Dummy Coils - Theory help (then maybe application)

freefrog

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Starting on the theory side...

I thought I understood how a humbucker worked... two coils, one reverse would, back to back. Hum generated by both coils with opposite hum/sine waves, sine waves cancel each other (always wondered why this didn't cause the canceling of other frequencies that I want, like the notes I play, but that's a side question/tangent).

I also know that you can have the same arrangement with two single coils and one RWRP forming an extended humbucker on a two-pickup, single coils guitar.

My issue: I thought that in either case the magnetic coils needed to be in physical alignment for it to work. Same plane, rough physical proximity, just one coil RWRP. But, as I've started to look into using a dummy coil (no magnets or core), I've seen them stuffed in all sort of locations with little concern about physical placement/alignment.

So, first question: Does the humbucking effect work simply by having the RWRP in the circuit? Would it work the same (as an example) if I stuck the dummy coil in a non-metal box with a couple jacks and plugged into the box from the guitar and then went to the amp?

Second question: Let's assume you have a humbucker or two single coils (one RWRP) already doing humbucking. You put a dummy coil in the line. Does the dummy now re-generate hum that your humbuckers filtered out?
Lester,

I haven't replied immediately to your questions 'cause I wanted to do a funny il' test for ya. Not that I've too much free time but it took me only five minutes this evening....

Below is the trace of a recording involving my Hamer with P90's, through a Tube Screamer feeding a tube distortion. Each pedal had its gain knob @ noon and the amp was set clean.
The first part translates the noise produced by the P90 neck alone in this case.
The second part is with the dummy coil enabled.
The third part is with the dummy coil flipped upside down in the guitar (I had to put the recording on "pause" and to pull off three screws for that).
The fourth part shows what happens when the dummy coil is oriented in the right direction but located outside the guitar.
The fifth part is with the dummy coil perpendicular to the guitar.
The last part shows what happens when the dummy coil is "angled" (IOW: not parallel nor perpendicular) outside the guitar.

I've put back the dummy coil in its initial place. But I hope this experiment to reply to your first question...

P90&dummyCoil.jpg


And yes, the reply to your Q2 is yes. :)

HTH.

See ya!
 

Lester

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Lester,

I haven't replied immediately to your questions 'cause I wanted to do a funny il' test for ya. Not that I've too much free time but it took me only five minutes this evening....

Below is the trace of a recording involving my Hamer with P90's, through a Tube Screamer feeding a tube distortion. Each pedal had its gain knob @ noon and the amp was set clean.
The first part translates the noise produced by the P90 neck alone in this case.
The second part is with the dummy coil enabled.
The third part is with the dummy coil flipped upside down in the guitar (I had to put the recording on "pause" and to pull off three screws for that).
The fourth part shows what happens when the dummy coil is oriented in the right direction but located outside the guitar.
The fifth part is with the dummy coil perpendicular to the guitar.
The last part shows what happens when the dummy coil is "angled" (IOW: not parallel nor perpendicular) outside the guitar.

I've put back the dummy coil in its initial place. But I hope this experiment to reply to your first question...

View attachment 538922

And yes, the reply to your Q2 is yes. :)

HTH.

See ya!
Frog: Thanks for all the info... but did some graphics get left out?

FYI - I've piloted a bass filter on this, per your suggestions in other threads. I'm curious to see what the dummy coil does comparatively / additionally to that with some top end filtering while it potentially cuts noise. The bass filter does a great job of cleaning up the lower end mud when using distortion. Back to crisp. But, I think I bought it down to just one setting that will be on/off on a push pull for this guitar. Mud and no mud.
 
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Roger66

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Hi Free Frog, sorry I got that wrong. So the #2 trace is the dummy coil next to the pickup, right? That has the least hum, correct? Thats what I see. And it's a P90. With alnico magnets instead of stock. That makes up for the tone loss from th dummy coil, right? Am I to conclude that making the magnet stronger makes up for the dummy coil or did I get it wrong. It seems plausible. So through trial and error I could find the right extra or stronger magnet to add to a pickup with a dummy coil to get it back up to par? I'm trying to get my puny brain around this and I totally appreciate your wisdom. Oh and is the dummy coil in parallel or in series. I would have thought parallel, but I want to learn.
Thanks
 

Roger66

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Hi Free Frog, sorry I got that wrong. So the #2 trace is the dummy coil next to the pickup, right? That has the least hum, correct? Thats what I see. And it's a P90. With alnico magnets instead of stock. That makes up for the tone loss from th dummy coil, right? Am I to conclude that making the magnet stronger makes up for the dummy coil or did I get it wrong. It seems plausible. So through trial and error I could find the right extra or stronger magnet to add to a pickup with a dummy coil to get it back up to par? I'm trying to get my puny brain around this and I totally appreciate your wisdom. Oh and is the dummy coil in parallel or in series. I would have thought parallel, but I want to learn.
Thanks
It sure was nice of you to do those experiments and showing the traces for us.
 

