Brass bobbin -- what do you all think?

[Wrnchbndr]

I'm still new to this forum so I'm not sure that I did the upload attachment properly. I've wound one of these but was very disappointed at the result. The alnico slugs are from stewmac and I followed their direction for charging the magnets but I think the magnets are weak and thus the poor outcome. Now that I have a new winder, I was thinking of rewinding them a bit more consistently and sending them to Lindy Frailin to be charged on his evil scientist magnetic charger. In person, they look great but I'm not sure if the brass is killing the pickup.

Thoughts?

[David Schwab]

I remember this from MIMF. It's the eddy currents that gave you a dull tone. You'll see that the PAF makers here also hate brass covers and bass plates.

As a test you can saw the brass top down the middle between the D and G strings, to make it two halves, and that should make it a little brighter. The reason for that is you decreased the surface area of the brass.

Unless you make them very thin, the brass will dull the tone.

[Rosewood]

Looks good even if it don't sound good. I started to do an aluminum version of that but never got around to it. Would the eddy currents be the same for all metals?

[David Schwab]

Looks good even if it don't sound good. I started to do an aluminum version of that but never got around to it. Would the eddy currents be the same for all metals?

The more conductive, the worst. Seth Lover wanted Stainless Steel for the PAF covers, but settled on Nickel Silver, both of which would be better than brass or copper. I think Aluminum would be pretty bad.

But.. if you design the pickup with that metal bobbin in mind, it might be interesting. Maybe.

[Possum]

yikes....

yeah that brass is going to soak up the treble real bad espcially with the coil right up against it and the magnets sunk in it like that. bad idea, but cool looking. I am working on a prototype pickup and one thing I tried was using a brass plate as the top bobbin flat, same thing, it really dulled the pickup down bad. I was trying to simulate having a metal cover over the coil but this really didn't work at all...

[jack briggs]

I'm curious as to the effect of covers in general on humbuckers.

We all know how the same pickup with a cover tends to be somewhat dampened in highs compared to without, but I'm trying to grasp the logic behind why we don't hear a greater imbalance of coils (and therefore more clarity) because of the cover's affecting the magnetic field of the slug poles while leaving the screw poles open and seemingly unaffected.

Does this make sense to anyone else?

[David Schwab]

but I'm trying to grasp the logic behind why we don't hear a greater imbalance of coils (and therefore more clarity) because of the cover's affecting the magnetic field of the slug poles while leaving the screw poles open and seemingly unaffected.

Because that's not what's going on. The cover isn't blocking the field from the slugs, and allowing the screws through. It's actually creating its own field which is opposing the fields from the main magnet... slugs or screws.

The cover is actually magnetically neutral. An iron or steel cover would block the magnetic field. But the cover is conductive, and in the presence of a magnetic field small electrical currents flow on the surface (eddy currents) and all flowing currents produce magnetic fields (and vice versa). These small magnetic fields oppose the field that created them (like bad children), and the effect is loss of high frequencies, probably because impedance increases with frequency, so the highs are always first to go!

[Wrnchbndr]

David, I'm glad you're here. You seem to have an understanding of the foundations involved. There is so much available information on the higher levels of technology that some of this foundational stuff is almost alchemy. If I'm reading this right, at a basic level, its mass of non-ferrous conductive material that we should avoid -- a little is okay or at least tolerable???

I'm still going to have the slugs magnetized properly. Even using the x-actoblade technique to measure magnetic strength, its easy to tell that the slugs are patheticly weak. Maybe with an active preamp the pups will have a redeaming quality of some sort. They look so cool. I have a very basic X/Y table on my drill press and doing this is very easy and the opportunities for variations are endless.

[jack briggs]

Because that's not what's going on. The cover isn't blocking the field from the slugs, and allowing the screws through. It's actually creating its own field which is opposing the fields from the main magnet... slugs or screws.

The cover is actually magnetically neutral. An iron or steel cover would block the magnetic field. But the cover is conductive, and in the presence of a magnetic field small electrical currents flow on the surface (eddy currents) and all flowing currents produce magnetic fields (and vice versa). These small magnetic fields oppose the field that created them (like bad children), and the effect is loss of high frequencies, probably because impedance increases with frequency, so the highs are always first to go!

