need schematic for hum cancelling jazz bass pickups

[David Schwab]

There is a proper scientific reason for that. Inductance goes up as the square of the number of turns, but only if the turns are magnetically coupled together. In other words, if they're all on the same coil. For independent coils the relation is linear: take 5 coils the same and hook them in series, and the inductance will be 5 times the value for a single coil, not 25.

So, if you take a bazillion feet of wire and make one big coil, it'll have more inductance than if you made several small ones from the same length of wire. And, more inductance means a darker tone.

Well Steve, that's the answer right there. Ian Waller from Electric Wood (Wal basses), who designed the pickup and preamp had an electronics background. I'm sure he used multiple small coils for this very reason, as did Bill Bartolini.

I guess some of the pickup physicists might quibble with this. Air cored coils don't quite obey the square law, because the coupling between turns isn't perfect even if they're all on the same coil. And, there will always be some coupling between multiple coils when they're mounted side by side in a pickup.

But I think the argument is still qualitatively valid.

We are not talking about air coils either. All the coils in question have steel cores.

So I'll stick with my comment that multiple small coils are clearer sounding than one or two large coils.

Also, the later Wal pickups had each string's pair of coils in series, and then all the pairs in parallel. But still, listening to the pickup I have hear, as well as the prototypes I have made so far, and Marco's pickups, it's clear that these pickups do not sound like a humbucker with two coils, so matter how you wind it.

Mike, you made single string pickups. What what your reasoning for doing so?

[Mike Sulzer]

Well Steve, that's the answer right there. Ian Waller from Electric Wood (Wal basses), who designed the pickup and preamp had an electronics background. I'm sure he used multiple small coils for this very reason, as did Bill Bartolini.

Here is the statement from the Bartolini patent that you quoted above:

Since both the inductance and capacitance of a sensing coil vary linearly with its mean radius, replacing one coil by multiple small coils can reduce the impedance of the pickup system by a factor equal to the number of coils and raise the self-resonant frequency by a factor equal to the square root of the number of coils.

Notice that Bartolini is implying that the sum of the inductances of the smaller coils is equal to the original since the inductance varies with the linear dimension. I showed a simple case of this in the foot note in my response to Steve. This is not simple stuff, in general, and the shape of the larger coil is a complicating factor..

So who do you believe, Bartolini or Steve? You cannot have it both ways, since they are saying different things. As I wrote above, I agree with Bartolini on this, at least approximately. And as I told you above, your statements about clarity are not consistent with your belief that Bartolini is correct.

Also, I do not know for sure if the situation you are describing is passive, with the pickup connected to a cable, or active, using a preamp with possible loading of the pickup with a capacitor or another impedance. The latter case is complicated, and you would need to know the details in order to predict the sound. It matters how this is donw.

I repeat: this is not simple stuff, and it needs some careful thought.

[Marko Ursin]

To me it's simple; multicoil sounds different from single or dual coils. That's what counts when making pickups for use. Iheory may be different but I guess very few bass or guitar players play their instrument in theory.
Marko

[Steve Conner]

Bartolini says that a system of multiple coils has a higher self-resonant frequency than one big coil. So, I think I arrived at the right conclusion, just by completely faulty reasoning.

Lots of people play musical instruments in theory. Mozart said he could hear the whole concerto in his head before he started writing it down.

[Marko Ursin]

Lots of people play musical instruments in theory. Mozart said he could hear the whole concerto in his head before he started writing it down.

Sure but hey come on, I'm talking abous us bass players

[Mike Sulzer]

He meant using them individually as David said. When you put them back in series, you the get nearly the same inductance as the original coil..

Bartolini says that a system of multiple coils has a higher self-resonant frequency than one big coil. So, I think I arrived at the right conclusion, just by completely faulty reasoning.

Lots of people play musical instruments in theory. Mozart said he could hear the whole concerto in his head before he started writing it down.

[Steve Conner]

So, would it be fairer to say that multiple coil pickups sound clearer simply because nobody wires all the coils in series?

[Mike Sulzer]

So, would it be fairer to say that multiple coil pickups sound clearer simply because nobody wires all the coils in series?

That would do it!

But people do connect them in series. I think the issue here might be preamps and how the pickup is loaded at the input of the preamp. Also there is the issue of connecting them out of phase and the result of the opposite sign of the coupling.

I will have a simple proof concerning the equivalence of coils in series and one big coil later today.

[Mike Sulzer]

Here is a way to see that five square coils (single turn) in series arranged together in a pickup shaped rectangle have the same inductance as a single coil having the same rectangular shape.

We need to know that:
1. Magnetic fields are caused by currents.
2. The total magnetic field can be found by adding up the fields from short lengths of wires.
3. The magnetic field is a signed quantity, and therefore the field from two sections of wire right next to each other with currents in the opposite directions is very close to zero.
4. Inductance is the result of the change in time of a magnetic field passing through a loop or loops of wire.

A sketh:


Follow the arrows indicating the direction of current to verify that the five coils are in series. Remove the sections made up of wires with opposite currents. Connect up the gaps to make a single loop of current around the periphery. See that this single loop has nearly the same effective current as the five loops in series, and so the magnetic field is the same. Changes in time are also the same, and so the inductance is the same, or nearly so.

You can now stack sets on top of each other and perform the same process for multi-turn coils.

[David Schwab]

So, would it be fairer to say that multiple coil pickups sound clearer simply because nobody wires all the coils in series?

Nope. They are wired in series. And as I said multiple times, when I wired up all the coils on the Wal pickup in series (20k) it didn't sound anything like a two coil humbucker wound to 20k.

I think before any more speculation on what its inductance is, or isn't, goes on, some actual measurements should be done. I'd do it, but I don't own an inductance meter.

