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Thread: Unmuddy my 'bucker or dramatic slug swap results

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    Unmuddy my 'bucker or dramatic slug swap results

    Last evening I decided for another experiment to my old MIK Ibanez that I hold as experimentation platform and for sentimetal values.

    The humbucker in question always suffered from loads of mud, limited articulation, bassy and uninteresting sound. I believe it was called Powersound and was made by Cort.

    So - I decided to change the pole pieces to something entirely different. The slug pole pieces seem like the most omitted part to be changed in a pickup, as it appears wrongly.

    The original slugs were probably some sort of carbon steel, the substitute is medium permeability non-conductive material. Love the results

    Swap results:
    - punchy
    - snappy as hell
    - actually some trebles
    - reacts dramatically to articulation
    - lots of output (feels very loud, didn't measure yet)

    Original:
    - mud
    - mud
    - some more of the same

    Is it really that the most crucial part of the pickup is the most misunderstood and most overlooked one?

    Sound samples to come later on, stay tuned

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    What "medium permeability non-conductive material" did you use? Results sound interesting. I'd like to un-mud some pickups I have on a Michael Kelly Hybrid.

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    Quote Originally Posted by cbarrow7625 View Post
    What "medium permeability non-conductive material" did you use? Results sound interesting. I'd like to un-mud some pickups I have on a Michael Kelly Hybrid.
    Technically it is a soft ferrite.

    Unlike 'hard' ferrite it needs an external permanent magnet to generate magnetic field - thus making it usable for humbucking design.

    Also unlike the power conversion ferrites, the ones you'd use in a choke or a SMPS transformer - it has a moderate permeability, comparable to that of carbon steel - thus not overwhelming the pickup with too much inductance.

    The interesting part of the pickup design now is that virtually no conductive elements are within the magnetic field (well, except the string maybe), making the pickup completely free from any sort of eddy current losses.

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    Quote Originally Posted by darkfenriz View Post
    Technically it is a soft ferrite.

    Unlike 'hard' ferrite it needs an external permanent magnet to generate magnetic field - thus making it usable for humbucking design.

    Also unlike the power conversion ferrites, the ones you'd use in a choke or a SMPS transformer - it has a moderate permeability, comparable to that of carbon steel - thus not overwhelming the pickup with too much inductance.

    The interesting part of the pickup design now is that virtually no conductive elements are within the magnetic field (well, except the string maybe), making the pickup completely free from any sort of eddy current losses.
    The interesting part of the pickup design now is that virtually no conductive elements are within the magnetic field (well, except the string maybe), making the pickup completely free from any sort of eddy current losses.[/QUOTE]

    You are making it into a very different pickup. The eddy current loss in steel is the dominant loss mechanism in humbuckers. Ferrite can have essentially no loss, while Alnico comes somewhere in between. I have used ferrite rods in various pickup designs with good success. I get them from Amidon.

    One thing about permeability and pickups: Pickups are open magnetic circuits; Some people say "the air gap dominates". This is in contrast to magnetic circuits such as used in transformers in which the magnetic material forms a closed path. In open magnetic circuits, the inductance does not continue to increase with increasing permeability for greater than about ten or so. Thus, 100 or 3000 does not make much difference. This is generally true for components in open circuits. For example, you can find MacDonald's derivation (Princeton professor) regarding how pickups work, and he shows that the value of the permeability of the string does not matter as long is not small.

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    Quote Originally Posted by darkfenriz View Post
    Technically it is a soft ferrite.

    Unlike 'hard' ferrite it needs an external permanent magnet to generate magnetic field - thus making it usable for humbucking design.

    Also unlike the power conversion ferrites, the ones you'd use in a choke or a SMPS transformer - it has a moderate permeability, comparable to that of carbon steel - thus not overwhelming the pickup with too much inductance.

    The interesting part of the pickup design now is that virtually no conductive elements are within the magnetic field (well, except the string maybe), making the pickup completely free from any sort of eddy current losses.
    So the inductance probably changed, to some degree, maybe not a lot. If it was reduced, that would "de-mud" it. Do you have a good LCR meter?

