#1
I can't belive I never thought of this before. Instead of using permament magnets in pickups, why not simply use an electromagnet? Obviously batteries wouldn't be a viable option as they'd run down quickly, but if you used phantom power then it would be quite possible. Instead of using a standard volume setup which has treble rolloff and other issues, you could simply back off the power to the pickup and it would reduce the output. Equally, you could use the effect of differing pot values to your advantage. If you were to have a stacked pot, one half controlling magnet level (in addition to the master magnet level) and the other going directly to one side of the pickup, you could quite easily lower the resonant peak of a pickup (to take into account this variable, the pickup should have a naturally high resonant peak, giving you a useable range of sweep). Additionally, since there would be power going into the guitar, you could also use the magnet coils as a hum canceling feature, you'd have to zero the noise levels though for where you were.

I'm not saying that such an idea would be better than conventional pickups (it'd be a lot more hassle, at leasr) but just something different to fool about with. The clear advantage is that you could have either alnico or neodymium power at the flick of a switch.
Last edited by pot head pyro at Sep 29, 2010,
#3
It's a neat idea, although for the general guitarist, it's way too much of a hassle. And it would still probably sound different than a normal permanant magnet, even if it was at the same strength.


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#4
my motto about experimenting is this: you dont experiment for other people. you do it for yourself.

personally i'd be very interested in the results of this. regardless of if it is practical or not, it should be don by someone at least for the sake of learning.
#5
This would be an interesting experiment. However, while the magnet's strength would be variable, the coil would not, so not all settings would produce usable tones. It would go from too bright to too dark. Also, you need some way to account for the possible changes in volume, so you'd need to have some sort of preamp to take care of that.

What you could do is combine the variable magnet with a coil that has several taps, designed to provide a good match to the magnet strength settings. That way you'd have several pickups in one.

EDIT: Now that I think about it, there's a high risk of noise from the power supply, as any ripple in the DC supply to the magnet would be directly induced into the pickup coils and amplified.

Also, it would heat up. Not a good thing.
Last edited by sashki at Sep 30, 2010,
#6
Quote by sashki
This would be an interesting experiment. However, while the magnet's strength would be variable, the coil would not, so not all settings would produce usable tones. It would go from too bright to too dark. Also, you need some way to account for the possible changes in volume, so you'd need to have some sort of preamp to take care of that.

What you could do is combine the variable magnet with a coil that has several taps, designed to provide a good match to the magnet strength settings. That way you'd have several pickups in one.

EDIT: Now that I think about it, there's a high risk of noise from the power supply, as any ripple in the DC supply to the magnet would be directly induced into the pickup coils and amplified.

Also, it would heat up. Not a good thing.

Yeah, now that I think about it... That is what would happen/
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Quote by Anonden
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#7
I don't get it, what advantage is there to using an electromagnet rather than a permanent magnet? You'd be getting lots of noise with the electromagnet and you'd be wasting power.
#8
It would be an interesting novelty, but I'm not sure it's practical. Would be a nice experiment for sure, though.
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#9
Use a dump capacitor to smooth ripples? Like in rectification. Not sure of specifics but hey. I'm sure I saw something on geofex or summat about making sure power supplies were small. May not have been geofex, I can't remember.
#11
I seriously have no idea whether this would work or not but i think it might be a cool idea, a bit like a condenser microphone for your guitar or something?
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#12
Quote by sashki
This would be an interesting experiment. However, while the magnet's strength would be variable, the coil would not, so not all settings would produce usable tones. It would go from too bright to too dark. Also, you need some way to account for the possible changes in volume, so you'd need to have some sort of preamp to take care of that.

What you could do is combine the variable magnet with a coil that has several taps, designed to provide a good match to the magnet strength settings. That way you'd have several pickups in one.

EDIT: Now that I think about it, there's a high risk of noise from the power supply, as any ripple in the DC supply to the magnet would be directly induced into the pickup coils and amplified.

Also, it would heat up. Not a good thing.
I'm not sure if you see my point, if you were to have a naturally bright pickup and then simply shove a pot on the end of it in series then you could effectively change the peak frequency and other things (kinda like changing pot values in a guitar except more so), in laymans terms you could change the coils impedance and also the amount of signal going off to ground in the same way a volume pot shorts to ground. Secondly the "possible changes in volume" are entirely intentional since you would control the volume directly through the power of the magnet, that's not to say that you couldn't have a standard volume control too if you felt the need to have both.