Roger66

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Wouldn't a box that generated a 60hz and/or 120hz, mix of sine waves that is adjustable as to phase, gain, clipping, and 60hz / 120hz balance be able to dial out just about any hum one would encounter?
One could have a deluxe model that would do 55hz and 110hz for foreign gigs and maybe a third adjustable frequency for other types of interference. Maybe adapt a noise cancelling headphone circuit and adjust it to your particular hum? Then feed the cancellation 'anti-hum' back into your signal? Seems plausible to me. Any opinions?
 

freefrog

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Lester,
I've omitted to add graphic separators between parts but all are there. The dummy coil just makes very little to no difference when it's not oriented properly (or increases the noise when flipped upside down).

Roger66,
-The second trace is with the dummy coil inside the shielded cavity (not immediately next to the pickup in this case but oriented in the same direction).
-P90's with AlNiCo rods are those in the Blueshawk. As I said in a previous post, they have more "touch sensivity" thx to their stronger magnets and compensate the "inertia" of the dummy coil. They have also less inductance than a regular P90 with ferrous parts so the higher inductance due to a dummy coil in series is less a problem. JT Riboloff (the engineer behind the Blueshawk) did know his stuff. See there: https://blueguitar.net/new/schem/_gtr/blueshawk_circuitry.pdf
-It's not a safe project to put AlNiCo rods in a normal P90: The bobbin would have to be drilled for that. But some companies sell such pickups "ready made" (see "Fleor", for instance: there was a thread about that recently).
-In MY guitar, there's regular P90's with a lil' custom circuit of mine: as I said in a reply above, my goal was to obtain the tone of minihumbuckers once the dummy coil enabled.
-The dummy coil is in series in my Hamer as it is in my "spare" Strat or in a Blueshawk. It would be possible to wire it in parallel... but it would divide the DCR and inductance (by two approximatively and in a non controlable way). The sound would get weaker and brighter.
Now in a STRAT or TELE with STRONG single coils (in the 13k range) a 13k dummy coil in parallel would be interesting since it would lower resistance and inductance to the "normal" values of a 6.5k transducer... The slight loss of volume could/should then be compensated by setting the pickup a bit closer to the strings.
But that's all theory: nothing is worth trail and errors (reason why I rarely mount twice the same circuit in two different guitars). :)
 
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Lester

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Frog: Thanks. I was looking at that data completely incorrectly. Got it now.

On the orientation: you're confident it was the relationship to the other pickups vs the source of the hum based on how you did the tests here or previously? The reason I ask is that the hum I get can be decreased 90% by turning 90 degrees. I am fairly certain my local hum is coming from the power lines nearby. If I get perpendicular to them it almost vanishes. Just wondering if that's accounted for at your end.
 

freefrog

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Frog: Thanks. I was looking at that data completely incorrectly. Got it now.

On the orientation: you're confident it was the relationship to the other pickups vs the source of the hum based on how you did the tests here or previously? The reason I ask is that the hum I get can be decreased 90% by turning 90 degrees. I am fairly certain my local hum is coming from the power lines nearby. If I get perpendicular to them it almost vanishes. Just wondering if that's accounted for at your end.
Hello,

In my test, the position of the guitar relatively to the "noise source" (a lamp next to a computer screen) was strictly the same. I've changed ONLY the position of the dummy coil in the guitar or next to it.

That said: yes, of course, we can tame the hum by giving a different position / angle to a guitar relatively to a "noise source". That's a well known technique for single coils players when they record - but not really useable on stage, sadly. ;-))

For the record, this question of angle can be a problem as well as a solution even with humbuckers... and it's the main weakness of the "Ilitch air coil" (or of any dummy coil) when it's not mounted strictly on the same plan than the pickups: in some positions, the guitar can get noisy despite of a dummy coil if for example this dummy coil is mounted on the back of the instrument.

Life is made of compromises... :)

See you later, I'm a bit busy right now.
 