David,

Thanks for the reply. But, I've got to ask - wouldn't a steel or iron cover actually not block but spread the magnetic field, the material itself being magnetically attractive?

Also, why is copper used as a magnetic insulator? You see them in almost every tube guitar amp.

Don't the copper bottom plates on some early Tele bridge pups actually spread the field? Or are they just copper plated steel?

Also, if covers are magnetically neutral, why would nickel silver ones make that much of a difference versus brass or copper? After all, the main difference between nickel silver and brass is the addition of nickel.

Just trying to get a grasp on this - thanks for your help.

[soundmasterg]

Also, why is copper used as a magnetic insulator? You see them in almost every tube guitar amp.

I'm not sure what you're talking about here. Copper wiring is used in tube amps to connect everything together. Brass plates are used as a grounding buss. In PCB's, copper is used as one of the planes in the boards to connect things together. I don't know where you get that copper is used as a magnetic insulator though?

Also, if covers are magnetically neutral, why would nickel silver ones make that much of a difference versus brass or copper? After all, the main difference between nickel silver and brass is the addition of nickel.

I'm not sure of the exact reason why the nickel silver ones sound better and make such a difference as compared to brass covers, but they do. I would expect it has something to do with the eddy currents and the losses of each metal. Perhaps Enzo or someone along those lines could elaborate if they know. Personally I can't stand brass covers in humbuckers. They sound harsh and unbalanced.

Greg

[David Schwab]

David, I'm glad you're here. You seem to have an understanding of the foundations involved. There is so much available information on the higher levels of technology that some of this foundational stuff is almost alchemy. If I'm reading this right, at a basic level, its mass of non-ferrous conductive material that we should avoid -- a little is okay or at least tolerable???

You can have covers, but they need to be thin and certain materials are better than others. Same is true for base plates. Like Possum said, probably having the brass so close to the coil makes matters worse.

I'm learning this stuff along with everyone else here.

I'm still going to have the slugs magnetized properly. Even using the x-actoblade technique to measure magnetic strength, its easy to tell that the slugs are patheticly weak. Maybe with an active preamp the pups will have a redeaming quality of some sort. They look so cool. I have a very basic X/Y table on my drill press and doing this is very easy and the opportunities for variations are endless.

I use the refrigerator test, using a known pickup as a baseline. lol I have to get a Gauss meter one day soon.

I'm sure if you get the magnets fully charged it will help.

[David Schwab]

David,

Thanks for the reply. But, I've got to ask - wouldn't a steel or iron cover actually not block but spread the magnetic field, the material itself being magnetically attractive?

Well steel is used for pole pieces, and in some cases as baseplates, as in the Burns Tri-Sonics. But if you put a piece of steel over the poles, the flux field will travel into that steel, and not to the strings, unless it is shaped to direct the field.

Also, why is copper used as a magnetic insulator? You see them in almost every tube guitar amp.

I've never seen that. I would think it's a shield, but not a magnetic shield.

Don't the copper bottom plates on some early Tele bridge pups actually spread the field? Or are they just copper plated steel?

I believe they are copper pated steel. I think the original reason for them was shielding, along with the metal bridge plate and ash tray bridge cover.

Also, if covers are magnetically neutral, why would nickel silver ones make that much of a difference versus brass or copper? After all, the main difference between nickel silver and brass is the addition of nickel.

I brought that up a bunch of times too. Apparently nickel silver is less conductive, even though nickel is magnetic.

[black_labb]

pretty sure the nickel silver has less of an effect is because it has higher resistance, meaning less eddy currents. atleast ive heard that around a fair bit.

[jack briggs]

David,

Thanks for your insights.

Some of you must have seen a pad of copper placed on the side of a PT in a tube amp before?!? It's there for shielding either EMI or RF or both. That was my point about copper in an amp.

[black_labb]

David,

Thanks for your insights.

Some of you must have seen a pad of copper placed on the side of a PT in a tube amp before?!? It's there for shielding either EMI or RF or both. That was my point about copper in an amp.

i believe that is to ensure that each of the layers of the iron is connected to ensure that they are each grounded correctly.