    Also, the lack of eddy currents, as you mentioned, means a higher Q factor. While, that increases treble response, the way in which a high Q factor puts a strong emphasis on a particular frequency band is almost a "defect" in its own right. The fact that you rarely see a no load tone pot and a 1meg volume in a guitar for maximum Q factor speaks to the fact that guitarists might like some, but not a lot of resonance. If you like it, so much the better, but as a rule or thumb, if the Q factor went way up, you might have to put a few hundred k ohms of resistance across it to return the Q back to something palatable.

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    Quote Originally Posted by Antigua View Post
    So the inductance probably changed, to some degree, maybe not a lot. If it was reduced, that would "de-mud" it. Do you have a good LCR meter?

    Also, the lack of eddy currents, as you mentioned, means a higher Q factor. While, that increases treble response, the way in which a high Q factor puts a strong emphasis on a particular frequency band is almost a "defect" in its own right. The fact that you rarely see a no load tone pot and a 1meg volume in a guitar for maximum Q factor speaks to the fact that guitarists might like some, but not a lot of resonance. If you like it, so much the better, but as a rule or thumb, if the Q factor went way up, you might have to put a few hundred k ohms of resistance across it to return the Q back to something palatable.
    Yes, the Q factor shooting through the sky was goal indeed, I even removed the baseplate and used a piece of wood there, in the hindsight that maybe was not the most clever thing to do, at least not the most efficient in terms of boosting Q.

    I don't know what's your background, but for me there's no such thing as too much Q to start with - I mostly use hot humbuckers and never touch the tone control on the guitar. Your comments may be more applicable to vintage single coils.

    For the record all the tone control on the guitar does is just descreses the Q of the pickup at the top of the potentiometer range. Killing the Q is easy.

    On the contrary - I've seen loads of hot humbuckers users in all the 'superstrat', 'metal' or 'shred' guitars never touching the guitar tone control. Must be fun reinventing the knob at some point.

    As for L - I tend to measure indirectly with the scope and a known cap and finding the resonant peak, but I admit not doing it this time. Anyway - the cable C is just as much responsible for the resonance frequency and it will vary fromcable to cable like crazy...

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    Quote Originally Posted by darkfenriz View Post
    I don't know what's your background, but for me there's no such thing as too much Q to start with - I mostly use hot humbuckers and never touch the tone control on the guitar. Your comments may be more applicable to vintage single coils.
    If you like a high Q factor, have you considered just using higher resistance pots?

    Quote Originally Posted by darkfenriz View Post
    As for L - I tend to measure indirectly with the scope and a known cap and finding the resonant peak, but I admit not doing it this time. Anyway - the cable C is just as much responsible for the resonance frequency and it will vary fromcable to cable like crazy...
    I wouldn't say the capacitance varies like crazy. Most guitarists use either a 10ft or 15ft guitar cable, with about 40pF per foot, give or take, so pickups on the market tend to maintain a reputation for being particularly bright or dark, vintage or hot, in direct relation to their inductance, through many different rigs and guitar cables. I don't know how much your replacement slugs varied the inductance, but if it was and extreme change, that would definitely have practical consequences.

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    Quote Originally Posted by Mike Sulzer View Post
    You are making it into a very different pickup. The eddy current loss in steel is the dominant loss mechanism in humbuckers. Ferrite can have essentially no loss, while Alnico comes somewhere in between. I have used ferrite rods in various pickup designs with good success. I get them from Amidon.
    Sure, but I wouldn't know if I didn't try It never ceases to amaze me when practice confirms the theory.

    What's amusing is how easily and cheaply I turned a horrible humbucker (paperweight range) into an insteresting one. After some playing, the second day to be specific, I think I hugely prefer it to the DiMarzio I have in the other guitar, if that a fair comparison (different guitar, diy-bias).


