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Faraday Cage: Would This do the trick?

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tntero

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So, im a guitar player, and as you might know, electric guitars, use magnetic pickups to "capture" the frequencies of the strings.

There is a different kind of pickup, which is not actually a pickup, its called a sustainer, and basically, it takes the signal of the pickups and amplifies it to a coil that induces the strings into moving, therefore creating an infinite sustain and causing the sound to last for ages as long as it is on.

As an intermediate electronics apprentice, i want to do one myself, mostly because the originals cost around 200$...

What concerns me is that they say in the website of the original product that the driver has to be more than 2 inches away from the pickup, but the way i want to put it, it is closer than that. I assume that they say it has to be 2 inches away because the driver would mess up the sound coming from the pickup by changing its magnetic field.

I've been reading about faraday cages, i read that shoplifters often use tin foil to block the magnetic RFID sensors, that got me wondering, would i be able to "block" the magnetic field if i wrapped the driver in tin foil?

Also, would i have to connect the tin foil to ground to prevent humming?

Last but not least: Whats the best way to wrap a coil like this one: **broken link removed**

I need to wrap the pickup with a heavier gauge wire, otherwise the current flowing through it would damage the amplifier circuit of the sustainer. (this is because i will use a regular guitar pickup instead of wrapping a coil from scratch, for aesthetic reasons)

Thanks in Advance
Antero Duarte
 
RFID uses electromagnetic (radio) waves, not magnetism, so it's not comparable to this.

I don't see why you'd need any shielding at all. After all, you can control the amplitude of the magnetic driver (the coil driving the strings, not the pickup coil), so if it's too strong, just turn it down. Any problem with that you can see?
 
Generally, a Faraday cage is used to block electric fields.

The Faraday cage could be built from aluminium or copper, which would not do much for a magnetic field.

In days gone by, mumetal was used to make magnetic screens and I think a piece of mumetal wrapped around your sustainer could do what you want.

Where to get some mumetal, I do not know. I cannot ever remember seeing it on sale anywhere.

However, if you can find an old CRT based oscilloscope which is scrap, try using a piece of the metal shield from around the neck of the tube, they are usually made from mumetal.

JimB
 
RFID uses electromagnetic (radio) waves, not magnetism, so it's not comparable to this.

I don't see why you'd need any shielding at all. After all, you can control the amplitude of the magnetic driver (the coil driving the strings, not the pickup coil), so if it's too strong, just turn it down. Any problem with that you can see?

oh i see xD

the aplitude thing: there might be a problem with that, you see, typical guitar strings are not really the easiest thing to move by inductance, so, first if i reduce the amplitude of the driver, the sustain will not be infinite, and second, it might not even work at all.

you dont happen to have any idea on how i could "isolate" the magnetism in the driver coil, do you?

thanks
 
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Generally, a Faraday cage is used to block electric fields.

The Faraday cage could be built from aluminium or copper, which would not do much for a magnetic field.

In days gone by, mumetal was used to make magnetic screens and I think a piece of mumetal wrapped around your sustainer could do what you want.

Where to get some mumetal, I do not know. I cannot ever remember seeing it on sale anywhere.

However, if you can find an old CRT based oscilloscope which is scrap, try using a piece of the metal shield from around the neck of the tube, they are usually made from mumetal.

JimB

that sounds like the best option so far, only oscilloscopes have these mumetal shielding? or could i get it from any other CRT based monitor? say a computer screen? i can get those fairly easily

thanks for your time
 
could i get it from any other CRT based monitor? say a computer screen?
Unlikely, for the last 60 years TVs and CRT based computer monitors have not had magnetic screening around the tube necks.
Probably because there are no magnetic fields close enough to cause a problem.

An oscilloscope however is usually build as compact as possible and so the magnetic screen is used to minimise the effects of stray magnetic fields from the mains transformer.

JimB
 
the aplitude thing: there might be a problem with that, you see, typical guitar strings are not really the easiest thing to move by inductance, so, first if i reduce the amplitude of the driver, the sustain will not be infinite, and second, it might not even work at all.

you dont happen to have any idea on how i could "isolate" the magnetism in the driver coil, do you?

I think you're a little confused as to what you really want.

As I understand it (and I could be wrong!), what you're trying to do here is to physically stimulate guitar strings by electromagnetism. So far, so good.

I would think you'd want to do this with the coil as close to the string as practical, so as to focus the magnetic field directly on the string. Of course, at the same time, you want to avoid having that field impinge on the guitar pickup; you want to pickup to pick up the string's vibration, not the magnetic field from the induction coil.

