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Thread: Moving Coil Pickups for the Technically Curious

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    Moving Coil Pickups for the Technically Curious

    A guitar or bass with metal strings has the potential to utilize a new way to sense the vibrations from the string. Just think of a metal string as a "moving conductor" or a "wire in a magnetic field" (web search on the words within quotes for more information).

    I'll share with you what I have learned from tinkering with pickups for almost 50 years.

    A voltage can be generated when a wire is moved through a magnetic field. To see this with a quick experiment do this. Use an acoustic guitar and attach a scope probe across one string then move a cermic magnet near the string. Set the scope the a low mv range. Plunk the string and you will see an output in the 2 to 5 mv range. Just like traditional high impedance pickups with thousands of coil turns around magnets, the output of the string motion is a function of the actual motion vector at right angles to the field direction. This is defined a Lorentz Voltage.

    Lorentz Voltage is defined as E=LB dx/dt sin (/) (my poor excuse for a Greek letter) where:
    dx/dt is the velocity of the moving conductor;
    B is the strength of the magnetic field;
    L is the length of the conductor in the magnetic field; and
    (/) is the angle of the direction of conductor motion relative to the direction of the magnetic field.

    Based on the above formula and my own experiments, the voltage induced within the string increases as the length of the magnetic field is increased. I used a .5" wide by 6.5 " long by 0.125" thick rubberized magnet running under the string from the end of the fingerboard to near the bridge. By adjusting the magnet height to be closer to the string near the bridge I can balance the harmonic output. This arrangement puts a full quarter string length within the magnetic field.

    Now for the fun part. Obtain a low frequency current transformer such as a "CSE187L" for about $2.50 (single unit price) from Allied or Jameco. If you have a scope current probe you can use this also by just putting the probe around the string behind the nut and use a thick jumper wire to connect the string behind the probe and the bridge end of the same string. This now forms a single turn loop with the string acting as the ribbon in a "ribbon microphone". Use the CSE187L by attaching the primary (single turn transformer wire) to the string with jumper wires attached to the string behind the nut and behind the bridge. Attach your scope or amp to the secondary and observe or listen to the sound. The output of the CSE187L is about 21 ohms DCR and matches a low impedance XLR to high Z matching transformer 500 to 50,000 ohms at a 1:10 turns ratio very well or a microphone mixer XLR input.

    The CSE187L has a 1:500 turns ratio and is rated for a 50 to 400Hz frequency range but it goes well beyond that. You can even connect two strings in series by electrically connecting the individual machine heads of the bass E and A strings together and attach the CSE187L primary behind the bridge to these two strings and make a quick two string pickup for test purposes.

    For a little more output you can obtain a "low frequency torroid current transformer" with turns ratios up to 1: 3000. Just run a jumper from the string behind the nut, loop it through the torroid as the primary loop and connect the other end behind the bridge.

    You might ask, why has this pickup not been popular?

    1. You need to have a ground return from the strings at the nut end into the body of the guitar near the bridge.

    2. It does not just drop in with a standard single coil or humbucker footprint.

    3. The strings can act as an antenna and pickup hum.

    As another experiment take a soldering gun and use it as a hum source. When a single string or two series strings are connected to an amplifier, move the soldering gun near the string and listen to the hum.

    Here is the challenge for the technically curious.
    (1) How could you apply traditional humbucking techniques from traditional high impedance pickups to this moving coil pickup?

    (2) Using the current transformer techniques described above, how could you adjust the output level of each string to obtain a more acoustically balanced string output.

    (3) What other musical applications can be derived form having individual and isolated string outputs.

    I hope this stimulates some thinking and introduces another approach to making guitar pickups. I hope some of you try these quick experiments and share your results.

    Joseph Rogowski

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    Last edited by bbsailor; 09-03-2009 at 01:04 AM.

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    Neat Ideas! Prelim. questions...

    so if this were applicable to all six strings would there be a need for six transformers, or would it be possible to connect all strings in series?

    If all strings were connected in series to one transformer, then if you played a barre chord with six strings vibrating would the total voltage increase making chords much louder than when playing single strings?

    Would there be a problem with eddy currents with that much magnet under the strings, or would it be relative to the proximity of the tranformer(s)?

