Bar Magnets & Blade Pickups

[raygun85]

Is there any reason why we should use a steel blade instead of just turning the bar magnets up on their side?

[Sportbernd]

Different sound character?! Space?!

[Mike Sulzer]

Is there any reason why we should use a steel blade instead of just turning the bar magnets up on their side?

The use of steel as pickup core(s) dates from before there was alnico, and it required a larger external magnet to get the necessary field strength. But steel also has a higher permeability than most permanent magnetic materials and so it helps concentrate the flux lines from the vibrating strings. This is not a huge effect, although it does partly explain why humbuckers have a higher output than Fender SCs, and so it provides a reason for continuing to use steel. Also, the eddy currents induced in the steel have an effect on the pickup circuit, producing effects that could be difficult to achieve in any other way.

[David Schwab]

Is there any reason why we should use a steel blade instead of just turning the bar magnets up on their side?

Some pickups use an alnico bar as a blade. These include the old Gibson Firebird/Thunderbird pickups and the EMG SA.

You will get a different tone than when you use steel blades. The steel warms the sound up.

[FunkyKikuchiyo]

I looked into it a while ago, and I remember people citing a couple problems, though I can't attest to their validity. One is that the magnets will lose charge without a keeper, getting the correct amount of charge to not pull the string like crazy is tricky, and sourcing the materials makes it hard for those of us who are on a shoe string budget. I have doubts on these arguments, but they seem to be popular ones.

[raygun85]

Thanks for the response, guys. I've done a ton of research on the net and came up with zilch. Just wanted a straight answer. Thanks again.

[fieldwrangler]

You will get a different tone than when you use steel blades. The steel warms the sound up.

+1.

[salvarsan]

I looked into it a while ago, and I remember people citing a couple problems, though I can't attest to their validity. One is that the magnets will lose charge without a keeper, getting the correct amount of charge to not pull the string like crazy is tricky, and sourcing the materials makes it hard for those of us who are on a shoe string budget. I have doubts on these arguments, but they seem to be popular ones.

Not to worry.

The early AlNiCo alloys had problems. A5 and higher hold their magnetism well enough for a few decades or more.

Remanence is the magnetic field strength, but it's half the story in describing magnets.
Coercivity describes how well something holds its magnetic field.

You know that A2,3,4 aren't so good, and their coercivity figures show it.
Use A5 and higher, or ceramics, or rare earth magnets and it's less of an issue.

-drh

[David Schwab]

One is that the magnets will lose charge without a keeper

An easy fix is to have a steel plate under the pickup connecting both magnets.

But Strat magnets don't go dead. I guess the longer they are, the better.

[FunkyKikuchiyo]

But Strat magnets don't go dead. I guess the longer they are, the better.

As I recall from a post from Frank Falbo at one point, it is a question of ratios. Their rule of thumb was 5:1, and depending on how thick you want a blade, that could get violated. I'm not sure how that third dimension would play in being a long blade instead of a rod.

Salvarsan - thanks for the clarification! I had indeed been overlooking that data for a while, and tended to consider all alnico to be roughly the same coercivity.

I will add for other readers that using ceramic or rare earth blades would solve that problem but cause a myriad of other problems, namely too much string pull, assuming the design isn't altered to account for their mammoth strength. I tried a couple things but had no luck, and the folks on here who HAVE had luck have encapsulated the magnets into something, but that seems to deviate from the proposition in the OP. Mr. Candy's epoxy resin magnets could work well for this, eh?

I may have to try some A5 or A8 blades at some point... hmmm....

[David Schwab]

As I recall from a post from Frank Falbo at one point, it is a question of ratios. Their rule of thumb was 5:1, and depending on how thick you want a blade, that could get violated. I'm not sure how that third dimension would play in being a long blade instead of a rod.

It would be how tall, not thick, in the case of a blade. It's all about how far the two poles are from each other.

You figure it has to be as tall as the bobbin, and that's tall enough.

Where they have problems is very narrow magnets, like for the dual blade pickups. Those magnets are

[FunkyKikuchiyo]

It would be how tall, not thick, in the case of a blade. It's all about how far the two poles are from each other.

It is a radio..... so, height and thickness.