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The instrument I want seems to be hard to get hold of in my country, so I'm building one. I won't say which instrument, so that the answer will be more generally useful.

I have sourced a magnet that's wide enough to span the width between two strings, and I'll probably use a wire from some cheap headphones (easy to source and usually have a thin layer of insulation). Now, I understand basic digital electronics but I have no intuition as to why a pickup is even going to work. So I don't know which way to arrange the magnet or anything either.

Does North need to face outward or into the body of the instrument? Or even toward either end of the string?

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    I really think that you should tell us the type of instrument and what the strings will be made of. There are pickups that detect string movement for solid-bodied guitars but this requires steel strings. For acoustic instruments and instruments that don't have metal strings, you need a different kind of pickup. Also you don't have to buy the whole instrument to get a pickup. They can be bought separately. Please tell us the instrument with a photo if possible. Nov 23 '20 at 0:35
  • @chasly-supportsMonica Maybe you are right. I'll tell you then. It's the dombra, from central Asia. I've got these steel cello strings I'm planning to use but I'm not married to that idea.
    – OmarL
    Nov 26 '20 at 10:48
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The magnet poles should be in the direction perpendicular to the plane of the strings.

For an individual single coil pickup the polarity of the magnet doesn't matter. If you use several magnets, they all should have the same polarity.

Polarity starts to matter when you combine several single coil pickups. The most common humbucker configuration uses two pickups with opposite polarity and opposite coil connections.

Note that typical guitar pickups have thousands of winds in the coil, so cable from headphones might be too short.

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  • Yeah also it seems the core is merely to alter the electric magnetic permutivity the medium or something. What's important is the coils and increasing the turns would seem to improve the signal i suppose. Nov 22 '20 at 14:33
  • @marshalcraft From my research there appears to be a trade-off with the number of windings. Increasing improves the signal strength, but according to some sources this can lead to a loss in sensitivity. With coil-tapping, an extra set of windings can be switched in/out of the circuit to make adjustments on this axis. Nov 22 '20 at 17:40
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    The more winds, the higher overall sensitivity of the coil, but also the higher inductance of the coil, which leads to dampening of the high frequencies, so one has to find some compromise. Still, length of a headphone cable seems to be far away from what most would call a compromise. Nov 22 '20 at 18:25
  • "it seems the core is merely to alter the electric magnetic permutivity the medium or something" I'm not sure what makes it seem that way to you. Did you ever wonder why magnets are used instead of just steel/iron/ferrite slugs? It's because it's necessary for the strings to be magnetized ("made magnetic"), and they get this property imparted to them by the field from the magnets.
    – Beanluc
    Nov 22 '20 at 21:49
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Others have addressed the magnet orientation, so just to add one additional point.

The cable from headphones will be magnitudes too thick for this task. You will barely get a couple of dozen winds even if your cable is long enough. You need about 1,000 or so. The wind count & layout will vastly affect the resulting pickup. Pickups are wound by machine, even if the machine is hand-powered, because this is not really one of those tasks humans are good at. Imagine taking all the cotton off a sewing bobbin, then putting it all back again, neatly.

You can buy pickup wire, it's actually really cheap - e.g. https://www.wires.co.uk/acatalog/gpw.html - but if you can't stretch to that, then another source would be wound voltage transformers from power supplies. They use the same type of wire.

Pickup (& any transformer winding) is extremely thin copper wire with a microscopic thickness of insulation. Nothing else can be substituted.

I also found this on the differences wire types & winding can make - https://mwswire.com/guitarpickup/

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With single cool pickups, like with Telecasters, if you wind one with reversed windings and reversed polarity, aka RWRP, your serial position will be noise-free, like a humbucker. With Stratocasters, there is no neck-and-bridge option, the middle is made RWRP so the 2 and 4 positions are noiseless.

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    This is a poor answer in my opinion, because the asker gave a minimum degree of specifity, namely the exact 3d orientation of the field/coil. That said, what you are talking about does sound interesting, but to me it is not concrete for what was asked. Let's stop beating around the bush. Nov 22 '20 at 14:27
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I think normally you would use six magnets, one for each string, or you whole use one large magnet in the shape of a plate that spans all six string and have six pole pieces for each string that are ferrous and screw into the big magnet.

Either way the magnetic field should be perpendicular to the body of the guitar, but it doesn’t matter whether north or south is pointing out of the guitar, as long as all the magnets have north in the same direction.

One thing you might want to do before building your first pickup is build a simple battery powered electromagnet and see how that works. A pickup is like six electromagnets combined into one thing except instead of the magnetic field being created by electricity in the coil, the field is created by the magnetic metal and the that sort of makes electricity in the coil.

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The OP has revealed in a comment that the instrument is a dombra.

enter image description here

This is a traditional instrument with two strings, from central Asia.

Traditional strings are gut or nowadays nylon as shown here.

enter image description here

It might seem obvious but I'll point out that these won't work with an electric guitar pickup. For that the strings should be steel.

The sound hole of the dombra is very small and so not suitable for an acoustic-guitar-type pickup.

enter image description here

Traditional solution

If you want to stay traditional then I suggest a surface-mounted Piezo Transducer Pickup as used for violin, ukulele, or cigar-box guitar. These detect the vibration of the soundboard of the instrument. They can be bought online from China and are very cheap.

enter image description here

Steel string solution

If you are not worried about being traditional then you can use steel strings and even a solid body if you wish.

In that case here is what you need to know:

enter image description here

enter image description here


Source of pictures

These pictures and the full text are available at How Does a Guitar Pickup Really Work?.

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