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    Quote Originally Posted by StarryNight View Post
    so if this were applicable to all six strings would there be a need for six transformers, or would it be possible to connect all strings in series?
    You could do it with six transformers to have individual string outputs. However, you could also use a single toroid and loop each string through a separate primary toroid winding, thus mixing the six strings in one transformer. On my first guitar modification with this pickup, I removed the guitar fingerboard; put a strip of copper sheeting down the neck, soldered the top of the copper sheet to a brass nut; routed the other end of the copper sheet into the body of my Applause acoustic guitar; mounted six 6 ohm to 20K transformers on the heel of the neck wrapped in copper foil for additional shielding. I used a copper rivet in each bridge hole to thread the ball of the string through; soldered a wire lead to each copper rivet that attached to that string's transformer and the common ground return from under the neck. The output from each string 20K side went to a separate pin of an 8-pin microphone connector with a common ground. Then I made a breakout cable with the 8-pin connector on one end and the broken-out leads with a 1/4" plug so I could plug the guitar into a 6-channel microphone mixer. I had individual volume, EQ, and panning of each string on the mixer. I mounted ceramic magnets on a wood bar that mounted in the sound hole like a clamp-in acoustic guitar pickup.


    Quote Originally Posted by StarryNight View Post
    If all strings were connected in series to one transformer, then if you played a barre chord with six strings vibrating would the total voltage increase making chords much louder than when playing single strings?
    Not necessarily.

    Quote Originally Posted by StarryNight View Post
    Would there be a problem with eddy currents with that much magnet under the strings, or would it be relative to the proximity of the tranformer(s)?
    The rubberized magnets have less intensity than ceramic magnets and can be installed with three .5" wide strips, one strip for two adjacent strings. Eddy currents are not a problem. The transformers are typically located behind the bridge away from the magnets.

    I hope this encourages you to give this a quick try to experiment on one string with a current-based pickup. You can try this with just two alligator clips and one 8 ohm transformer (70 volt, low wattage speaker matching transformers also work) to better match the low-Z of the string to something more useful for an amp input. Use any hand-held ceramic magnet to listen to the sound and the better upper harmonics masked by high-Z pickups.

    Joseph Rogowski

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    Quote Originally Posted by bbsailor View Post
    A guitar or bass with metal strings has the potential to utilize a new way to sense the vibrations from the string. Just think of a metal string as a "moving conductor" or a "wire in a magnetic field" (web search on the words within quotes for more information).

    I'll share with you what I have learned from tinkering with pickups for almost 50 years.

    A voltage can be generated when a wire is moved through a magnetic field. ....
    There are a number of old patents on just this. With modern rare earth magnets, it may have become practical at last.

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    Quote Originally Posted by Joe Gwinn View Post
    There are a number of old patents on just this. With modern rare earth magnets, it may have become practical at last.
    Joe,

    You are correct about early patents.

    When you try to maximize the voltage from each individual string through a separate transformer you want a transformer with 5 to 10 times the impedance of the string typically between about 0.5 ohms to about 2 ohms. The size of the core wire will primarely govern the impedance of each string with the low E string having the lowest impedance and the high E string having the highest impedance. This is sort of like matching the ribbon in a ribbon microphone. Now you have six string ribbons to balance with each string having a different center frequency and impedance range.

    However, when you try to combine the strings using a single transformer, using a current transformer (CT) approach produces a better and more economical approach. You can think of putting the CT in the common ground return leg of the circuit using one CSE187L or by using a toroid with several thousand turns and wrap a lead from each string through the toroid back to the ground return to attempt to balance the output from each string.

    With a little creative alternate phasing of adjacent strings, you can even achieve a degree of humbucking to keep the strings from acting as hum antennas. This approach opens up the economical possibilities of using a single CT costing less than $10.00.

    New methods of combining the truss rod neck strengthing/adjustment function
    with a ground return electrical function can offer some new design opportunities for building a wide bandwidth pickup.

    Putting too strong a set of magnets will dampen the strings. That is why I used the rubberized magnets over a longer length of the string for more higher harmonics. There is room for experimentation to optimize for a good, balanced sound by using various magnet configurations.

    Right now I am thinking the guitar output should be more aligned with the range of microphone output at low impedance to maintain fidelity. 500 ohm to 50,000 ohm matching transformers are cheap and you only need one at the amp end or use an outboard microphone preamp to feed the guitar amp.

    I welcome your thoughtful comments.

    Joseph Rogowski

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    ...

    I ran across that patent as well, but have no idea what number it was or if I saved it, its not a new idea. Problems that could happen is with the bass strings being fatter would generate a higher output than the treble strings, but I guess with a regular pickup they do anyway. Its a cool idea but would probably give a very hifi sound and not appeal to mass market, but then again I guess Lace sells those Alumatone things.....

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    probably tinking of these Possom.
    Attached Files Attached Files

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    Pickup Maker David Schwab's Avatar
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    Another one, but more complicated.
    Attached Files Attached Files

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    ...

    So much for new ideas, eh? Yeah those are it, though haven't seen the last one before. I think it would be a hard thing to pull off and probably wouldn't sell. Just getting good electrical contact with the strings would require special hardware and different strings would probably conduct differently maybe. Still would be interesting to hear what it sounds like...

