cutting posts?

[Robmosis]

Hello I have been reading that some people cut the post screws level with the bottom of the pickups. What effect does this have on the pickup? And why would it be done?

[David Schwab]

I find you get a stronger signal from the screw coil because the magnetic field is not exiting out the back of the pickup as much.

[Mike Sulzer]

I find you get a stronger signal from the screw coil because the magnetic field is not exiting out the back of the pickup as much.

Magnetic field lines are closed loops. The magnetic field lines from the vibrating string pass through the coil. They have to return to the string. The screw is made from magnetic material and thus tends to stop the lines from diverging out the side of the coil before passing all the way through. (This reduces the output.) The screws do this better when they extend out the back. It is not a big difference, but it is better not to cut them off.

Also the best humbucking effect is obtained when the effect of the cores and screws match. The screws are thinner, but longer.

[Peter Naglitsch]

I know that I’m quoting you a bit out of context, but:

it is better not to cut them off.

gets me going. Better? As in “there is only one way to things”? Or better in what aspect?

Also the best humbucking effect is obtained when the effect of the cores and screws match. The screws are thinner, but longer.

Do you mean that one should stay away from cutting the screws if one want the best hum canceling? If Dave is right (I have not tried cutting the screws yet) and the output of the screw side coil is increased by cutting the screws, your statement is totally wrong. Normally the slug side have a tad stronger output and thus (if cutting the screws increase output and the coils are identical) hum canceling is improved by cutting the screws.

[Mike Sulzer]

I know that I’m quoting you a bit out of context, but:

gets me going. Better? As in “there is only one way to things”? Or better in what aspect?

I wrote that keeping the screws long gives a bit more output; that is what I am referring to as better. Maybe you need to calm down. I did not say anything that should get you going.

Do you mean that one should stay away from cutting the screws if one want the best hum canceling? If Dave is right (I have not tried cutting the screws yet) and the output of the screw side coil is increased by cutting the screws, your statement is totally wrong. Normally the slug side have a tad stronger output and thus (if cutting the screws increase output and the coils are identical) hum canceling is improved by cutting the screws.

I realize that I am saying the opposite of what David said. As I explained, cutting the screws off does not stop the magnetic field from getting out. The field lines must return and make complete loops. His explanation for his observation is wrong.

I do not see how you can say the slug side is a tad stronger. The screws are adjustable; stronger with the screws all the way down? I could believe that, but I really have not compared.

Actually, the output of the screw coil from a vibrating string and its sensitivity to hum are not quite the same thing. You can adjust the screw and change the output level from the string more than the hum because the string is close and the hum source is farther away.

The amount of magnetic material and its geometry affects the sensitivity to magnetic fields. The slug and screws should in principle be matched. I do not think a small mismatch is a big effect. Maybe like using a somewhat different number of turns on the coils.

[David Schwab]

I wrote that keeping the screws long gives a bit more output; that is what I am referring to as better.

No, actually cutting them off gives more output, and you get more pull from the screws also.

Try it and see. Seth Lover said the same thing a few times.

You still get a closed loop cutting them off, but the loop is mostly on the top of the pickup, and not around the back.

[Mike Sulzer]

No, actually cutting them off gives more output, and you get more pull from the screws also.

Try it and see. Seth Lover said the same thing a few times.

OK, I will try it when I get a chance.

You still get a closed loop cutting them off, but the loop is mostly on the top of the pickup, and not around the back.

The field I am referring to is the one from the vibrating string. The lines come down through the coil and then circle back around to the string. The screw helps keep them straight through the core. Those that diverge outside the coil before getting to the bottom do not contribut output to the lower windings.

I think you are describing the permanent field. I am not sure how it is affected.

[David Schwab]

Right. Think about where the magnet is and how the field would loop. With the poles flush with the magnet, you have a nice efficient U. We are talking about a humbucker here, not a single coil with rod magnets.

With the poles poking out behind the magnet, you have another loop from the back of the poles to the magnet. That seems to weaken the pull at the front, which would make sense.

It's one reason the slug coil is louder.

[Peter Naglitsch]

I do not see how you can say the slug side is a tad stronger. The screws are adjustable; stronger with the screws all the way down? I could believe that, but I really have not compared.

Measure the field strength @ the screws and @ the slugs. But before that, please use your ears: Take a standard bucker, four conductor, and listen to the two coils separately. It’s that easy.

Theories are good but first hand experience is better...

[Mike Sulzer]

Measure the field strength @ the screws and @ the slugs. But before that, please use your ears: Take a standard bucker, four conductor, and listen to the two coils separately. It’s that easy.

Theories are good but first hand experience is better...

Measurements and theory work together. If by "theories", you mean BS, please examine your own methods.

I do not have a gauss meter, but there are ways of determining if fields are similar in strength. In this case, we want the field close to the pole pieces. The least formal way is to attempt to pick up the pickup with a piece of steel touching a pole piece or screw at one end of the pickup. The angle achieved before the pickup drops is a measure of the strength. The screw side is slightly stronger in this test.

