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Thread: How to delaminate a transformer core for pickup blades?

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    Senior Member Stealth's Avatar
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    How to delaminate a transformer core for pickup blades?

    Thanks to a friend of mine who keeps a lot of stuff around, I got my hands on two rather sizable transformer cores (the E-I variety), both made from laminated silicon steel, one from 0.4mm laminates, the other from 0.8mm laminates. Since silicon steel has already been recommended here as good magnetic material for pickup blades, I thought I'd give it a try.

    Machining the blade won't be a problem - I've enough basic metalworking experience to cut it to proper length (enough to cover a jazz bass pickup's length, for instance), but I'm unsure how to actually de-laminate it. The trouble is the entire core is apparently lacquer-potted and, while my friend warned me I could probably split the laminates mechanically, I would probably break off several laminates and damage them badly (maybe salvage them for a shorter pickups such as half of a Precision splitcoil). Is there any way to dissolve the lacquer potting and preserve as much metal as possible without damaging the metal as well?

    Also (and I can only hope one of the blade gurus will chime in ), would using thinner or thicker blades work well? Would there be any harm in (re)gluing two 0.4mm blades and using that? Or would 0.4mm blades work as well?

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    Pickup prototype checklist: [x] FR4 [x] Cu AWG 42 [x] Neo magnets [x] Willpower [ ] Time - Winding suspended due to exams.

    Quote Originally Posted by David Schwab
    Then you have neos... which is a fuzzy bunny wrapped in barbed wire.

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    get an empty large metal paint can with lid and dunk them in that and cover with acid type paint stripper or acetone, shove the lid on and leave it to do the job. No the stripper won't eat the metal.

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    Quote Originally Posted by jonson View Post
    get an empty large metal paint can with lid and dunk them in that and cover with acid type paint stripper or acetone, shove the lid on and leave it to do the job. No the stripper won't eat the metal.
    Acid type strippers will eat the metal. Alkaline strippers may also cause trouble.

    It's best to use only solvent type strippers. Soaking in MEK (Methyl Ethyl Ketone) or acetone overnight should work. Failing that, look for paint strippers containing methylene chloride plus methyl alcohol (methanol), such as "5F5".

    You will need to insulate the freed laminations from one another when making the blade-pickup blades. A new coat of varnish should work. Or sheets of very thin mylar or epoxy-saturated paper. The voltage is very low, so almost anything non-metallic will work. Mechanically strong insulators that glue easily will be the least trouble.

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    Noodle of Reality Steve Conner's Avatar
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    The laminations are already insulated from each other by a thin film of oxide, rust and/or varnish in the original core. Otherwise the transformer wouldn't work. If you don't damage the film, you can reuse them.

    I'd just split off a wad of the the required thickness from the "I" by prying it up with a knife (or a hammer and bolster chisel if it's too stubborn!) and then cut it down to length with a hacksaw, clamping the wad you want to keep in a vice so it doesn't delaminate.

    Heating in a low oven can soften the varnish and make this easier.

    It seems to me that if you want to go to the trouble of making laminated blades in the first place, then the thinner the laminations the better.

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    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Senior Member Stealth's Avatar
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    My idea is to attempt with any kind of blade, laminated or not. As I haven't ever taken a measuring caliper to a bladed pickup, I haven't a clue as to what thickness the blades actually are.

    If memory serves (from re-reading the MEF archive on my hard-drive), the good thing about laminated blades would be minimizing eddy currents, thus lessening the loss of high end. What I've got on my hands for now will serve the need for a basic wind, at least.

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    Pickup prototype checklist: [x] FR4 [x] Cu AWG 42 [x] Neo magnets [x] Willpower [ ] Time - Winding suspended due to exams.

    Quote Originally Posted by David Schwab
    Then you have neos... which is a fuzzy bunny wrapped in barbed wire.

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    Sorry to stray off a little.

    So I'm gathering here that these laminations are just thin strips of ferrous material electrically insulated from one another yet bonded together in close proximity - what do they typically use for the 'insulating barrier?

    Would it be possible to make suitable blade type laminate material by say varnishing thin strips of steel (ie like those used to blank off unused PCI slots), then supergluing them together (if so, that might be easier than hacking away at a larger transformer core - or at least making access to laminations more accessible!).

    Also, where the DIY laminated blade 'mates' with the pickup magnet, should the laminate insulation be scraped off ...or should that remain?

    PS Stealth if you look at the blade type bobbins on sanhemusic's website - the width of the slot is typically, 1.6mm, 3.2mm or 5mm (dunno what that is in old money - I gave up 'base 64' type measuring systems when I was 6yrs old )

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    Noodle of Reality Steve Conner's Avatar
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    Quote Originally Posted by peskywinnets View Post
    Would it be possible to make suitable blade type laminate material by say varnishing thin strips of steel (ie like those used to blank off unused PCI slots), then supergluing them together (if so, that might be easier than hacking away at a larger transformer core - or at least making access to laminations more accessible!).
    Sure, except that junk steel won't be as good magnetically as the stuff a transformer core is made out of. That's the whole point of salvaging a transformer core, the quality of the metal. The fact that it comes in thin strips is just a convenient bonus.

    Those bobbins sound perfect for jamming 0.4 or 0.8mm laminations into.

    Some speaker crossover inductors have a laminated iron bar in the middle that could be salvaged for experiments.

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    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Quote Originally Posted by Steve Conner View Post
    Sure, except that junk steel won't be as good magnetically as the stuff a transformer core is made out of. That's the whole point of salvaging a transformer core, the quality of the metal.
    I agree with that...but junk steel isn't likely to have that much carbon added into it (vs say stainless, or bright steel)...last I tried, they were *very* magnetic. (meaning an unscientific assumption of high ferrous content!)