Judge for yourself:

http://www.sgd-lutherie.com/media/wal_test_series.mp3

The pickup was rigged up on one of my 5 string basses. It's a very tall pickup, so it was hitting the strings a little, and of course only covered 4 strings.

Here's the same pickup with the two rows in parallel

http://www.sgd-lutherie.com/media/wal_test_parallel.mp3

This was plugged direct into the board with no EQ. The mixer has a 10K impedance on the guitar input.

[Steve Conner]

Plugging a 20k pickup into a 10k line input is hardly going to give a fair impression of its tone.

I think Mike's argument fails for round coils. If you imagine the diagram with circles instead of squares, the total area of the 5 small circles is less than the area of the big oblong thing that contains them, and the line segments don't cancel each other out any more, because they're not close together over their whole lengths.

[Mike Sulzer]

I would prefer to say that it is an approimation for round coils. It's not that far wrong, and the steel in the cores tends to make it a better approximation. Remember, I was only agreeing with Bartolini, something I do not do that often. So if you want to argue that his patent write up is wrtong, go ahead, but David will not like it!

I think Mike's argument fails for round coils. If you imagine the diagram with circles instead of squares, the total area of the 5 small circles is less than the area of the big oblong thing that contains them, and the line segments don't cancel each other out any more, because they're not close together over their whole lengths.

[Mike Sulzer]

Is the purpose of this test to show that the series and parallel connection do not sound that different? Well, they should not differ by too much if you connect them to a load that is a lot lower than the inductive reactance at the harmonic frequencies. You have bad buzzing on the parallel test, and I am also not convinced that it was connected correctly. I thought that this might be a matter of how the test was conducted.

Nope. They are wired in series. And as I said multiple times, when I wired up all the coils on the Wal pickup in series (20k) it didn't sound anything like a two coil humbucker wound to 20k.

I think before any more speculation on what its inductance is, or isn't, goes on, some actual measurements should be done. I'd do it, but I don't own an inductance meter.

Judge for yourself:

http://www.sgd-lutherie.com/media/wal_test_series.mp3

The pickup was rigged up on one of my 5 string basses. It's a very tall pickup, so it was hitting the strings a little, and of course only covered 4 strings.

Here's the same pickup with the two rows in parallel

http://www.sgd-lutherie.com/media/wal_test_parallel.mp3

This was plugged direct into the board with no EQ. The mixer has a 10K impedance on the guitar input.

[David Schwab]

Plugging a 20k pickup into a 10k line input is hardly going to give a fair impression of its tone.

It's not a line input, it's a Hi-Z guitar input. I was in error about the input impedance, it's 1M. Not sure what I was thinking... The line inputs are 20k.

I think Mike's argument fails for round coils. If you imagine the diagram with circles instead of squares, the total area of the 5 small circles is less than the area of the big oblong thing that contains them, and the line segments don't cancel each other out any more, because they're not close together over their whole lengths.

Mike's argument fails because you can clearly hear that multiple smaller coils sound very different from that much wire on two large coils. The coils are in close proximity only in a very small area, and even then they don't touch. There's about 1/16" between them on their sides.

[David Schwab]

Is the purpose of this test to show that the series and parallel connection do not sound that different? Well, they should not differ by too much if you connect them to a load that is a lot lower than the inductive reactance at the harmonic frequencies. You have bad buzzing on the parallel test, and I am also not convinced that it was connected correctly. I thought that this might be a matter of how the test was conducted.

Mike, I can only think you are being difficult on purpose because I know you are not dense.

Those sound clips show that for a pickup who's DC resistance is 20k in series, it's very bright sounding. The parallel clip was just to show the difference. Then it's even brighter. Parallel connected coils are always brighter. That's common knowledge and reason for 4 conductor wiring used on pickups.

The original Wal Pro series had all the coils in series. I have the schematic right here. It did have a preamp, but there was a passive version as well. The preamp would have rendered a tone similar to my clips because of the buffering. A Guild or Gibson pickup, such as the ones I mentioned, would still sound like mud with a buffer. I know this from experience because I had the Gibson humbucker in my Ric with a JFET buffer.

If you don't think that matters, then I invite you to do some winding. Make a dual coil humbucker and wind each coil to 10K, and then wire them in series. Use a ceramic magnet and standard size steel screw poles, keepers, etc.

You will likely have to make the coils much larger than a PAF type since you wont fit that much wire on each one. A good approximation might be two overwound P-90s in series.

One thing ZI want to mentions is both Marko and myself have actually wound these types of pickups, and listened to what they do. While you made some single string pickups, you did not wind 10,000 turns of 42 on each bobbin. You actually have to do the work and can't rely on doing it through math because you don't have all the data.

Now if you actually had the pickups in hand and did some measurements to actually know what the inductance is with the coils in-situ, and then measured them in series and parallel, you would have some actual data, and not arm chair data.

These pickups are very time consuming to make, and I'm sure that if they didn't sound any different from two large coils, then the builders of such pickups wouldn't be bothered. But they do sound very different.

I don't care if you don't think it was connected correctly. The buzzing was due to the pickup being connected with alligator clips to a jack. The pickup has no shielding, and the strings on the bass were not grounded. That's electrical field noise, aka electrostatic interference. You know all about that. The pickup has 5 wires, two for each row, the analogy of a single humbucker coil, and a ground wire that grounds the poles. More than likely on the parallel test the ground wire was not making good connection when gathered with two other wires in the alligator clip. It was a quick and dirty test I did a couple of years ago to keep as a reference. It was my first time hearing what the pickup sounded like. I record everything.

But I have the pickup right here and can do the test over.

Also just to point out, Bartolini uses square bobbins and square cores. He seems to think the square cores make a difference. I haven't tried it so I have no comment, but Bill Bartolini seems to have settled on that through experimentation.