Lester

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Hello,

In my test, the position of the guitar relatively to the "noise source" (a lamp next to a computer screen) was strictly the same. I've changed ONLY the position of the dummy coil in the guitar or next to it.

That said: yes, of course, we can tame the hum by giving a different position / angle to a guitar relatively to a "noise source". That's a well known technique for single coils players when they record - but not really useable on stage, sadly. ;-))

For the record, this question of angle can be a problem as well as a solution even with humbuckers... and it's the main weakness of the "Ilitch air coil" (or of any dummy coil) when it's not mounted strictly on the same plan than the pickups: in some positions, the guitar can get noisy despite of a dummy coil if for example this dummy coil is mounted on the back of the instrument.

Life is made of compromises... :)

See you later, I'm a bit busy right now.

Thanks again. I'll get to experimenting.
 

Roger66

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Lester,
I've omitted to add graphic separators between parts but all are there. The dummy coil just makes very little to no difference when it's not oriented properly (or increases the noise when flipped upside down).

Roger66,
-The second trace is with the dummy coil inside the shielded cavity (not immediately next to the pickup in this case but oriented in the same direction).
-P90's with AlNiCo rods are those in the Blueshawk. As I said in a previous post, they have more "touch sensivity" thx to their stronger magnets and compensate the "inertia" of the dummy coil. They have also less inductance than a regular P90 with ferrous parts so the higher inductance due to a dummy coil in series is less a problem. JT Riboloff (the engineer behind the Blueshawk) did know his stuff. See there: https://blueguitar.net/new/schem/_gtr/blueshawk_circuitry.pdf
-It's not a safe project to put AlNiCo rods in a normal P90: The bobbin would have to be drilled for that. But some companies sell such pickups "ready made" (see "Fleor", for instance: there was a thread about that recently).
-In MY guitar, there's regular P90's with a lil' custom circuit of mine: as I said in a reply above, my goal was to obtain the tone of minihumbuckers once the dummy coil enabled.
-The dummy coil is in series in my Hamer as it is in my "spare" Strat or in a Blueshawk. It would be possible to wire it in parallel... but it would divide the DCR and inductance (by two approximatively and in a non controlable way). The sound would get weaker and brighter.
Now in a STRAT or TELE with STRONG single coils (in the 13k range) a 13k dummy coil in parallel would be interesting since it would lower resistance and inductance to the "normal" values of a 6.5k transducer... The slight loss of volume could/should then be compensated by setting the pickup a bit closer to the strings.
But that's all theory: nothing is worth trail and errors (reason why I rarely mount twice the same circuit in two different guitars). :)
Ok, Free Frog, TH? THE IDEA I HAD, oops, caps lock.
Ahem, the idea I had was making the magnets stronger by putting a strong magnet under the pole magnets maybe a rare earth magnet. I have some 1mm. thick by 3-6 mm diameter rare earth magnets, I have been dying to use. I normally use them for intricate stash boxes with magnetic keys. I will click on the link that you supplied
Thank you for all the information you provided. That was very nice of you.
 

Lester

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Ok, Free Frog, TH? THE IDEA I HAD, oops, caps lock.
Ahem, the idea I had was making the magnets stronger by putting a strong magnet under the pole magnets maybe a rare earth magnet. I have some 1mm. thick by 3-6 mm diameter rare earth magnets, I have been dying to use. I normally use them for intricate stash boxes with magnetic keys. I will click on the link that you supplied
Thank you for all the information you provided. That was very nice of you.

Roger: The usual path with the dummy coil is that it's just a coil - no magnets at all.
 

ErictheRed

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Wouldn't a box that generated a 60hz and/or 120hz, mix of sine waves that is adjustable as to phase, gain, clipping, and 60hz / 120hz balance be able to dial out just about any hum one would encounter?
One could have a deluxe model that would do 55hz and 110hz for foreign gigs and maybe a third adjustable frequency for other types of interference. Maybe adapt a noise cancelling headphone circuit and adjust it to your particular hum? Then feed the cancellation 'anti-hum' back into your signal? Seems plausible to me. Any opinions?
For many reasons, no. The generator would have to continually and dynamically change to match the amplitude of the noise source as well as the staying 180 degrees out of phase. On top of that difficulty, you'd have a ground loop and common mode voltage and higher order harmonics to deal with, and other things.