Good so far? So I really have no idea where exactly you'd want to put the coil: I'm guessing somewhere between the pickup and the end of the neck, far enough away from the pickup not to couple to it magnetically, but close enough to the center of the string to be able to influence it.

Presumably, you're going to have control over the strength of the field you induce, like a "volume control" for the coil. Heck, why don't you just try it? Position the coil where you think it'll do the most good, then use the amplitude control to fine-tune the coil, so it drives the string sufficiently without overdriving it or coupling to the pickup (which I assume will result in feedback).

Does this make sense?
 
What concerns me is that they say in the website of the original product that the driver has to be more than 2 inches away from the pickup, but the way i want to put it, it is closer than that. I assume that they say it has to be 2 inches away because the driver would mess up the sound coming from the pickup by changing its magnetic field.

Antero Duarte

That's where he wants to put it.
 
What I'm saying is that before the O.P. goes to all the trouble and expense of locating mu-metal shielding, why don't they just try it and see what happens? It seems to be that by controlling the strength of the inductive coil (and there has to be a way to do that, otherwise the whole thing's pretty useless), they may be able to get it to work without needing any shielding.
 
actually, something like this might work, you need one per string. the pole pieces being so close together takes care of limiting the spread of the magnetic field. it also doubles the efficiency by using a "push-pull" action. there was a device long ago called an E-Bow that worked like this.

edit: i stand corrected, they still make it..... the E-bow has a pickup coil, amplifier and driver coil in 1 simple package...
 

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What I'm saying is that before the O.P. goes to all the trouble and expense of locating mu-metal shielding, why don't they just try it and see what happens? It seems to be that by controlling the strength of the inductive coil (and there has to be a way to do that, otherwise the whole thing's pretty useless), they may be able to get it to work without needing any shielding.

my plan is to do that, i just wanted to know your opinion, in case it went go wrong, i would already have the answer for my problem xD see what i mean?
 
actually, something like this might work, you need one per string. the pole pieces being so close together takes care of limiting the spread of the magnetic field. it also doubles the efficiency by using a "push-pull" action. there was a device long ago called an E-Bow that worked like this.

edit: i stand corrected, they still make it..... the E-bow has a pickup coil, amplifier and driver coil in 1 simple package...

i am familiar with the e-bow, and that design is pretty interesting, but the thing is, i wanted to use the regular pickup casing because it will look like a regular guitar.
 
...

In days gone by, mumetal was used to make magnetic screens and I think a piece of mumetal wrapped around your sustainer could do what you want.

Where to get some mumetal, I do not know. I cannot ever remember seeing it on sale anywhere.

However, if you can find an old CRT based oscilloscope which is scrap, try using a piece of the metal shield from around the neck of the tube, they are usually made from mumetal.
...

I just wanted to add that most of those cheap little PC speakers made to sit next to your monitor have that metal shielding inside. They are usually easy to find as junk and safe enough to pull apart.
 
What I'm saying is that before the O.P. goes to all the trouble and expense of locating mu-metal shielding, why don't they just try it and see what happens?

Exactly what I was going to suggest.

If you build it and it then needs tweaking you've not lost any money as you'll have had to build it anyway. If it doesn't need tweaking then you're quids in !
 
Electronics Goldmine has some one-side adhesive Ultraperm 80 available; it's similar to mu-metal but has no copper in it:
https://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A

Just kind of thinking out loud here; but I believe the closer you get to the bridge with the sustainer, the more power it's going to need to keep the strings vibrating, just due to the loss of mechanical advantage.

But... I don't see how you'll be able to put them both in a standard pickup housing, even if you DO use shielding.
 
Just kind of thinking out loud here; but I believe the closer you get to the bridge with the sustainer, the more power it's going to need to keep the strings vibrating, just due to the loss of mechanical advantage.

Right, which is why I said (wrote) that ideally you'd be as close to the center of the string as possible. Musically speaking, activating the string (by bowing) close to the bridge is called sul ponticello, which yields a wispy, hollow sound, probably not what you want.
 
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the other way to accomplish what you are trying to do is to mount a "wall driver" magnetically on the back of the guitar. a wall driver is a speaker, but the cone has been replaced with a steel plate or a large ferrite magnet. when stuck to a piece of steel plate (usually mounted on a wall, but could be on the back of a guitar), the vibrations produced turn the whole surface into a speaker. it's a variation of Jimi Hendrix's technique of butting the guitar up on the front of a speaker cabinet to get lots of sustain.
 
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