Active magnets?

[R.G.]

The earliest speakers were "electrodynamic" - the magnetic field was caused by current in a winding.

Any pickups made that way?

It seems like the charging field would have to be a current source to avoid loading effects on the signal from transformer action, but that would offer yet another degree of control. Your pickups would have dialable sensitivity.

It's possible that the pickup coil itself coil could do the field charging if done right, I think.

Any history?

[black_labb]

i dont know if its been done, but i can imagine the coils from the electromagnet would effect the sound in the same way metal covers do, but probably alot more. having said that, im sure it would be quite different.

[soundmasterg]

Just off the top of my head, I would think that an arrangement like that would hum more. I may be wrong, but if the hum would result, that wouldn't be good for anyone!

greg

[R.G.]

Just off the top of my head, I would think that an arrangement like that would hum more. I may be wrong, but if the hum would result, that wouldn't be good for anyone!

greg

Why should it hum more?

Hum pickup is the result of a coil of wire living inside the ever-present power line EM field. For a coil fed DC by a current source, unless the current source itself had a hum component, the current source induces no hum. The current source has a very high impedance 'cause that's what current sources do, and so it does not load the coil. The coil still cuts the same flux lines in the external hum field that it did before. Hum should be the same.

Granted, one could botch the wiring and induce more hum pickup that way, but that's true of every wiring setup of every kind.

[David Schwab]

I saw a patent for a very early guitar pickup which didn't have a permanent magnet. The guitar had a switch, and first you set it so the coil acted as an electromagnet, which magnetized the strings, and then you switched it to work as a pickup.

I think this is the only time I've seen an electromagnet used.

The only thing I can think of that might be an issue is heat. I remember making some electromagnets when I was a kid and they got hot, but I suppose it's all relative to the amount of current you are putting into it.

I used to think it might induce hum into the string sensing coils also, but you are right that clean DC power shouldn't do that.

Could be an interesting thing to try.

[Ruel]

If any of you guys are thinking of doing and then marketing it later, you've got to act fast before DiMarzio puts out a patent for it. Or maybe somebody has patented it already?

[R.G.]

By publicly disclosing it here, I've established the date of it being conceived. DiMarzio would have to commit criminal fraud in backdating evidence of previous conception to obtain a patent.

I have one year from the date I posted that to file for a patent (assuming I would... ) and unless someone can show they came up with it first, It's not patentable by others. After the year, it's public domain.

I am not a lawyer - but I've had to listen to a lot of them.

[Sock Puppet]

After discovering that Google has a patent search (whatever next?), found this from 1935/36:

http://www.google.com/patents?id=QoM...trings#PPP2,M1

S.

[Alex/Tubewonder]

Sustainer by Fernandes is using an electromagnet as string excitation device. So it's an inverse function to a pick up but still the basic principle is the same.

[R.G.]

After discovering that Google has a patent search (whatever next?), found this from 1935/36:
S.

Yep, I knew they did that, the idea being to magnetize the strings. However, on reading the full patent, I find that the original inventor tried and discarded using direct current in the pickups at the same time based on noise. I think that establishes prior art, so a new patent would have to at least include a noise reduction means to pass the "novel" test. But it is possible that it is inherently noisy, I'll have to do more research.

Sustainer by Fernandes is using an electromagnet as string excitation device. So it's an inverse function to a pick up but still the basic principle is the same.

Actually, it's not.The sustainer uses a permanent magnet to establish a steady field pulling on the string, just like a normal pickup. By driving the winding the sustainer alternately relaxes and enforces the existing pull on the strings, giving a magnetic field drive to the string. The string vibration is picked up by another normal pickup by the variable reluctance method as normal.

[David Schwab]

After discovering that Google has a patent search (whatever next?), found this from 1935/36:

http://www.google.com/patents?id=QoM...trings#PPP2,M1

S.

Yep, that's the one. I lost the patent on that one.

[David Schwab]

Yep, I knew they did that, the idea being to magnetize the strings. However, on reading the full patent, I find that the original inventor tried and discarded using direct current in the pickups at the same time based on noise. I think that establishes prior art, so a new patent would have to at least include a noise reduction means to pass the "novel" test. But it is possible that it is inherently noisy, I'll have to do more research.

I've been saying it would be noisy, but I'm not sure why I thought that. I might have read that patent, or it might have been from experiments I did years ago. I tried so many things back in the 70's that I don't remember most of them!

But I'm starting to recall trying something like this and it did indeed hum. I suppose the magnet coil resonates?

Another thing I was messing with back then was sending some signal into a coil adjacent to the pickup coil, to change the resonance.

I had a working sustainer in 1977... but it was an acoustic, not a magnetic type. It was built into a tune-o-matic bridge.