Dead Magnet

Discussion in 'Just Pickups' started by 61fury, Mar 23, 2016.

  1. Zepfan

    Zepfan Poster Extraordinaire

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    I guess if it wasn't for me experiencing a pickup working without strings and one bass working with nylon strings when they are supposed to have magnetic strings to work, and hearing in the past about current coming from the amp in a small amount coupled with my experiences with low voltage generators/electric motors/circuits, I might not question this.
    Since it is a fact that grid voltage is passed to the guitar, how do we know for sure that the pickups don't need the energizing voltage from the amp?
     
  2. Tony Done

    Tony Done Friend of Leo's

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    I can imagine a thought experiment. String enough of them up together and connect them to a torch bulb. Wave an iron bar over them and the bulb should light up. :) On a more practical level a strong pickup might be able to drive sensitive headphones; they will certainly drive a multimeter.
     
  3. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    One way we could know that the pickups don't require voltage from the amp would be to look at the principle they work on, and see that in other devices like an electric generator, where a moving magnet generates current in a coil with no source of power at all.

    IDK what "nylon string" bass you refer to, but what I've seen for long scale plastic strings on bass are the tapewound type where to outer wrap is plastic but the core is steel.

    Re: microphonic pickups and getting signal with no strings, AFAIK what we think of as movement may be different from what an atom thinks of as movement, where at an atomic level a vibration is a movement, so if the pickup is tapped on hard enough that you could feel the tap if you were holding it in your hand, or if you tap on the guitar body hard enough to feel it, there has been "movement" of the magnet and coil.

    If you reject the principle of a moving magnet inducing current in a coil with no outside source of current to begin with, then how does that help clarify the pickup producing signal without strings?
    A pickup without strings has no "moving parts", yet senses vibration.
    There still has to be some movement there, right?
    Take a dynamic mic that has a diaphragm attached to a coil near a magnet, where the smallest whisper will result in sound, from the smallest vibration that we might not consider movement, it's not much of a stretch to consider vibration of the magnet and coil in a pickup to be audible without strings. And more wax potting will reduce this sensitivity, while less or no wax will leave a pickup more microphonic. Even a well potted pickup is a little microphonic.
     
    Last edited: Apr 17, 2016
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  4. Zepfan

    Zepfan Poster Extraordinaire

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    The bass I was referring to was just one I saw in a video. Fender PBass with nylon strings. Wasn't aware they had a steel core. Have seen some guitars/basses with weed whacker line as well.

    I think I have a way to isolate the grid voltage from the amp to test this. One flow direction - Diodes to block inflow to the guitar and only allowing signal from the guitar to pass to the amp.
     
  5. Antigua Tele

    Antigua Tele Friend of Leo's

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    OK, this is nuts and it has to stop. I've done two experiments which disprove these notions:

    1) The false notion that the amp's supplied voltage is strong enough to induce meaningful magnetism in the pickup

    2) The false notion that the guitar can't create current without supplied (or "phantom") power.


    To start out, here's is a measured voltage coming from the amp:
    [​IMG]

    .022 volts.

    Here's a pickup coil with no magnet and no pole pieces:
    [​IMG]

    No magnetic field.

    Same pickup hooked up to the amp lead:

    [​IMG]

    No measured magnetism.

    So, there's that.

    Next, here's the voltage coming out of a guitar with the strings still:
    [​IMG]

    0.000 volts.

    Then I strummed the strings:
    [​IMG]

    .039 volts. It actually peaked closer to .045, but I could the the picture fast enough to capture it.
     
  6. Zepfan

    Zepfan Poster Extraordinaire

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    Calm down dude, it's just a discussion and not an argument.:cool:
    1st pic: did the same to 3 of my amps
    2nd pic: okay
    3rd pic: if that pickup is hooked up to the amp through the pictured cord it could still be energized by the amp.
    4th & 5th pic: did the same on my guitar with similar result, but wondered if the pickup still had field from bieng plugged in recently. The reason why I though it would be more revealing from a guitar that hasn't been plugged in for quite a while.

    Next test needed would be a guitar with isolation diodes on the jack to block grid voltage from the amp and see how the pickups react.
     
  7. Antigua Tele

    Antigua Tele Friend of Leo's

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    I want to be very clear: this is not an argument. This is about clearing up misconceptions. You'd think after nearly 70 years that the function of the electric guitar would be common knowledge, but alas, they are simple enough devices that people can get them to work without really understanding them, and so misconceptions have carried on for many decades.

    Thank you for laying out such a misconception so that we can address it.

    The pickup is energized by the amp, to the tune of .02 volts, as measured by image #1. And despite that, the gauss meter shows zero gauss; zero magnetism. While it is true that DC through a coil creates a magnetic field, it is so small in this case that it doesn't even register in the gauss meter. The AlNiCo pole pieces, by contrast, produce upwards of 1050 gauss at the ends.

    Do you understand what is being presented here?


    What do you mean "has a field from being plugged in recently"? The pickups have six strong AlNiCo magnets in them, there's simply no need to even consider the contribution of DC bias induced magnetism. I suspect that you're making a series of incorrect assumption about how electromagnetism works, and in turn, you are making statements which are hard to make sense of.
     