Noise cancelling headphones have microphones that capture the noise signal, then a preamp circuit, then an analog digital converter to sample the signal, then a microprocessor to do the calculations, then a signal generator to create the proper waveform...you want all of that in a guitar cable? That is then going to be amplified in the guitar amp? It would just create a ton more noise, even if it eliminated the noise that you wanted it to.
 
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Roger66

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For many reasons, no. The generator would have to continually and dynamically change to match the amplitude of the noise source as well as the staying 180 degrees out of phase. On top of that difficulty, you'd have a ground loop and common mode voltage and higher order harmonics to deal with, and other things.

Noise cancelling headphones have microphones that capture the noise signal, then a preamp circuit, then an analog digital converter to sample the signal, then a microprocessor to do the calculations, then a signal generator to create the proper waveform...you want all of that in a guitar cable? That is then going to be amplified in the guitar amp? It would just create a ton more noise, even if it eliminated the noise that you wanted it to. Thanks for thinking that through
Well, I was thinking about putting it in a stomp box, but not anymore, lol. Thanks for schooling me on that! I know enough to build an amp, but that's easy compared to what I came up with. Yeah, dummy coils and shielding is the way to go. A little knowledge is a dangerous thing. Yeah. I was thinking as well that if my crazy scheme worked, someone else would have done it already. I thought I saw a box in the SW catalog that claims to eliminate hum. Do you know about that thing? Thanks.
 

ErictheRed

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Well, I was thinking about putting it in a stomp box, but not anymore, lol. Thanks for schooling me on that! I know enough to build an amp, but that's easy compared to what I came up with. Yeah, dummy coils and shielding is the way to go. A little knowledge is a dangerous thing. Yeah. I was thinking as well that if my crazy scheme worked, someone else would have done it already. I thought I saw a box in the SW catalog that claims to eliminate hum. Do you know about that thing? Thanks.
There are noise suppressors and noise gates (different things) that can eliminate hum. It depends on the source and type of noise, but generally you want well isolated power strips for the AC outlet, an isolated regulated DC power supply for the pedals, properly shielded and grounded guitar (no ground loops), properly shielded instrument cables, etc.

Me personally, I would start with the wiring on the guitar, then shield the guitar, then get good instrument cables, then isolated power supplies. If you still have noise issues, look into a noise suppressor and/or noise gate.
 

Roger66

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Yeah, that's how I feel. I have all that. And I have no hum problems at all. Yeah, that's the deal. A lot of people do have hum problems, but I learned all about dummy coils, from this thread, Which before, I felt were useless.
 

freefrog

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Ok, Free Frog, TH? THE IDEA I HAD, oops, caps lock.
Ahem, the idea I had was making the magnets stronger by putting a strong magnet under the pole magnets maybe a rare earth magnet. I have some 1mm. thick by 3-6 mm diameter rare earth magnets, I have been dying to use. I normally use them for intricate stash boxes with magnetic keys. I will click on the link that you supplied
Thank you for all the information you provided. That was very nice of you.
Delayed answer (been too busy the past days).

If you use rare Earth mags instead of AlNico bars in a P90, you might have to pull off the "keeper bar" below the coil and to shorten the screw poles by cutting them. Reasons:
-the probable north / south polarization of such mags is not meant to cooperate with the physical structure of P90's (requiring theoretically north and south poles on the edges of rectangular mags and not on their flat wide sides);
-the requested inductive value... if you keep much "ferrous content" as a core of the coil, the inductance won't drop as much as desired. Shortening the screw poles should be a step in the right direction (been there, done that, FWIW). In the same intent, you might have to use "non magnetic" height screws, made of brass for example.
Also, keep in mind that strong magnetism tends to create strings pull with the related effect ("stratitis", potentially) and might favor high pitched squealing if something is loose in the assembly.

That being said just to share, as usual.

Have fun in your experiments...
 
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DBDM

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https://www.wildepickups.com/ is the site run by the family of Bill Lawrence. This site is a complete wealth of information about how pickups work. There is not just one place where he describes everything (that would be too easy) but if you look at his various diagrams and links, it is ALL on there. To me the most comprehensive real world description of how pickups work that I have personally ever read.

This single link to an article in Guitar Player Magazine is very good
https://www.wildepickups.com/blogs/news/bill-lawrence-and-his-teachings-article-from-guitar-player-magazine-dec-1975

Edit--this (somehow) competing site is also a treasure trove. In all honesty I get them mixed up. No clue why there are 2 sites but guessing there was a business deal or the name was sold or something like that
http://www.billlawrence.com/Pages/All_About_Tone.htm/Pickupology.htm
 
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