    Quote Originally Posted by Mike Sulzer View Post
    One thing about permeability and pickups: Pickups are open magnetic circuits; Some people say "the air gap dominates". This is in contrast to magnetic circuits such as used in transformers in which the magnetic material forms a closed path. In open magnetic circuits, the inductance does not continue to increase with increasing permeability for greater than about ten or so. Thus, 100 or 3000 does not make much difference. This is generally true for components in open circuits. For example, you can find MacDonald's derivation (Princeton professor) regarding how pickups work, and he shows that the value of the permeability of the string does not matter as long is not small.
    Thanks a lot- very informative.
    I think of the magnetic path of a humbucker as of one set of polepieces, the magnet, the other set of polepieces and the string, so nearly a closed path with two small-ish gaps. I reckon the permeablities are sort of like in parallel, so probably as you say it does not matter much if the polepiece is of permeability of 500 or 5000.
    I would also wonder whether the inductive coupling between the two coils is any factor here.
    Got the link to MacDonald's work?

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    Last edited by darkfenriz; 01-21-2018 at 12:46 AM.

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    Quote Originally Posted by Antigua View Post
    If you like a high Q factor, have you considered just using higher resistance pots?
    I tried 1Meg volume with tone just snapped, I tried bypassing all that and just using the killswitch and I tried increasing the amp's input impadance to some 20Meg (jfet opamp with input boostrap trick).
    It did help somewhat, but not much and left me wanting more.

    My understanding is carbon steel pole pieces at 5mm diameter must be very lossy if the material is chosen carelessly, i.e. both highly permeable and highly conductive. Hard to restore the Q once it is killed at source.

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    Quote Originally Posted by darkfenriz View Post
    Thanks a lot- very informative.
    I think of the magnetic path o a humbucker as of one set of polepieces, the magnet, the other set of polepieces and the string, so nearly a closed path with two small-ish gaps. I reckon the permeablities are sort of like in parallel, so probably as you say it does not matter much if the polepiece is of permeability of 500 or 5000.
    I would also wonder whether the inductive coupling between the two coils is any factor here.
    Got the link to MacDonald's work?

    I know this isn't a reply to me but I can save some trouble, this is the Kirk McDonald pdf http://www.physics.princeton.edu/~mc...les/guitar.pdf

    Regarding the air gaps, in magnetic circuit design terms, they're absolutely huge. When they intentionally put air gaps in a transformer core, it's usually something small like this:
    Click image for larger version. 

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    The guitar string is so thin that it does almost nothing to close the gap, and on the underside you have the AlNiCo, which has a rather low permeability, so it's not a lot better.

    There's been some tests done on inductive coupling between the coils, and there is capacitive coupling as well, but if memory serves, neither is too significant. It becomes an issue when you split a humbucker, and you decide on whether the second coil is shunted, left open, or fully disconnected at both ends, so that it won't couple with the active coil as much. IIRC, it's not even worth distinguishing between the different split modes in practice.

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    Quote Originally Posted by darkfenriz View Post
    I tried 1Meg volume with tone just snapped, I tried bypassing all that and just using the killswitch and I tried increasing the amp's input impadance to some 20Meg (jfet opamp with input boostrap trick).
    It did help somewhat, but not much and left me wanting more.
    1 meg pots left you wanting more treble? It almost sounds like there is an underlying problem somewhere that is causing treble losses beyond what is ordinary.

    Quote Originally Posted by darkfenriz View Post
    My understanding is carbon steel pole pieces at 5mm diameter must be very lossy if the material is chosen carelessly, i.e. both highly permeable and highly conductive. Hard to restore the Q once it is killed at source.
    Your typical humbucker doesn't completely kill the resonance. A combination of steel core and a cheap brass cover can, though. I'm not sure what you mean about the material being chosen carelessly, what would be an example of that?

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    Where is the pickup located?
    When talking muddy humbucker, usually it is a neck humbucker pickup.
    On a PAF type pickup, to get a brighter pickup?
    Baseplate type, nickel is brighter than brass.
    Magnet type, A2, A3 or A5? Ceramics sound a bit different.
    Main factor is to not overwind the coils.
    I like less than 5000 turns per coil, for a neck pickup.
    The further the neck pickup is from the bridge, less turns.
    Pots, usually 500k.
    Caps, .022-.047uf
    T

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    “When you find yourself in a hole, quit digging.” WILL ROGERS

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    The humbucker in question is powersound ibanez in neck position. It doesn't seem to have many fans.