A slightly more formal way is to use a mini-hacksaw blade (with a small piece of steel attached) as a deflection spring. One measures the deflection with a ruler. The pole and screw are close in this test, with the screw probably slightly stronger.

Now let us use an additional measurement and some theory to help explain these results. If one repeats the measurement on the back side using one of the projecting screws, one finds that the field is significantly weaker there than on the head. The head influences the field strength close in.

One also needs to understand the effect of the spacer bar through which the screws pass. It is in good contact with the magnet and surrounds the screws. The slugs, although thicker, are not so well-coupled to the magnet. This helps explain the observed balance.

I will listen tonight if there is time.

[Peter Naglitsch]

Measurements and theory work together. If by "theories", you mean BS, please examine your own methods.

Man, what’s your problem? I say that theories are good but experience are better. Where did you get that BS part from?

My experience and empirical testing says something completely different than your theories. And when the things I say don’t fit your theories, you claim that I’m calling your posts BS! That isn’t very constructive my friend.

I have already mentioned my methods. Read my posts. And I continuously examine my methods. I upgrade them and expand them. At the moment I use a combination of measuring DC resistance (have no AC resistance meter available), capacity, inductance and field strength of every pickup I make. On top of that I use a signal generator in combination with an air coil to induce a 16 to 24 000 Hz signal into the pickup and measure the frequency response. I even save the frequency response curve from every pickup I make. On top of that I also use my most valuable measurement instruments: My ears.

That is my methods. Do they need to be examined? If you think so, please do that. I am always willing to rethink the way I work. How does my methods compare to yours? What is the most scientific approach? Using a hack saw blade or the above mentioned?

I do not have a gauss meter

As you do not have one, and think that your methods are good enough, I will share my measurements with you. In all of the pickups I have done, the average difference in field strength between the screw and slug bobbin is between 15 and 20% (17.3%). And yes, it is the slug side that is stronger. That my friend is a result that I think one can call conclusive. And that is what I mean when I say that theories is good, but first hand experience is better

BTW, I have not bothered to measure the field strength of the back of the pickup as there is seldom any string vibrations to pick up at the back side of the pickup. And I’m only interested in that; picking up string vibrations.

[SteikBacon]

Peter, when you use aircoil and 16Hz - 20kHz, have you tried to change magnets. I wonder if the different magnets will affect the result you measure. I would think you not get too different results when using different magnets in your test.

I tried cutting screws on my pickups, little difference in the higher frequencies. But my coils are quite unbalanced. Think there will be more affect if the coils are balanced.

[Peter Naglitsch]

Steikbacon, I'm not sure I understand your question 100%. I use an air coil as part of my measuring equipment, not in the pickups. No magnets in or around the air coil at all. But if you mean: have I tried to exchange magnets in a finished pickup that I have already made measurements on and then re-done the tests with the spectrum analyzer to compare the curves, the answer is no. I have tried swapping magnets while listening to the differences. But I do that until i find the tone I'm after and then I measure and plot the curve.

[SteikBacon]

Steikbacon, I'm not sure I understand your question 100%. I use an air coil as part of my measuring equipment, not in the pickups. No magnets in or around the air coil at all. But if you mean: have I tried to exchange magnets in a finished pickup that I have already made measurements on and then re-done the tests with the spectrum analyzer to compare the curves, the answer is no. I have tried swapping magnets while listening to the differences. But I do that until i find the tone I'm after and then I measure and plot the curve.

It´s this I wondered about. Because the pickups sound so different with different magnets I´m not sure if I want to trust curves from tests like those you do. I have an understanding that you measure the coil(s) more than the entire pickup.. But the tests give results about the coils. Just what I´m thinking. I don´t know. There is not so many ways to measure pickups...

[Mike Sulzer]

Peter,

Thank you for sharing your field strength measurements. 17% is not a large number, and I do not consider it in disagreement with my crude measurements, and did not mean to imply that they were particularly accurate or final. I have ordered a calibrated Hall effect chip (and a spare) to make a probe that will allow measuring the field at the string location.

By the way, do you measure at the string location? Are the slugs and screws the same distance from the string?

I do not see anything in this discussion where my "theories" differ from your measurements in any significant way. What am I missing?

Yes, 17% is not very much. It amounts to somewhat more than a db, and a db is about the least difference one could expect to hear, especially given the problems of exciting a string in a repeatable way. The two coils in the humbucker I am testing sound about the same. And they measure about the same using a string as a signal source. One might have a db more, I am not sure. When David has referred to the different sensitivities of the two coils, it seemed he meant more than that.

Is your air core coil (for measuring response) small enough to measure the response near individual pole pieces, or does it look at the overall response?

When measuring the inductance of low Q coils, the dissipation factor (or ac resistance) needs to be measured as well for the results to be accurate. Meters such as the Extech display both. How do you measure the inductance?