    I was more thinking that not everyone has access to quality transformers to cut the laminations up & might want to dabble making their own blade material ...I'm no expert hence the line of questioning - just trying to open up an area of exploration.

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    Noodle of Reality Steve Conner's Avatar
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    The pickup experts might disagree, but the whole point of transformer iron is that it DOESN'T retain much magnetism. It can carry a lot of flux before saturating, but it doesn't hang onto it once the MMF is gone: it's magnetically "soft". That reduces hysteresis losses, so a transformer made of it will run cool and transfer signals efficiently with low distortion.

    And it seems to me that this same low hysteresis would do something good to the tone of your pickup. After all, the magnet is the "hard" part of the magnetic circuit that retains the magnetism, and the pole pieces are just there to guide it towards the strings, and guide the little wiggles in the field made by vibrating strings back onto the coils.

    But maybe one of the pickup guys knows why soft iron would be a bad thing.

    You can pick up transformers off the kerb any day of the week, try an old stereo or microwave oven. (but discharge those capacitors first folks!) Nowadays they should all be made of grain-oriented silicon steel.

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    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Senior Member Stealth's Avatar
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    Quote Originally Posted by peskywinnets View Post
    Sorry to stray off a little.
    Also, where the DIY laminated blade 'mates' with the pickup magnet, should the laminate insulation be scraped off ...or should that remain?
    I don't think it'd affect the pickup's tone much, in case the laminate insulation is very, very thin (it's been a while since my EE classes, so I don't recall what the falloff is, maybe distance to the third)? No harm will come from lightly scraping it off anyway.

    Quote Originally Posted by peskywinnets View Post
    PS Stealth if you look at the blade type bobbins on sanhemusic's website - the width of the slot is typically, 1.6mm, 3.2mm or 5mm (dunno what that is in old money - I gave up 'base 64' type measuring systems when I was 6yrs old )
    Thank you - that's exactly the info I needed. 1.6mm would equal either 2 thick or 4 thin laminates so I'm good to go. Also, no need to go "old money" - I'm surrounded by metrics every day here.

    Quote Originally Posted by Steve Conner View Post
    The pickup experts might disagree, but the whole point of transformer iron is that it DOESN'T retain much magnetism. It can carry a lot of flux before saturating, but it doesn't hang onto it once the MMF is gone: it's magnetically "soft". That reduces hysteresis losses, so a transformer made of it will run cool and transfer signals efficiently with low distortion.
    That's the same basic conclusion I reached - if I have a hard magnet (in my case an NIB35 block) underneath the pickup providing the magnetic field, the silicon iron core I got should provide for a solid enough core.

    Can the grain orientation (or, rather, anisotropy vs. isotropy) somehow be detected? How much will it affect the sound of the pickup, if any?

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    Last edited by Stealth; 03-04-2010 at 05:17 PM.
    Pickup prototype checklist: [x] FR4 [x] Cu AWG 42 [x] Neo magnets [x] Willpower [ ] Time - Winding suspended due to exams.

    Quote Originally Posted by David Schwab
    Then you have neos... which is a fuzzy bunny wrapped in barbed wire.

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    Greetings,

    Once you have the bare assembly on the bench, the first "I" plate can be pry'ed off fairly easily. Using a thin flat-bladed screwdriver, gently tap out the mating "E" plate. It will be a little tight. After a few plates are out, things come apart easier.

    Probably not the best way; I cut lamination to size with tin snips, flatten them with a soft mallet, then superglue the clamped assembly. So far, have not tried additional insulation between lams, just relied on the coating that was on the lam surface already.

    All sorts of blade configuration are possible. My impression supports what someone already pointed out earlier; generally, thin-bladed cores tend to sound brighter, fatter-bladed cores sound warmer. Expect increased inductance of coils with fat-bladed cores. All factors that will play part in the sound.

    FWIW, a few pictures of laminated bladed pups I experimented with.
    1. Single coil size stack with multiple lams.
    2. Single coil size sidewinders with 2-3 lams.
    3. Hybrid Humbucker.
    4. Humbucker-sized sidewinders with blades facing the strings. The neck pup has rods in the coils, the bridge uses two bladed coils.

    Regards.

    JBF.
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    If you look carefully, you can find transformers that aren't potted, many of the ones sold at Radio Shack used to be that way. You can also talk some of the lamination suppliers (like Tempel Steel ) to send you a few samples. If you look carefully, you may even be able to find an I section very close to the size you'd need for a pickup.

    It's been several years, but the last time I asked Tempel nicely they supplied EI samples quite quickly for free.

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    Quote Originally Posted by MKB View Post
    If you look carefully, you can find transformers that aren't potted, many of the ones sold at Radio Shack used to be that way. You can also talk some of the lamination suppliers (like Tempel Steel ) to send you a few samples. If you look carefully, you may even be able to find an I section very close to the size you'd need for a pickup.
    Unfortunately there's no such thing as a Radio Shack (at least not under that name, seeing as I'm not in the US), but I'll check around. This particular core I have (should've taken the picture, I know) is lacquer-potted, so I'm stuck with it for the time being.

    Quote Originally Posted by MKB View Post
    It's been several years, but the last time I asked Tempel nicely they supplied EI samples quite quickly for free.
    Thanks for the hint - I'll contact them.

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    Pickup prototype checklist: [x] FR4 [x] Cu AWG 42 [x] Neo magnets [x] Willpower [ ] Time - Winding suspended due to exams.

    Quote Originally Posted by David Schwab
    Then you have neos... which is a fuzzy bunny wrapped in barbed wire.

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