    I believe it is a flawed design to start with - it combines high overwinding with 12 steel slugs, each 5mm (0.2") - contrary to typical (at least) one set of screws, which are typical smaller in diameter and contribute less to eddy current losses.

    Not sure about the carbon content of the slugs, but it started corroding pretty fast - and as far as I remember the fast corroding steels are also those with high permeability, which means low skin depth, which means big eddy current losses.

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    Supporting Member Steve A.'s Avatar
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    I find it very interesting that with all of the concern over the composition of pickup magnets there has not been a lot of interest in swapping out humbucker slugs, other than the different varieties of carbon steel which are discussed in the following links. I guess that anyone interested in experimenting could get a metal rod of appropriate diameter and use a dremel tool to slice off the slugs and chamfer the cut edges.

    http://music-electronics-forum.com/t26234/

    http://music-electronics-forum.com/t21609/

    https://www.seymourduncan.com/forum/...nd-pole-pieces

    Any suggestions on removing the slugs? I guess that a faucet knob removal tool might work if they don't push out easily with a screwdriver...



    https://www.homedepot.com/p/Faucet-H...X168/204218643

    Here is one suggestion from the Seymour Duncan forum...



    Thanks for bringing up an interesting topic!


    Steve A.

    P.S. Gibson has been putting double slug pickups in some of their recent guitars: the 2013 LPJ and SGJ using the 490T and 490R variations with the plastic covers and the 2017 M2 with import "probuckers" (reportedly not the same high quality as the ones used in recent Epiphones.) The M2 was Gibson's experiment in building a guitar in the US with imported hardware and electronics to keep the price down, originally $399 but raised to $499 when people started discovering how good they are.

    I hardly ever adjust the height of the humbucker screws on my guitars so pickups with double slug bobbins don't bother me — as long as they deliver the vintage-ish tones I prefer (no mega monstrosities for me!)

    It would be interesting to experiment with two slug bobbins with differerent composition slugs, starting with the different varieties of carbon steel and then moving on to different metals. Or as suggested in one of the earlier MEF threads to use different varieties of carbon steel for the wound and plain string slugs (IMO a lot of Gibson neck humbuckers have too much bass!)

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    I pay a lot of attention to screw and slug alloys -- they definitely matter. The typical over the counter stuff works fine for neck humbuckers but I used different stuff for most bridge models, more carbon. These days I make all my own slugs so I can control for the alloys. Wish I could make the screws...

    Obviously magnets also matter.

    All that said, I suspect the main problem with the OP's pickup is just a crummy wind -- too many turns, bad pattern, or overpotting. Or more than likely some combo of all three.

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    Quote Originally Posted by Zhangliqun View Post
    I pay a lot of attention to screw and slug alloys -- they definitely matter.
    There's some analysis of pickups out there, and general info about the significance of air gap with respect to the permeability of the core, that suggest that because such a large amount of the flux path is air, that the various permeabilities of these steel alloys can't stand to make much of a difference, at least not compare to AlNiCo, which has such a low permeability, that the degree to which it alters the inductance and the reluctance path is still worth distinguishing.

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    Junior Member Tone Cam's Avatar
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    Saturation effects can also contribute significantly to the tonal properties of soft ferrite slugs. Not sure what material you are working with but the high and medium perm ferrites that I have tried saturate significantly when you put them close to an alnico bar magnet. You can see if this is happening with the slugs you are using by disconnecting the slug coil from the pickup and looking at its isolated inductance with an LCR meter. If you then take a fully magnetized humbucker magnet and move it towards the slugs the measured inductance will decrease with distance if they are saturating. The percentage reduction gives a qualitative indication of how bad the saturation is.

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    Junior Member Tone Cam's Avatar
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    I am hoping there is still some interest in ferrite poles. I wasn't around when this thread first came up but am very interested in nontraditional pole materials.