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    Quote Originally Posted by Possum View Post
    So much for new ideas, eh? Yeah those are it, though haven't seen the last one before. I think it would be a hard thing to pull off and probably wouldn't sell. Just getting good electrical contact with the strings would require special hardware and different strings would probably conduct differently maybe. Still would be interesting to hear what it sounds like...
    Possum,

    Here is a quick 5 minute way to try this assuming you have a 4 or 8 ohm primary transformer with a 5K to 20K output. Radio Shack small 70 volt speaker transformers work well using the lowest wattage tap which gives the highest turns ratio.

    Alligator clip the low impedance side of the transformer to two adjacent strings on the guitar neck behind the nut. These two strings will go over the metal bridge (shorted together) and will be then seen by the transformer as being in series. Attach the high impedance side of the transformer to a 1/4" phone jack. Connect the jack to an amplifier with a coax guitar cable. The magnets on the traditional guitar pickups will give you some sound but it will be rather weak because the magnetic field is narrow. Take a hand-held ceramic magnet or single coil pickup and hold it or place it parallel with the strings for a longer magnetic field and you will hear the output increase. Listen to the higher harmonics.

    By moving the magnet closer to the neck it will have a more mellow sound and when moved closer to the bridge it will have a sharper sound.

    Use double stick tape to mount the magnet under a string set so you can play these two adjacent strings to listen to it while playing simple music. Put it on the two bass strings and you can fingerpick and send the bass notes to a separate amplifier. No permanent mods to your guitar are required to do this quick test.

    No special hardware is needed to make contact with the strings. Just ensure that the bridge inserts are metal and clean, and that the nut is non-conductive (for this quick test).

    I am not trying to change the pickup-maker-market but just trying to share ideas to offer more alternatives. Ultimately, the sound is in the ear of the beholder. Give it a try and listen to it. Read the patents and compare what you hear to the claims made by the inventors who mention better higher harmonics.

    Using this technique shifts the pickup-maker requrement to wind thousands of turns of very thin wire to using off-the shelf components and mechanical assemblies to package and embed these pickups inside or on the guitar. Here is where creative adaption by the pickup-make community where the minds many are much better than the worn-out mind of one.

    Joseph Rogowski

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    Quote Originally Posted by bbsailor View Post
    When you try to maximize the voltage from each individual string through a separate transformer you want a transformer with 5 to 10 times the impedance of the string typically between about 0.5 ohms to about 2 ohms. The size of the core wire will primarily govern the impedance of each string with the low E string having the lowest impedance and the high E string having the highest impedance. This is sort of like matching the ribbon in a ribbon microphone. Now you have six string ribbons to balance with each string having a different center frequency and impedance range.
    Yes.

    However, when you try to combine the strings using a single transformer, using a current transformer (CT) approach produces a better and more economical approach. You can think of putting the CT in the common ground return leg of the circuit using one CSE187L or by using a toroid with several thousand turns and wrap a lead from each string through the toroid back to the ground return to attempt to balance the output from each string.

    With a little creative alternate phasing of adjacent strings, you can even achieve a degree of humbucking to keep the strings from acting as hum antennas. This approach opens up the economical possibilities of using a single CT costing less than $10.00.

    New methods of combining the truss rod neck strengthing/adjustment function with a ground return electrical function can offer some new design opportunities for building a wide bandwidth pickup.
    All true, but I suspect that it didn't work enough better than a traditional pickup to justify the complications. That said, rare earth magnets may have tipped the balance. Or maybe not.

    Putting too strong a set of magnets will dampen the strings. That is why I used the rubberized magnets over a longer length of the string for more higher harmonics. There is room for experimentation to optimize for a good, balanced sound by using various magnet configurations.
    Actually, it isn't really (or wholly) the strength of the magnet that matters. If you have a steel string vibrating perpendicular to a strong but uniform field, there will be no wolf tones. If you do not complete the electrical circuit and short the string, there will be no damping either. If you provide a path for the voltage induced in the vibrating string is drive a current, there will be damping in proportion to the magnitude of the driven current, but no wolf tones.

    It's the non-uniformity of the field that causes wolf tones, and also causing damping. It's the side pull that varies with distance of string from the magnet that causes the problem.

    The test is a aspirin-pill sized magnet with two parallel strip-shaped mild steel polepieces. The string passes between the polepieces, where the magnetic field from the pill (also between the polepieces) is fairly uniform. The field is parallel to the pickguard, so vibration perpendicular to the pickguard will induce max voltage. This is easy to arrange on a test guitar without modifying the guitar. The magic ingredient is duct tape.

    Right now I am thinking the guitar output should be more aligned with the range of microphone output at low impedance to maintain fidelity. 500 ohm to 50,000 ohm matching transformers are cheap and you only need one at the amp end or use an outboard microphone preamp to feed the guitar amp.
    This can work. But high fidelity isn't necessarily desired.

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    About to try this!

