part when it comes to great tone. That's MY opinion, though, lol.

I could see how different core materials can be somewhat of a factor in the sound, probably because that affects the "Q". You know, the only purpose of the inductor is to make it a resonant circuit, it's not even in the signal path. As a manufacturer, you could fairly easily compensate for differences in inductors sourced from various vendors by simply changing a couple of parts. I think the idea from the manufacturer's point of view is to get a consistent sound out of their product, not to have a perfect inductor (because there is no such thing).

I have found that I can get pretty much the same sound out of whatever wah pedal I am using, so all this hype about inductors really is meaningless for me. In other words, I sound like me whatever wah pedal I use. I just adapt my technique slightly to get the sound I want, different pot tapers don't bother me none at all. Or I adjust the tone control on my guitar, etc. It's very natural for me.

[joegagan]

just a theory:
taper matters more than one might think. think of it like the shelf width on a parametric EQ, the two sides of the pot are actually interacting with a time element due to the charge and discharge of the cap to ground off inductor. as the pot passes through its travel, there are possibly real effects on the balancing act between the two transistors. an abrupt taper may cross the sweet spot so fast that the cap may not be charging and charging in the same way it would with a slower resistance change. i have a feeling that is why the  value ( 25k) and taper of a boomerang pot makes that circuit feel so much different to the player than a crybaby /vox. if you've played a stock boomerang with the correct type pot, you may have noticed a long sweet spot in the low mids. tony joe white and jj cale make really good use of this in their leads - both boomerang users.

[gmoon]

That's because you have to look at the circuit as a whole. The only thing that the inductor does in a wah is makes it a resonant circuit, it's not THE component that gives the wah pedal its sound like everyone wants to believe. There's a whole lot of other factors involved, too. The inductor is just one piece of the pie.

Paul, keep on fighting the good fight.

RE: I didn't measured the Q factor of this one, in order to compare it to "official" inductors : it probably have an undisclosed importance...

Just my two cents--inductors don't have a "Q" factor. Resonant circuits do, but inductors do not.

Inductors exhibit reluctance, reactance, hysteresis, impedance, have cores with a certain permeability, etc. All that stuff effects their operation (and their sound in a circuit), are speced upfront by the designers, but are difficult to measure after the fact. Yeah, they are an "X factor" because there are more variables than in caps or resistors. But the other components in the circuit matter a great deal (as does their value/tolerance). And then there's that whole subjective thing...

But I applaud anyone who's plugging in oddball inductors and mucking about with those stock-circuit wahs. Of course, that could lead to the ultimate in mojo (real or imagined  )--because it's near impossible to get the same 1950s oddball coil as someone else dug up...

[Paul Marossy]

Just my two cents--inductors don't have a "Q" factor. Resonant circuits do, but inductors do not.

Inductors exhibit reluctance, reactance, hysteresis, impedance, have cores with a certain permeability, etc. All that stuff effects their operation (and their sound in a circuit), are speced upfront by the designers, but are difficult to measure after the fact. Yeah, they are an "X factor" because there are more variables than in caps or resistors. But the other components in the circuit matter a great deal (as does their value/tolerance). And then there's that whole subjective thing...

Right, an inductor is not going to have a "Q" factor until it's in a circuit. So if you pull out one inductor and replace it with another one, it will probably sound a little different because of its affect on the "Q". That's why my earlier statement of the manufacturer wanting to have consistency when sourcing inductors from various vendors and changing some parts - like the "Q" resistor for example being different in some of the original Clyde McCoys. But as the years progressed, their available inductors changed, transistors changed, etc. and little tweaks had to be made to the circuits to make them sound good to their ears - which also changes along with the personnel. What sounded good to the people that made the things in 1967 is not the same as it is in 2011 because people's tastes change.

So people today look at the current CryBaby for example with the typical inductor measuring 660mH and think that it sucks because it doesn't measure EXACTLY 500mH with EXACTLY some DC resistance. But if you look at the rest of the circuit, it's a very different animal than the original wah pedals which were all over the map because of variability in parts, tolerances, etc. and designwise (ie no input buffer). So it's hard to compare apples with apples because they are just not the same. And it has been demonstrated that inductors between 500mH to over 1H can all sound good and function as intended.

Anyway, I don't buy these stories of when someone changed their inductor and it was a night and day difference. Of course, in their mind, it was because of that whole physoacoustic phenomenon thing people so often exhibit.

[tubelectron]

Hi gmoon,

RE: I didn't measured the Q factor of this one, in order to compare it to "official" inductors : it probably have an undisclosed importance...

Just my two cents--inductors don't have a "Q" factor. Resonant circuits do, but inductors do not.

Q = 2.PI.F.L / R = X (reactance) / R (resistance)

Where :

Q = surtension factor, or "quality factor" (the opposite to the damping factor)
PI = 3.14etc...
F in Hz
L in Henry
R in ohms

My old RLC bridge measures inductor's Q from 0.1 to 1000, along with D for capacitors (which represent a"loss factor")

The Q of the inductor influences the resonance curve and peak of the tuned circuit, and so the Q of the whole (like D would). An higher Q inductor would probably give a sharpier wah, or more vocal, in any way an accentuated wah effect, if F is adequate.

A+!

[gmoon]

Hi, tubeelectron

You are absolutely right--in a practical sense. 'Cause a real inductor has internal resistance, unlike an "ideal inductor."

When you're testing the "Q" of L, you're testing LR as a resonant circuit. And that Q won't be the same as the Q in the wah circuit... But it certainly could be useful info.

Sorry, I misspoke.

[Brymus]

Well I agree with alot of this.
Microphonic inductors,yep some are almost microphones themselves.

Magic inductor,sure if it fits the circuit,it can sound great by comparison.

My big amazement was how a handful of pots (same value) some the same lot ,a few of different manufacture,
Could sound so different.
One of the "cheap" wah pots actually made the circuit sound great and that was that.

One of the pots that sounded awful, sounded great if I added another inductor in series.
So its not cut and dry.

[tubelectron]

One of the "cheap" wah pots actually made the circuit sound great and that was that.

That's right - I would say that there is also "pots from scratch" like "inductors from scratch" : random value, LIN, LOG or weird taper... You may find one pot which suits exactly your needs, even if it is very far from the "official" pot specs. The drawback is, when it fails, replacement is not guaranteed to be easy...

For instance, one of my vintage wah uses a LOG 60,4K sealed Allen Bradley pot from WWII stock... Fortunately abuse-resistant !

I have 2 japanese wah from the early 70's on which the pots are 100K LIN, and the pinion has a set screw, making then the replacement non-critical.

A+!

[joegagan]

most of the shin-ei made wahs i have seen contain a 50k audio sealed pot. they are quite durable actually.