    When I was first starting working on pickups I tried several different ferrite compounds. The tone was very clean due to their low ferromagnetic loss coefficients but I stopped working with them because their permeability seemed to saturate in the presence of low field magnetic fields. When I watched the inductance of a ferrite-loaded humbucker coil with an LCR meter, it would decrease significantly anytime I moved an Alnico magnet near the slugs. At the time I didn't think that saturation was good for tone.

    Did you guys see/hear saturation effects with your ferrites? If so, what do you think saturation does to the tone of a pickup?

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    When I was first starting working on pickups I tried several different ferrite compounds. The tone was very clean due to their low ferromagnetic loss coefficients but I stopped working with them because their permeability seemed to saturate in the presence of low field magnetic fields. When I watched the inductance of a ferrite-loaded humbucker coil with an LCR meter, it would decrease significantly anytime I moved an Alnico magnet near the slugs. At the time I didn't think that saturation was good for tone.
    This is a very interesting observation. And it shows that AC and DC permeabilities are two different and independent parameters. While the ferrite cores may still carry a substantial (DC or permanent) B and thus produce satisfactory Gauss values on their tops, the AC permeability (aka "reversible permeability") may drop from initial values of thousands down to just above 1 in the presence of a sufficiently high permanent field. (Something similar happens in the strings directly above the PU.)
    It is known from magnet literature that the AC permeability decreases with increasing DC fields. High µ ferrites are especially sensitive to this effect.
    Inductivity is influenced by the AC-µ of the cores and thus shows the change - albeit strongly alleviated by the airgap.

    Now if the AC-µ drops to very low values, two things happen. Firstly, inductivity drops by up to 30%, resulting in a higher rersonant frequency. Secondly, the poles lose their ability to collect and focus the AC flux (mainly concerning the returning part) created by the moving strings which should influence the effective aperture length.

    Soft ferrite pole PUs will show a comparatively strong sound dependance on magnet strength.

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    Quote Originally Posted by Helmholtz View Post
    Soft ferrite pole PUs will show a comparatively strong sound dependance on magnet strength.
    You're talking theory, but without any actual values, it's hard to say whether the effects are of a magnitude that permits it to be audible. In general, there's a lot of talk about theory, but not much hard data, so whether the rubber ever actually "meets the road" is not truly known. That's why I like gathering data, but test that involve exotic materials are harder to conduct.

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    Quote Originally Posted by Tone Cam View Post
    When I was first starting working on pickups I tried several different ferrite compounds. The tone was very clean due to their low ferromagnetic loss coefficients but I stopped working with them because their permeability seemed to saturate in the presence of low field magnetic fields. When I watched the inductance of a ferrite-loaded humbucker coil with an LCR meter, it would decrease significantly anytime I moved an Alnico magnet near the slugs. At the time I didn't think that saturation was good for tone.
    Were these soft ferrites that required an permanent magnet such as AlNiCo in order to function, or hard ferrites with their own sustained B field? How much did the inductance of the pickup drop compared to having air gapped coils, which is to wonder, how close would the ferrite come to unity when the AlNiCo bar was near?

    As for how this effects tone, there is a lot of vague talk on forums about how one factor or another impacts the "sound" or the "tone", but unless there is a time dependence aspect to that factor (like reactance), then the impact of that factor will be nearly or completely uniform with respect to frequency, resulting in little more than a variation in output voltage. A difference in output level itself might be perceived as a tonal change to some people's ears, but whether it should be considered such in a technical sense is another question.

    I think one factor that goes overlooked due to it's complexity, and the uniqueness of the problem domain, is precisely how string pull effects tone. It's possible that the B field over the ferrite poles either produces a particularly strong magnetic pull upon the strings, or a very weak pull. You'd need a gauss meter on hand to figure out which is the case, which can be had for about $100 these days. I think a lot of the strong opinions about things like magnetic strength and pickups height come down to personal preference with regard to magnetic interference upon the movement of the guitar strings, and it's possible that if you didn't like the outcome of ferrite poles, it might have something to due with that. Another reason the subject of string pull is so opaque is that, because the effects are so complex, effecting various harmonics in difference ways, differently depending on where the pickup is located, the difference in terms of tone is difficult to state in plain English. If you ask people how adjusting the height of pickups changes the tone, you will get a lot of different answers.