As to hum, you would definitely need a very stable power source but that's by no means impossible, just about any amplifier used for audio is low ripple. Actually, having power going into the guitar could even be a good thing, if you were to send a reverse phase 60 cycle hum through the magnet coil then by dialing in the amount appropriate to the evironment you're in (some places have more magnetic interference than others so you'd have to tune it to where you were).
#13
You can get 1000uF low voltage caps cheaply. If you were to do it, you should use a VVR with a 1000uF, 100uF-220uF, 100nF, and 100pF caps in parallel. The lower value caps counteract the inductance of the higher value caps.

The heat of the electromagnet would play a role as well. If may be worth a shot. But if you wanna play with impedances, there are better ways to do it than to need power supplies besides a 9v battery.

I'd also argue that using a Neodymium magnet would be better, and simply vary the distance between the magnet and the pole pieces.
#14
Simply vary the distance between the magnet and the pole pieces? SIMPLY?

For a start how would you move the magnet at all? Options are gearing (which would be complex to install) from a 'pot' to the magnets, or servo motors, which would need power anyway.

Then you have to remember that field strength according to distance varies by an inverse square law, so the magent would be very sensitive to changes close to the pickup, and less senstive to those further away, whereas the field strength of an electromagnet has a linear relationship with the current passsing through it.

@ pot head pyro: Why would you have AC going into it btw?
#15
Quote by lozlovesstrats
Simply vary the distance between the magnet and the pole pieces? SIMPLY?

For a start how would you move the magnet at all? Options are gearing (which would be complex to install) from a 'pot' to the magnets, or servo motors, which would need power anyway.

Then you have to remember that field strength according to distance varies by an inverse square law, so the magent would be very sensitive to changes close to the pickup, and less senstive to those further away, whereas the field strength of an electromagnet has a linear relationship with the current passsing through it.

@ pot head pyro: Why would you have AC going into it btw?
If you mean the weak 60hz fluctuation deliberately put into the magnet coil, it's to cancel out 60 cycle hum. It works kinda in the same way as a humbucker, by phase cancelation. Basically what it's doing is un-doing what the background fields have done by producing exactly the same thing but in reverse phase.

Since we have power going into the guitar, making a circuit which would oscilate at 60hz wouldn't be too difficult. You could even make it so that the cap to smothe ripples was actually inside the guitar its self so that way you could get an exactl match of any little blips in the mains power before they're removed.

Also, given that you have powered magnetic coils, it would be fairly easy to implement it as a sustainer too. Just use a simple transistor amp to boost the output from the bridge pickup and then feed it back into the magnet coil of the neck pickup.
#16
Quote by pot head pyro
If you mean the weak 60hz fluctuation deliberately put into the magnet coil, it's to cancel out 60 cycle hum. It works kinda in the same way as a humbucker, by phase cancelation. Basically what it's doing is un-doing what the background fields have done by producing exactly the same thing but in reverse phase.

Since we have power going into the guitar, making a circuit which would oscilate at 60hz wouldn't be too difficult. You could even make it so that the cap to smothe ripples was actually inside the guitar its self so that way you could get an exactl match of any little blips in the mains power before they're removed.

Also, given that you have powered magnetic coils, it would be fairly easy to implement it as a sustainer too. Just use a simple transistor amp to boost the output from the bridge pickup and then feed it back into the magnet coil of the neck pickup.



You'd only cancel out the 60hz osculation if the phase angle on the signal you're generating exactly matches the utilities' (well 180 degree phase shift really). If you're getting power from the wall, that's not hard to do. If it's battery powered, eh not so easy.
#17
Quote by earthwormjim
You'd only cancel out the 60hz osculation if the phase angle on the signal you're generating exactly matches the utilities' (well 180 degree phase shift really). If you're getting power from the wall, that's not hard to do. If it's battery powered, eh not so easy.
If it's battery powered then it wouldn't be practical, it'd have to run on phantom power, from which you could get the exact 60 cycle hum.