What kind of electricity??

Discussion in 'Tech-Talk' started by Steelskin, Feb 17, 2009.

  1. Steelskin

    Steelskin Strat-Talker

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    Im am thinking about a new project, and im wondering...

    When a pickup puts out a signal, what type of electricity is it? I tried to get a reading from the guitar. PLucking a string a putting my meter on it but tried both ac and dc and got nothing..

    Does it have to be pluged into an amp to generate a signal? I thought the amp just amplified that signal.

    Any help is apreciated.
     
  2. Steelskin

    Steelskin Strat-Talker

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    I did some searching, based on what type of caps are used im going to say... DC..... am i wrong?
     
  3. Poseidon9447

    Poseidon9447 Strat-O-Master

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  4. Jefro

    Jefro Senior Stratmaster

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    I'd have to guess DC because I can't think of any reason for it to alternate "AC".
     
  5. Poseidon9447

    Poseidon9447 Strat-O-Master

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    [edit] Magnetic pickups
    A magnetic pickup consists of a permanent magnet such as a AlNiCo, wrapped with a coil of a few thousand turns of fine enameled copper wire. The pickup is most often mounted on the body of the instrument, but can be attached to the bridge, neck and/or pickguard, as on many electro-acoustic archtop jazz guitars. The vibration of the nearby soft-magnetic strings modulates the magnetic flux linking the coil, thereby inducing an alternating current through the coil of wire. This signal is then carried to amplification or recording equipment via a cable. There may also be an internal preamplifier stage between the pickup and cable. More generally, the pickup operation can be described using the concept of a magnetic circuit. In this description, the motion of the string varies the magnetic reluctance in the circuit created by the permanent magnet.

    Pick up (music technology) - Wikipedia, the free encyclopedia
     
  6. Steelskin

    Steelskin Strat-Talker

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    thanks, so I dont know much about ac. So you cant just break a hot with a switch without grounding it right?
     
  7. Poseidon9447

    Poseidon9447 Strat-O-Master

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    I dont understand the question. What are you trying to do?
     
  8. Steelskin

    Steelskin Strat-Talker

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    pretty well breaking the hot off of a pickup
     
  9. Poseidon9447

    Poseidon9447 Strat-O-Master

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    I think what you want to do is install a kill switch. Yes you can. Tom Morello of rage against the machine has one installed and alot of people have put them in. Heres how to do it Guitar Killswitch there are a lot of examples on that site dont know if any are better then others.
     
  10. BOD2

    BOD2 Strat-O-Master

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    Well it is more like AC than it is DC but your meter would probably struggle to measure it as it's a complex wavefoem containing lots of harmonics rather than a simple "sine wave" that you would expect from an AC voltage.

    A sine wave creates a very pure simple tone at one frequency only. Your pickup will produce what is effectively lots of sine waves superimposed on each other. Furthermore, the amplitude of these sine wave will vary - they'll be higher (louder) initially then gradually reduce to zero.

    The output from a pickup is also very low in terms of the voltage.

    A pickup will produce a voltage without an amplifier attached - it's just a very low voltage.

    Are you looking to make a "kill switch" ? See below for detaila

    Alexplorer's Axe Hacks: Kill Switch
     
  11. Celeste

    Celeste Senior Stratmaster

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    If it is created or transferred by magnetics, it is AC. In the guitar, hopfully it is pure AC. In an amp, the AC rides on the DC and then gets seperated out by passing through a cap or transformer.

    When you talk AC you need to know a few things. Do you want to measure peak to peak voltage or RMS? What is the wave form? What is the frequency?

    Most meters give a bad approximation of RMS. Some do truly read RMS. If you want peak to peak, usually you would use an O-scope. Most meters have a limited bandwidth, which means if you try to measure voltage outside of the frequencies it likes it gives you a bad reading or none at all

    For a sign wave, the relationship of peak to peak and RMS is PtP= RMS times 1/2 the square root of 2. So if your voltage at your wall plug is 120V RMS the peak to peak voltage is about 169.7 volts.
     
  12. Steelskin

    Steelskin Strat-Talker

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    I want to kill the pickups separatly. like on off's for the pups. Im just experimenting, I have a diagram for this and its rigged the AC way so when you flick the switch it grounds the hot signal.


    Not quite like morelleos

    ---------/ ------- hot
    ------------------ ground

    Pretty well like this

    But after i looked at those diagrams for the killswitch, im pretty sure i have to ground any hot lead i put a switch on
     
  13. BOD2

    BOD2 Strat-O-Master

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    Yes - you want to ground the hot lead. If you just disconnect the hot lead then the signal will stop but you can also get lots of hum as well.
     
  14. Poseidon9447

    Poseidon9447 Strat-O-Master

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  15. Steelskin

    Steelskin Strat-Talker

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    I think I got it now.... I was curious about cutting the line and getting hum from it. I might try and rig it up both ways for fun

    thanks everyone!
     
  16. Carlsoti

    Carlsoti Senior Stratmaster

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    I think the line between AC and DC is blurred when it comes to guitar pick-ups. I'm not certain it can be called either.
     
  17. Offshore Angler

    Offshore Angler Senior Stratmaster

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    Well, that's some interesting stuff. First off, you can create DC just fine with magnetics. In fact all DC motors create DC current. It's called the reverse or "back" emf.

    Also, the preamp of a guitar amp has no DC bias, the only DC you will find in them is supplying power to the heater filaments in some amps, though most use AC.

    The current from guitar pickup is AC.

    Also, you do not need to ground a pickup to remove it. That all the selector switch does, it breaks the circuit. With no loop, there can be no hum, since there is no current path.

    The time we ground inputs would be on an A/B box, where we want to have no induced potential on the input to the amp not selected.
     
  18. Steelskin

    Steelskin Strat-Talker

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    hrmmmmm that is some interesting stuff. Im gonna try it both ways i think. see what comes about. I jsut got it all routed out some im ready to wire!