Blades vs. Polepieces- What's the difference?- created 03-12-2006

Mahajan, Rohit - 03/12/2006.07:39:47
Putting things where they're not supposed to be...

Hey

I don't know if it sounds different, but the blade is better for string bending. If you have a polepiece pickup, and the poles are raised above the coils, the volume will drop off when you bend a string.

The sound is "rounder" or "less focused" depending on your point of view, because the pickup only sense the up and down string motion and not side to side motion any more... I'm more aware of this difference with bass pickups though

The only "advantage" to blades IMO is that you don't bend out of field , but then again I don't really see that as an advantage . I kind of like the madness that happens when you bend so deep it crosses magnetic fields

<i>you don't bend out of field</i>

Yep, this is what I was also saying. I have noticed that if the screws are level with the top of my humbuckers, I don't hear the bending problem to any great degree. But on a Strat, or P90s where the pole pieces are raised high above the coil, I hear it. I'm not sure about a P90 with the screws flush.

The reason I use blade polepieces is so that I don't need to worry about using a strange string spacing, which might also be a consideration

I would like to ask about the Carvin 22 series pickups at this point. It would seem that they would still sound like the blade pickups ? they also make an 11 pole single

They sound a bit different because of the difference in the magnetic field. Multiple magnets/poles produce a more complex field, and you have a lot of stuff going on there.

Also round poles pick up the parallel (sideways) and perpendicular (up and down ... to the soundboard plane.. if it were an acoustic guitar) string motion symmetrically, although that's not necessarily a good thing. Acoustic instruments produce more up and down motion. An asymmetrical sensing pattern is better.

I'm not so sure a blade doesn't pick up parallel movement.

A Carvin M-22 pickup sounds just like pole pieces.

So for staying close to the Strat sound the Carvins would be a better choice than the blades? More complex clarity? <BG>.

Just out of curious or just out there. Anyone ever do magnetized strings passing through a coil. The cover would make a nice palm rest.

>Anyone ever do magnetized strings passing through a coil. The cover would make a nice palm rest.

Yeah, Rickenbacker! (well they passed thorough the magnets)

Somebody hit me with a fryin pan I can't stop thinkin of alinco & or ferite strings

How about a nice little neck instead of a pan? I've got two useless ones now...:(

<i> Which would explain why he said the concept of raising the pole-pieces for volume is rubbish- because extending the field would have little effect, except dampening vibrations.</i>

Then why did he put adjustable screws in? When I adjusted the polepieces on my P90s, it certainly made a difference. When I first built the guitar, the pickps were not close to the strings, raising the polepieces changed the volume dramatically. I also got an effect where bending the strings made the volume drop on the neck pickup; the string was moved off of the pole piece. After I raised the pickup closer to the strings and lowered the polepieces, the bending problem was much less pronounced.

Rohit,

Pickups actually work because the string disturbs the magnetic field around the coil. This disturbance creates a current to flow in the coil. While it is true that the strings do become magnetized, usually permanently, this is not how the pickup operates in general. If the pickup relied on magnetized strings, and didn't have permanent magnets of its own, what would happen when you changed strings? Stings do not come magnetized, and in fact only become magnetized over a small area directly over the pickup's magnets.

Yes, you can remove the magnets on a pickup after the strings have become magnetized and you will still hear sound. I've actually done this in the past. But it does NOT sound the same as when you have the magnets in. It's a very weak tone. The strings do not make very good magnets. If this was the case, it would have been done already. Also different magnet, and polepiece materials give you different tones. Having gaps between the magnets and the polepieces sounds different. Different strength magnets sound different.

Now let's tackle another problem with using the strings are magnets. Humbucking pickups operate on the principal that two coils connected out of phase will cancel any signal that enters both coils, when that signal enters the coils with the same phase relationship. This is known as "common mode." Now if this is the case, you may ask why the sound of the strings doesn't get canceled out? Because each coil has an opposite magnetic polarity. So even though the coils are out of phase, each coil also "sees" the string oppositely, because of the magnets, and when the two coils are summed back together, the opposite polarity (phase) string signal is combined in phase. But any interference that was pickup up is still out of phase and cancels out.

Another interesting fact is that for the most part the coils do not sense the strings, but rather sense the disturbance is the magnetic field. Any magnetism the strings might have is small compared to the magnets. So any change the magnetic circuit will indeed effect the sound, and this includes the shapes of the pole pieces, and their distance from the strings. Bill Bartolini got a patent (3,983,778) on his early "Hi-A" (high asymmetry) pickup design, which is partly based on not having round pole pieces, since they sense the parallel and perpendicular string movement equally, which Bill decided sounds less full than mostly hearing the string vibrations perpendicular to the string plane, which is how an acoustic guitar works. He also used trapezoidal shaped poles for this reason.

So yes, blades sound different that poles, etc. The only reason an adjustable pole piece might not seem to make much difference would be if the magnets under the poles were strong enough to saturate the poles, thus bypassing as it were, the poles.

There's so many ways to make a working pickup, and none of them are wrong. :)

Yeah, the whole humbucking thing does sort of invalidate the theory- anyway, I guess that magnets do affect the volume that way, but the major reason that the pole pieces were adjustable was that it was a selling point- he admits it himself, the first prototypes had the poles completely inside- and the the direction was also selected at random...

The problem with blades is that is they are too thick you end up with too much inductance and a lot of eddy currents. A way around this is to use a thin blade, as Lawrence does, and also make a laminated blade. Bartolini used to make laminated core humbuckers. I have since seen someone has a patent on it (which I think is ridiculous since transformers and other coils have used laminated cores for years!).

If you do it the right way they sound fine. Lawrence L-250's and EMG's sound very much like standard single coils with poles.

Laminated? What are the layers made of

laminated steel

I haven't seen laminated cores yet- a thin one just might work perfectly. Can anyone find a picture of a laminated core? A very small aperture would result in a very clean, distinct sound...would sound good...

Bartolini made laminated core humbuckers for guitar, they had exposed coils... and they very well might use laminated cores in their bass pickups too. EMG uses laminated steel in their CS soap bars.

This is a very blurry picture of the Barts.

#14 "Pickups actually work because the string disturbs the magnetic field around the coil."

It is just as correct to say the above sentence as it is to say "the strings become temporarily magnetized when the pickup magnet is present". The two views are both just approximate ways of understanding what happens. A magnetic field always can be thought of as resulting from the sum total of all the sources that cause it. Saying that the motion of the temporarily magetized string segment induces a voltage in the coil with a ferromanetic core is the same as saying that a disturbance in the total magnetic flux passing through the core caused the voltage. You get to choose!

I think the easiest way to understand the humbucker pickup is to view the string segments as oppositely magneticly polarized, so they induce an opopsite polarity signal in the coils which are electrically out of phase to add rather than subtract the signals. But that is not the only way to view it.

Yes, the strings become magnetized. But they don't make very good magnets. Some types of strings work better than others.

I discovered many years ago that you don't need the magnets once the strings have been magnetized while experimenting with coils. Try removing the magnets from a pickup and listen to the results. I don't think you will like it! Sounds like a very weak magnet. :)