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    Last edited by Antigua; 07-26-2018 at 06:29 PM.

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    Quote Originally Posted by Antigua View Post
    You're talking theory, but without any actual values, it's hard to say whether the effects are of a magnitude that permits it to be audible. In general, there's a lot of talk about theory, but not much hard data, so whether the rubber ever actually "meets the road" is not truly known. That's why I like gathering data, but test that involve exotic materials are harder to conduct.
    Not really a factual comment.

    If you read my post carefully, you will find some valid data based on (own) measurements and soft ferrite data. I used to work with ferrites and especially analyzed saturation behaviour.
    A 10%-15% increase in resonant frequency is audible, at least to me.

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    Quote Originally Posted by Tone Cam View Post
    I am hoping there is still some interest in ferrite poles. I wasn't around when this thread first came up but am very interested in nontraditional pole materials.

    When I was first starting working on pickups I tried several different ferrite compounds. The tone was very clean due to their low ferromagnetic loss coefficients but I stopped working with them because their permeability seemed to saturate in the presence of low field magnetic fields. When I watched the inductance of a ferrite-loaded humbucker coil with an LCR meter, it would decrease significantly anytime I moved an Alnico magnet near the slugs. At the time I didn't think that saturation was good for tone.

    Did you guys see/hear saturation effects with your ferrites? If so, what do you think saturation does to the tone of a pickup?
    Your observation is obviuosly technically correct if you consider a strong () magnet in a humbucker with ferrite pole pieces.

    Ferrite pole pieces will typically saturate at below 400mT and start their saturation 'knee' around maybe 250mT.

    On the other hand alnico magnets will typically be 300-900mT (correction:30-90mT) strong while ferrite aka ceramic magnets are weaker (correction:stronger) at typically 200-350mT, some are weaker than that.

    So yes, the alnico magnet is (not) very likely to saturate ferrite pole pieces (same as) ceramic magnet (which I used).

    Regarding the pickup working at pole piece saturation I don't see that as a problem at all. After all this is what actually goes on with magnetized alnico slugs on a strat single coil.

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    Last edited by darkfenriz; 07-29-2018 at 08:08 AM.

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    Quote Originally Posted by darkfenriz View Post
    Your observation is obviuosly technically correct if you consider a strong alnico magnet in a humbucker with ferrite pole pieces.

    Ferrite pole pieces will typically saturate at below 400mT and start their saturation 'knee' around maybe 250mT.

    On the other hand alnico magnets will typically be 300-900mT strong while ferrite (aka ceramic) magnets are weaker at typically 200-350mT, some are even weaker than that.

    So yes, the alnico magnet is very likely to saturate ferrite pole pieces but ceramic magnet (which I used), well, not really, maybe a bit.

    Regarding the pickup working at pole piece saturation I don't see that as a problem at all. After all this is what actually goes on with magnetized alnico slugs on a strat single coil.
    Sorry, there seems to be some confusion of magnet units. 100mT correspond to 1000G. A fully charged alnico V bar magnet has around 800G= 80mT in the center of the pole faces. The ceramic bars I measured produced around 1400G=140mT and thus were considerably stronger than the alnicos.
    This said, there are many different ceramic magnet grades and virtually hundreds of different soft ferrite types.


    Regarding the pickup working at pole piece saturation I don't see that as a problem at all. After all this is what actually goes on with magnetized alnico slugs on a strat single coil.
    Completely agree. Good point, not the same but somehow comparable.

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    Last edited by Helmholtz; 07-28-2018 at 08:04 PM.
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  25. #25
    Junior Member Tone Cam's Avatar
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    I think that Helmholtz is correct about the units.

    Since my first post I have spent some time reading and doing tests.

