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Building a Magnetic PUP, Any help on design????

Brand new to this ball of wax after my wife got me a ukulele and I decided to build a DIY amp (runoffgroove little gem). It didn't work well with the uke but did with my old Peavy guitar so I started looking into different ways to fix the impedance mismatch and then suddenly I'm building a canjo for my youngest daughter....

I digress but anyways I want to build a magnetic pickup out of a wall wart and have found a nice 12 volt model. I watched the video from the fella who started building these and have some questions about pickup design. I've scraped as much as I can from google but still have questions. Namely....

1. If you build a pup with a magnet under neath the coil and then put poles on top does it matter which way the magnet is polarized? I.e. can it be polarized horizontally? I think it can if I remember my electromanetics 101 but cant remember hot to visualize which way creates the most inductance/power.

2. If you use poles on top of that magnet rather than placing it inside the coils do the poles have to be in contact with the magnet? I think the answer is no because it's the field that is being impacted by the poles so there is no need to be touching the magnet.

3. What does the distance between the coils and the poles and/or magnet do to the performance of the pickup? Specifically, does a single really thick bar type pole that goes across all of the strings need to be close to the wall-wart coil or can there be quite a bit of white space in there without hurting performance too much?

I know many of these are noob questions and I should be able to get out my old books and pencil out some of the key bits but I'd like to seek the voice of experience first. Many thanks....

Billy

Tags: coil, magnetic, pickup, poles, wall-wart

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Permalink Reply by Skeesix on June 5, 2012 at 1:45pm

A pickup is a coil wrapped around a magnet (or around a iron/steel pole piece which is in contact with a magnet). If the magnet is a short distance from the coil, it may still work, but be very weak. Of course, if it's too far from the coil, it won't work at all. You can experiment to see what happens.

Magnets and/or pole pieces are oriented either North Up or South Up. You can experiment and see what happens if you orient it the other way. It may still work, but not as well. Just a guess as I haven't tried it myself.

If you're removing the metal leaves from inside the transformer coil with a razor knife, be very careful not to hurt yourself. In my opinion, this is an accident waiting to happen, and I don't recommend doing it.

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Permalink Reply by The Phrygian Kid on June 5, 2012 at 3:00pm

An essential tool for making pups (besides a multimeter and soldering iron) is a pair o alligator clips soldered onto a cable with a quarter inch jack or plug at the thee end. You need this to test your pickups in an amp. Given that you need to make this anyway why not experiment and answer your own questions? Get hookup wire on each end of te coil, clip to cable, hold up to an existing guitar and try various magnet strengths in various deployments...
Good luck.
Ps the videos you saw are not from the guy who started making these, it's a very old trick. There are useful coils in all kindsa stuff too not just wall warts.

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 3:04pm

I have experimented a lil with pickups and I used a wood top and bottom with holes drilled the size of the steel pole peaces I cut from metal rod from the local hardware store. Here is a few pics of what I have.

I super glued the pole peaces to the wood top and bottom and wrapped electrical tape around the metal rods to form a bobbin.

Hope it helps I will exsplane more as U ask or what!

Attachments:

DSCN4283.JPG, 2.2 MB

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Permalink Reply by The Phrygian Kid on June 5, 2012 at 3:07pm

And I agree 100% with skeesix about removing those layers of steel. Pain in the butt an I pretty much guarantee you'll get blood on it if you try. Try to attach your magnets to it and charge it to be part of the magnetic field

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 3:11pm

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 3:13pm

This is a top view

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 3:16pm

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 3:16pm

a view to see the coil

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Permalink Reply by The Phrygian Kid on June 5, 2012 at 3:22pm

great effort there, not at all unlike Ted's awesome stonehenge pickups, except he uses alnico rods for pole pieces ala fender, whereas I assume you stuck magnets to the bottom of the poles.. Congratulations its an awesome feeling when the first few work out huh.. (ps try nails!.. see my pics)

the original poster wants to repurpose existing coils rather than get into winding..

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 5:31pm

Yes , I want to make some using the alnico rods but just have not got around to buying some yet.

I try to use as much free stuff as I can find, kinda recycle out of scrap bins and such.

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Permalink Reply by Jimbo Cawthron on June 5, 2012 at 3:21pm

Then I purchased some lil round magnets from hobby lobby They are real strong, I doubled them one on top of the other and put them on the bottom of each pole peace. here is a pic for that.

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Permalink Reply by Billy Jackson on June 5, 2012 at 11:49pm

Thanks All! I will keep y'all posted as I go.

@Skeesix, do you know a better way to do it because I was pretty stumped by those blades once I opened the case on the darn wart. Good grief what a mess...

@Tea Belly, I hadn't seen the Galileo link and that one helped a bit. Will study that design a touch as I go.

@Phyrgian, I'm going to give that a wack and see if I can get some measurable results with a few different configurations/magnets/poles/whatever....

@Jimbo, thanks for the great piccs! Love that design. Did you notice any difference once you added the extra magnets under-neath???

Appreciate all the help!

Billy