It's an interesting idea, but I think you'll find that trying to make an E-core that will fit into that small a space will be terrifically challenging, if not altogether impossible.

I think, not necessarily ferrite, some soft magnetic alloy of about 1/16" thick will do. For the experiments it's OK to make it manually, with pliers. Besides, I feel the U must be oriented along the strings, not perpendicular, so, we can easily afford extra 1/8" of space.

McSeem

 

You'll need to use the proper material. You might try salvaging some E-cores from junked power transformers, and cut/bend to fit.

 

I was thinking along the lines of a single, common U channel across (under) the strings, with the six individual magnets & coils sitting in it.

 

I would start by trying to duplicate the same basic configuration that a typical pickup would use, as it is a tried and true design. Get that part working well first.

Then try experimenting with different things, changing only one thing at a time. You will then be able to find out much more quickly what works, and what does not work.

 

I was thinking along the lines of a single, common U channel across (under) the strings, with the six individual magnets & coils sitting in it.

I'm not sure it can significantly change the configuration, but I'll give it a try if I find some suitable alloy.

I would start by trying to duplicate the same basic configuration that a typical pickup would use, as it is a tried and true design. Get that part working well first.

Yes, I know, for now it's only very very beginning. But it's exciting.

Another potential problem is that the very same magnet pulls the low strings strongly, while the high strings are thin and are attracted weakly. So, what could be the best way to equalize the fields, assuming that I don't have a possibility to order custom magnets with different surface gauss?

 

I'd try to optimize it for the two strings in the middle. Then you can "tweak" the preamp for the low and high strings.

 

How about stacking small neodymium disc magnets?

I've seen these down to the size of tiny watch batteries on ebay, you could stack different numbers with small steel washers as packing to equalise the lengths of the overall stacks but with different field strengths.

I just did an ebay search for 'neodymium'; the second result in the list was discs of 4mm dia by 1mm thick - they sound about the right size!

 

How about stacking small neodymium disc magnets?
I've seen these down to the size of tiny watch batteries on ebay, you could stack different numbers with small steel washers as packing to equalise the lengths of the overall stacks but with different field strengths.
I just did an ebay search for 'neodymium'; the second result in the list was discs of 4mm dia by 1mm thick - they sound about the right size!

Thanks, that's a good idea, although, it will require using bobbins, which will reduce winding space. I planned to glue small plastic washes and wind directly. Elmers ultimate high performance glue does the job perfectly.

The best place to order magnets is K&J Magnetics
http://www.kjmagnetics.com/

 

Another thing to consider is permeability. The higher permeability is the more inductance increases, compared with an air coil. But I have a suspicion that neodymium magnets have low permeability compared to regular iron or soft magnetic alloys. They are highly coercive, but don't significantly increase the inductance. Can you tell me, is it right or wrong? In other words, if I use a neodymium magnet core and an iron core in the very same coil, what would be the difference? The presence of permanent field does not affect the inductance. Permeability does.

So, I don't have an LC meter, can I ask somebody to help me check it? You just take an air coil and compare the inductance with a neodymium magnet and a piece of nail of the same size. Thank you in advance!