I have done some research but I still get confused when I see people's pigtail leads coming from opposite sides of mine, and the nomenclature of Reverse Wound vs Reverse Connected.

So anyways this is exactly what I've been doing,:

1. Both Slug and Screw bobbins are wound in the same direction on my machine, the bobbin is on the right side of my machine spinning away from me.

2. I'm using black pigtails for my "starts", and white pigtails for my "finishes"

3. I'm wiring South Start (black screw side) to Ground

4. South Finish (white screw side) to North White Finish (white slug side)

5. North Black Start (black slug side) to Hot

If someone could just let me know if this is correct, I would greatly appreciate it. ]]>

I agree with Helmholtz comments in that other discussion that the the player has little need to know the C of a pickup; it is swamped by cable capacitance and the guitar sound can be varied easily by cable selection. I also agree with Joe Gwinn, who said that the purpose of measuring C is related to pickup design. In particular, I want to rate pickups according eddy current effects as a function of frequency. My method for accomplishing this needs a good measurement of C. I have done this before by making a mathematical model of eddy current loss and including it with the other parameters and fitting everything at once. What I want now is a way of measuring C (not perfectly, but with sufficient accuracy) to reveal the effects of the eddy currents without having to model them. This is possible with higher frequency measurements that reveal more information about C without so much contamination from the inductance.

The first attachment shows the impedance up to a frequency of 80 KHz (based at a sampling rate of 192 KHz) of a humbucker screw coil with very short leads and removed from the base plate. This is a brand X pickup made in Japan some years ago. It is not possible to say much about eddy current effects from looking at this plot, and so there is some way to go to meet the goals of the project!.

Now it is necessary to determine how well the instrument (an Apogee Element 24 and computer) works for measuring capacitance. The second attachment shows the admittance of a test measurement. (Admittance (Y) is the reciprocal of Z, Y = 1/Z. It is a straight line with positive slope for a capacitor. It is good to display Y rather than Z for a capacitor since it is easy to see deviations from a straight line.) The measurement looks good up to a bit beyond 70KHz. The line starts bending down beyond that. The derived C value agrees well with the Extech. This value is determined by fitting a function to the measured data as a function of frequency. The description of this is coming in a later post.

Eddy currents reduce the apparent inductance of the pickup coil, more with with increasing frequency. The imaginary part of Z for an inductor is a straight line with positive slope. When eddy currents are present, their effects increase with frequency and the line bends a bit in the downward direction. We expect the effect to be present in the data displayed in the first attachment, but obscured by the effect of the capacitance. But if we know the capacitance, we can remove its effect on the measured impedance. The pickup is an L in series with an R all in parallel with a C. Admittances add for devices in parallel, also we have Ypm = 1./(j *w*L + R) + j*w*C. We use w for omega = 2*pi*f. Ypm is just 1/Zpm, the measured data. From that we subtract j*w*C, using the measured value of C. This leaves the first term; take its reciprocal to get an impedance, easiest for viewing an inductance, and we get R + j*w*L where both L and R might vary with frequency. If there are no eddy currents the imaginary part of this should be a straight line, and this line should match the line found by taking the low frequency inductance, call it Lcoil, and making j*w*Lcoil. If there are eddy currents, the measured data as a function of frequency should bend downward from j*w*Lcoil.

To begin testing this, we take the screws out of the humbucker coil (to remove the eddy current loss), measure the impedance, and do the calculations described in the previous paragraph. The results are shown in the next attached plot. The good agreement of the dashed and colored line over the entire audio range suggests the the measured value for C is good, that is, as good as we need it to be. (The determination of C used measurements between 20KHz and 40KHz only; use of higher frequencies will be investigated later.)

Repeat the measurements and calculation with the screws installed, and we get the the last attached plot. The measured C is very nearly the same. This probably means (subject to additional verification) that C changes little or not at all when eddy currents are introduced and that the position of the vertical line below the dashed line is a measure of the eddy current effect as a function of frequency.

The next post will describe how C is found from the measured Z, or actually Y.

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i recently watched this video of someone assembling a pickup from junk materials, which got me thinking that maybe i could make my own:

https://hackaday.com/2019/04/14/buil...up-from-scrap/

at the moment, i don't have any neodymium magnets, but i do have some ferrite cores. i am wondering if wrapping a thin gauge magnetic wire around a ferrite core many times would function as a kind of pickup.

after watching a number of videos, it seems that there is a great deal of sensitivity related to the number of winds and the tightness of the winding - but what i don't understand is the relationship between a densely-wound pickup and the output result. is there more hum? better frequency response? a wider magnetic field?

finally, i'm curious about the difference between a guitar pickup and a tape head. it seems like i can play sound through a tape head and a guitar pickup will amplify it, but i can't hear actual tape when i run it across a guitar pickup. what would have to change in a guitar pickup to play back magnetic tape?

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