Teach me a little about iron loading

[Mark Hammer]

Magnetism in general baffles me. Hell, I think I understand women better than I understand magnetism. And that's not saying much.

Having said that, let us say I had a single-coil pickup using six alnico pole-pieces - perhaps you have seen such a very pickup in your lives! - and I stuck an iron bar on the bottom of it, such that all those polepieces were magnetically coupled. What sort of outcome should I, or might I, expect from doing that?

Does the effect of such coupling radically change the basic tone, or merely shape it a little?

Does the composition, or any other physical properties, of such a "bar" matter at all, or is the mere fact of having used one the lion's share of what I might expect to change, and any other characteristics mere details?

Are there existing commercial examples of this in action? (apart from Tele bridge pickups)

[big_teee]

Hopefully we can keep this in laymens terms.
If it gets too gifted and talented, I'll move it to the Main forum.
Steel in a pickup adds Eddie currents.
I've tried it with strat bridge pickups, I usually like them better without the steel.
If you use steel, most put tape between the magnets and the steel plate.
Tape and wax potting helps control the microphonics.
I use the tape on Tele bridge pickups with the steel baseplates.
Steel baseplate should make the pickup less bright, increase the mids and bass.
T

[Mark Hammer]

Thanks T.

Am I correct in assuming that the tape on the Tele baseplate goes between the pickup and baseplate, and is to damp any micro-vibration involving the baseplate hitting the polepieces, kind of like the role that surgical tubing around pickup mounting screws is presumed to play?

And, following up on a different thread here, would a laminated baseplate be better than a thicker solid one?

[big_teee]

Thanks T.

Am I correct in assuming that the tape on the Tele baseplate goes between the pickup and baseplate, and is to damp any micro-vibration involving the baseplate hitting the polepieces, kind of like the role that surgical tubing around pickup mounting screws is presumed to play?

And, following up on a different thread here, would a laminated baseplate be better than a thicker solid one?

I use the narrow paper humbucker tape between magnets and baseplate.
Not sure the laminated would benefit or not.
Maybe others will jump in.
T

[Joe Gwinn]

Am I correct in assuming that the tape on the Tele baseplate goes between the pickup and baseplate, and is to damp any micro-vibration involving the baseplate hitting the polepieces, kind of like the role that surgical tubing around pickup mounting screws is presumed to play?

Making sure that there can be no vibration between polepieces and baseplate sounds like a very good idea, to prevent squealing. Tape is one way, wax is another, epoxy is yet another.

And, following up on a different thread here, would a laminated baseplate be better than a thicker solid one?

No, it would be no better (because the laminations are perpendicular to the coil axis, so there is no reduction of eddy currents) to worse (because a laminated baseplate is a factor floppier than a solid baseplate - stiffness varies as the cube of thickness).

[big_teee]

Making sure that there can be no vibration between polepieces and baseplate sounds like a very good idea, to prevent squealing. Tape is one way, wax is another, epoxy is yet another.



No, it would be no better (because the laminations are perpendicular to the coil axis, so there is no reduction of eddy currents) to worse (because a laminated baseplate is a factor floppier than a solid baseplate - stiffness varies as the cube of thickness).

Thanks Joe:
I tape between magnet and baseplate then wax.
I've had issues with tele baseplates, without tape even waxed.
If there is any movement of the baseplate, or if the fiber is not straight, so I found it easier to tape and wax.
Nothing is more frustrating to get a tele with through body stringing all put together, to find out you have microphonic issues with the baseplate.
Another problem I've had with Teles is if the pickup hole is not routed enough and the edge of the baseplate hits, or rides against the body.
I had one that drove me crazy before I figured out it was apparently vibrating against the body.
The dremel tool cured that.
T

[Joe Gwinn]

I tape between magnet and baseplate then wax.
I've had issues with tele baseplates, without tape even waxed.
If there is any movement of the baseplate, or if the fiber is not straight, so I found it easier to tape and wax.
Nothing is more frustrating to get a tele with through body stringing all put together, to find out you have microphonic issues with the baseplate.

I bet. It occurs to me that it the thickness of the gap between polepieces and steel baseplate may matter, and wax alone didn't yield a sufficient gap and/or didn't fix the separation solidly enough. The smaller the gap, the larger the relative effect of a given vibration.

I'd be tempted to use a piece of 0.010" fishpaper (which is basically really thin forbon) between the bobbin and the baseplate, and wax everything together.

Another problem I've had with Teles is if the pickup hole is not routed enough and the edge of the baseplate hits, or rides against the body.
I had one that drove me crazy before I figured out it was apparently vibrating against the body.
The dremel tool cured that.

That would do it. In both meanings.

[ric]

I wonder about other types of metal, of the types that interact magnetically. Any thoughts on that, folks?

[big_teee]

Fender, used regular masking tape on 70s grey bottom tele bridge pickups.
I rewound a couple a while back, and I reused the original masking tape.
put a little more glue on it and left it original.
I have always been tempted to try a tele bridge without the steel baseplate.
It requires different flatwork with threaded holes in the forbon.
Regular forbon for steel baseplates, is drilled out with large holes.
T

[Mike Sulzer]

Add a bar and the dc field rises by about 5%. Certainly you have altered the flux lines, and you could see what this is like using FEMM. I will check the impedance (change in the effect of eddy currents) when I get chance.

Magnetism in general baffles me. Hell, I think I understand women better than I understand magnetism. And that's not saying much.

Having said that, let us say I had a single-coil pickup using six alnico pole-pieces - perhaps you have seen such a very pickup in your lives! - and I stuck an iron bar on the bottom of it, such that all those polepieces were magnetically coupled. What sort of outcome should I, or might I, expect from doing that?

Does the effect of such coupling radically change the basic tone, or merely shape it a little?

Does the composition, or any other physical properties, of such a "bar" matter at all, or is the mere fact of having used one the lion's share of what I might expect to change, and any other characteristics mere details?

Are there existing commercial examples of this in action? (apart from Tele bridge pickups)

[Mark Hammer]

Thanks, Mike. Much appreciated. And from your other comments regarding Tele bridge baseplates, I gather any such bar needs to be properly protected against microphonic vibrations.

[Joe Gwinn]

I wonder about other types of metal, of the types that interact magnetically. Any thoughts on that, folks?

The fact that even touching the wooden body of the guitar caused a problem implies that any contact will be a problem, regardless of material, probably because the contact causes much higher frequencies than the original vibration, and so are that much more audible.

[Mike Sulzer]

And here is the comparison between "bar" and "barNone" (barNonebar.pdf). There is some increase in loss due to eddy currents; the yellow line in the "bar" case is further below the dashed line than the "barNone" case. This is not a huge effect, but I think if you can measure it, somebody can hear it, and might like it better one way than the other.