    Last edited: Apr 17, 2016
  8. Antigua Tele

    Antigua Tele Friend of Leo's

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    Here are a few more measurements illustrating how weak the magnetism is that comes from the DC offset of the amplifier:

    I have here a 9 volt battery, NOT YET connected to the pickup. The pickup has a single steel pole piece in it it aid in the formation of magnetic flux. I degaussed it to remove and residual magnetism it might have. Currently we're seeing 0 gauss.

    [​IMG]

    Now the 9 volt battery is hooked up. Note that 9 volts is orders of magnitude greater than the amp's DC offset at the input jack.
    [​IMG]

    Now we see only 12 gauss at the steel pole piece.

    By constrast, here' is a P-Bass pickup's AlNiCo pole piece:
    [​IMG]

    987 guass at this particular spot over the pole piece. They usually read 1050 more readily, these might have been sitting in a warehouse for a while before I got them.

    This demonstrates that the amplifier's DC offset has no meaningful contribution to supplying the magnetism that permits the guitar strings to produce magnetic induction in the coil. The coil windings would catch fire before they ever support the current necessary to equal the gauss supplied by the magnetic pole pieces.
     
  9. Deneb

    Deneb Tele-Afflicted Ad Free Member

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    Sir you do not seem that in order to measure the magnetic field in your system lacks the steel poles (or non-magnetized magnets)?
    If I have correctly understood the meaning of your experiment.
     
  10. Antigua Tele

    Antigua Tele Friend of Leo's

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    I'm not sure what you are asking, as I think you a word or two, BUT, what the steel pole does is provide permeability in the core of the coil. It doesn't provide magnetism, it merely aids it's creation. If I had left out the steel core, you just would have seen even less magnetism with the 9 volt battery.

    In other words, the pole piece is standing in for a nail in this demonstration:

    upload_2016-4-17_12-46-7.png

    In a regular guitar pickup, you have an AlNiCo or ceramic bar magnet underneath magnetizing the pole pieces, so again, the magnetic field is not only already there, but is orders of magnitude stronger than any magnetism that could be caused by the trace amount of voltage coming away form the guitar amp.
     
  11. Deneb

    Deneb Tele-Afflicted Ad Free Member

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    I have not seen your experiment with the 9 volt battery. I was in the process of writing question. Oops...
     
  12. Antigua Tele

    Antigua Tele Friend of Leo's

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    Sorry, that makes sense now.

    A magnetic field forms with or without a permeable core. It's regarded as an "air core" when there is no core. A permeable core magnetizes in the presence of another magnetic field (the magnetic field from the current carrying coil, in the case of an electromagnet), amplifying the overall amount of magnetism. A guitar pickup is actually a combination of air core and permeable core, since the pole pieces have gaps between them.
     
  13. Deneb

    Deneb Tele-Afflicted Ad Free Member

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    Can you know somebody tried to use an electromagnet in a guitar pickups?
     
  14. Antigua Tele

    Antigua Tele Friend of Leo's

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    It has never been done AFAIK. The first known electric guitar pickup made use of a horseshoe magnet, so they've been utilizing permanent magnets since the beginning. Producing an pickup that made use of an electromagnet would be technically challenging, and I'm hard pressed to think of any benefits it would provide.
     
  15. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Speakers used to use electromagnets though, so I suspect that it would be possible to make a pickup work with an electromagnet.

    It might be really really impractical though, where the speaker has close access to a power supply to charge an electromagnet, it would be harder to run power to the guitar.

    I had an Alembic bass with the 7 pin cable running to a power supply box plugged into wall voltage, that was a real pain in the butt.
    It was only to run the preamp, and the bass had two 9v batteries on board which could power one pickup without using the external power supply.
    It might be cool to have an adjustable electromagnet in the pickups to boost or cut output, not sure how much difference it would make though.

    Modern L ion batteries might make it almost practical.
    How much voltage would it take to produce the required gauss?
    Would the electromagnet coil induce hum in the pickup coil?

    Hey Deneb you can try this, right?
     
  16. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

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    If phantom power from the amp is necessary for a guitar pickup to work, then how do amps like the Mustang work? They, and many other amps, have coupling caps before the first amp stage.
     
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  17. Antigua Tele

    Antigua Tele Friend of Leo's

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    There shouldn't be since it's DC. You could use the same line for the power and the signal, like a phantom power microphone, but you'd have to use a balanced mic cable with your guitar.
     
  18. Zepfan

    Zepfan Poster Extraordinaire

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    { Good and glad to help out. LOL }

    { Yes. }


    { A coil can "hold" a field for a while. That field can act as a kick start for the circuit. That is what I thought to be the reason the pickup worked when strings weren't present. }
     
  19. Zepfan

    Zepfan Poster Extraordinaire

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    Your right about most people not knowing exactly how this works or have miss-conceptions of how they work and it's by these discussions and tests that we can learn and be sure how they work.
     
  20. Deneb

    Deneb Tele-Afflicted Ad Free Member

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    It is necessary to read the theory of electromagnets. Is it possible to create a compact and of sufficient power electromagnet with a battery 9 volt(or L ion batteries). And then create a pickup. But now I have not finished project with four guitars. I need to finish it.
    I will think about your offer.:)

    P.S.
    When I did not have information on active pickups (and seen them only in pictures), I was sure that a active pickups are made with an electromagnet. And the battery was provided for power supply a electromagnet in active pickups. And for this reason, the active pickups not had noise.:)
     
    Last edited: Apr 18, 2016
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