    There is a lot of tech data out there from the ferrite manufacturers that directly addresses questions of saturation, frequency dependence, etc. (see, for example, https://www.mag-inc.com/Design/Techn...Core-Documents). There is also a pretty good book on the subject by Goldman (https://www.springer.com/us/book/9780387281513). When I looked through the data sheets I realized that the saturation flux varies over a significant range and many compounds have values greater than 3 kGauss. I also looked for a definition of saturation flux and found one at https://product.tdk.com/info/en/cont...ory=10_ferrite. Based on that definition and the associated hysteresis curve I would expect the inductance to roll off before you get to the tabulated value but that the rolloff should be small at fields below 1 kGauss in the compounds with the highest saturation flux values.

    I found some HB-sized rods in my box of old ferrites that did not show saturation behavior with an Alnico bar magnet. They showed a 10% reduction in inductance when I stuck a 3/16" tall stack of NdB discs on each pole but the fields generated by the discs (estimated from the K&J magnet calculator) were significantly greater than 2 kG.

    There were major differences in transfer function between a coil that was loaded the ferrite slugs and the same coil with conventional steel slugs. (Tried to post a JPEG of the spectrum analyzer trace but got a message saying I didn't have permission to do so - send me an email if you would like a copy of the PDF version). The ferrite slugs significantly increased the height of the resonance peak and putting a fully magnetized alnico 5 bar in contact with the slugs (in the same way as it would be mounted in a HB) dropped the peak by about 50%. Mounting the same magnet the ends of the slugs dropped the peak to about 25% of its original value.

    A set of pickups with the same ferrite slugs sounded good. The bridge had 5500 turn machine wound coils, an alnico 2 magnet and 1010 screws. The neck had 5000 turn coils, an alnico 4 magnet and 1010 screws. I put them in a old Epi LP Classic that I often use for testing and I was pleasantly surprised with the tones that I got from my Carr Skylark. They sounded very clear but the Alnico bars and steel screws had enough loss to keep them from being sterile. I expected the bridge to be harsh and ice-picky but found that the top end was well behaved. Overall I liked the tone better than the the Classic 57's that I took out of the guitar to test the ferrites.

    It will be interesting to see what I can do to the tone with field modifiers and pole caps - the low core loss of the ferrites should make the slug coil a good 'blank canvas' for tone mods.

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    Junior Member Tone Cam's Avatar
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    Spectrum analyzer trace for previous post

    Analyzer output 072818.pdf

    I think that I figured out how to upload the analyzer trace.

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    Thanks for catching a mistake in my statements, I corrected my post above so that it's not too confusing now

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    Let's see the effects of a magnet proximity to the coil:
    1. no magnet
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    2. Humbucker type ceramic magnet at one side of the coil results in virtually no inductance drop
    Click image for larger version. 

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    3. However with two stronger single coil type arrangement ceramic magnets it looks quite a bit down
    Attachment 49903
    I hope to measure the B of the magnets tomorrow, but my measurement range is 130mT only (approx)

    Meanwhile if we revisit the ferrite pole material specification it looks like it looses quite a bit of initial permeability at fileds as low as 100mT:
    https://www.ferroxcube.com/upload/me...le/MDS/3b1.pdf

    (it is not very obvious to read from the B-H curve provided as you need to look at the B-H curve slope versus B value)

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    Last edited by darkfenriz; 07-29-2018 at 11:19 AM.

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    Meanwhile if we revisit the ferrite pole material specification it looks like it looses quite a bit of initial permeability at fileds as low as 100mT:
    https://www.ferroxcube.com/upload/me...le/MDS/3b1.pdf

    (it is not very obvious to read from the B-H curve provided as you need to look at the B-H curve slope versus B value)
    To be clear, AC µ cannot be read from the B-H curve. It is NOT identical to the slope dB/dH. What you want is a curve like the one called (reversible) Permeability vs. DC Bias shown in this document:
    https://www.mag-inc.com/Media/Magnet...7.pdf?ext=.pdf

    For this special high permeability ferrite, µ drops from the initial value of around 20000 to below 10 at an H-field of 1000A/m, corresponding to only 13Gauss or 1.3mT. But these measurements are taken in a laboratory situation, where the material is placed in a uniform H-field.
    The actual B and H values inside a PU core vary from point to point and are practically impossible to measure. Consequently core sections closer to the magnet may already be in saturation while regions further away don't.

    Of course it makes no sense to use such extremely high µ materials in PU cores. A change from µ=20000 to µ=2000 will barely be noticeable. But a change from µ=200 to µ=20 will.

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    Quote Originally Posted by darkfenriz View Post
    B=µH
    dB/dH=µ
    I must be missing something here, care to explain?
    Sorry, this is really complicated stuff which cannot be explained in a few words. I would refer you to some standard literature on ferromagnetics. You may want to look up "incremental permeability" and "reversible permeability".

    Just so much: Your typical hysteresis or B(H) curve is taken under steady-state conditions and cannot give information for AC fields. Small AC fields superimposed on a DC field produce minor loops. These minor loops have a lesser slope than the major loop/curve. And the slope of the minor loops determines the reversible permeability, which is relevant for the inductance. So you have to take µ=dB/dH from the minor loops, which is typically smaller than the dB/dH of the major loop.

    Actually there are many different permeabilities, as can be seen from the list of section 221-03 of this international standard:
    http://www.electropedia.org/iev/iev....nform&part=221
    Which of them is relevant depends on the specific situation/problem.

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    Quote Originally Posted by Helmholtz View Post
    Sorry, this is really complicated stuff which cannot be explained in a few words. I would refer you to some standard literature on ferromagnetics.
    wow, some great attitude there

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    Helmholtz is right about the 'complicated' part. Chap 3 of the Goldman book talks about AC effects in ferrites but only briefly mentions reversible permeability. He reprinted a figure from Bozorth (https://www.wiley.com/WileyCDA/Wiley...eCd-IEEE2.html) that explains the differences between initial perm (small field variations in unmagnetized material), dc perm (slope of the major hysteresis loop) and reversible perm (dB/dH for DC biased material) and states that reversible perm differs from dc perm due to eddy current effects.

    It seems like reversible perm is the closest match to the slugs in a pickup but I can't figure out if it is appreciably different than DC perm at audio frequencies. I'm guessing that reversible perm (like most other ferrite properties) will depend on the material.

    The fact that I could find a material that didn't saturate at Alnico field levels and sounded good in a set of pickups indicates that ferrites could be a useful alternative to traditional pole materials. Like everything else in a pickup there is enough variation in the properties of available materials that it will take some trial and error experimentation to figure out what compounds sound the best. I've got copies of Goldman, Bozorth and Cullity and Graham (https://www.wiley.com/WileyCDA/Wiley...eCd-IEEE2.html) but believe that I would have to start looking at journal references to come up with a clear idea of whether the published manufacturers data will provide anything more than a qualitative indication of what materials would be useful to try.

    Ferrite compounds are optimized for specific applications and it's probably easier to get samples from a few different classes and see how they sound in a pickup. I am guessing that low perm power cores are not going to sound the same as higher perm materials that are optimized for RF applications.

    The most useful thing that I am taking away from this discussion is a realization that the negative opinions that I have had about ferrites for the past 8 or 9 years were wrong. Darkfenriz' results and the pickups I put together this week indicate that at least some of the ferrite materials sound good when they are used as slugs in conventional HB designs.

    I am really glad that darkfenriz told us about his results with the Ibanez pickups.

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    Glad I could be some help/inspiration.

    My background with ferrites is mainly SMPS-related (conversion/filtering) and more recently operation in mild (and isotropic) DC magnetic bias (nearby MR imaging units) so I believe I have my imagination on hysteresis and magnetization, but I probably look at things from a different perspective and a different feeling on what does and doesn't matter.

    Out of curiosity - what ferrite materials did you try?
    My initial try has been ferroxcube 3B1
    https://www.ferroxcube.com/upload/me...le/MDS/3b1.pdf
    for moderate permeability and good availability, but I agree the results could be different with power compounds like 3C90...

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