    I have Graphtech-style (non-conductive) saddles installed in a Tune-O-Matic style bridge, and I've got hold of some polycarbonate sheeting for the tailpiece.

    My guitar looks just like this.


    My plan is to not do any permanent mods, so the fretboard is staying on and I'll be running some metal tape along the back (or front if it fits!) of the neck for string ground.

    I'll make the poly tailpiece section large enough to hold the additional electronics and controls. Right now I'm strongly leaning toward BJT common base amplifiers for each string, and actively canceling common mode hum/noise. Looking for some opinions/guidance in this area.

    It will probably take me a while to get everything together, but I'm really looking forward to this!

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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by earthtonesaudio View Post
    I have Graphtech-style (non-conductive) saddles installed in a Tune-O-Matic style bridge, and I've got hold of some polycarbonate sheeting for the tailpiece.
    Is that going to be strong enough? You might want to pick up a cheap stop tail and then drill out the holes bigger and line them with some kind of non conductive tubing.

    My plan is to not do any permanent mods, so the fretboard is staying on and I'll be running some metal tape along the back (or front if it fits!) of the neck for string ground.
    If you are doing that to ground your hand, you will then be shorting out the strings when you touch them. I wouldn't worry about the string ground.

    I'll make the poly tailpiece section large enough to hold the additional electronics and controls. Right now I'm strongly leaning toward BJT common base amplifiers for each string, and actively canceling common mode hum/noise. Looking for some opinions/guidance in this area.

    It will probably take me a while to get everything together, but I'm really looking forward to this!
    Sounds like a cool project!

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    The signal will be taken from the bridge end and the nut end needs to be grounded for there to be a complete circuit. I hadn't really thought about it before, but I think compared to the milli-ohms resistance in the strings, my body is basically an open circuit, so I'm not really worried about shorting the string signal before it makes its way to the bridge.

    I plan on using a large piece of poly to make the tailpiece (maybe sort of like a trapeze style, extending all the way to the strap button), so the forces from the anchor posts vs. the string tension will be spread over a large area.

    Another reason for using polycarbonate is that it's clear and I want to put silly lights inside.

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    I've been thinking about this and I have a technical question.

    First is, the frets are conductive. So if the ground return is the nut, won't the effective resistance be altered whenever you fret two or more strings on the same fret?

    For instance, if you played the high E string, fretted at the 12th, you have the vibrating portion of the string providing an AC signal and the stationary part of the string providing some resistance to ground. Then if you were to fret the low E at the same fret, there are now two parallel paths to ground. Would this cause the gain of the system to change?

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    I was looking at utilizing this system a year ago as I have been looking for a setup that allows for individual string outputs. I abandoned this idea when it struck me that the conductive frets would create an issue. Since then I have been thinking about how to utilize such a simple setup and have come up with several possibilities.

    1. Refret the neck to where the frets do not extend the width of the neck. The smaller frets would be only as wide as necessary for the string. It would require a separation space or a nonconductive material between itself and its neighboring fret so as not to pass the current over.

    2. Find or create a nonconductive fret material

    3. Go fretless!

    I am very interested in this chat as I have been looking for some time for the information posted here.
    Cabezon

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    Quote Originally Posted by cabezon View Post
    I was looking at utilizing this system a year ago as I have been looking for a setup that allows for individual string outputs. I abandoned this idea when it struck me that the conductive frets would create an issue. Since then I have been thinking about how to utilize such a simple setup and have come up with several possibilities.

    1. Refret the neck to where the frets do not extend the width of the neck. The smaller frets would be only as wide as necessary for the string. It would require a separation space or a nonconductive material between itself and its neighboring fret so as not to pass the current over.

    2. Find or create a nonconductive fret material

    3. Go fretless!

    I am very interested in this chat as I have been looking for some time for the information posted here.
    Cabezon
    Cabezon,

    There is no need to go to all the trouble to splitting the frets. Here is why. Consider the nut end of the string as the common ground end. Use the truss rod as the common ground return path connected to the metal nut. This way if you fret multiple strings across a fret, the hot ends of the strings are still isolated behind the bridge end of the strings and are still free to produce an independent output. The output of each string is between the common ground and each individual string isolated from touching a common metal bridge. Use nylon inserts or Graphtech bridge inserts to prevent shorting out of the strings. The best transformers to try are miniature audio output (4 or 8 ohms to 20K to 50K) used with the low impedance side connected between each string and the common ground.

    The string impedance is so low that making the strings shorter will not affect the output level.

    I hope this helps.

    Joseph Rogowski

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    Quote Originally Posted by bbsailor View Post
    The string impedance is so low that making the strings shorter will not affect the output level.

    I hope this helps.

    Joseph Rogowski
    That's just what I was looking for, thanks!

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    Alright, a new related question:

    How much hum should one expect to hear from the string output, after impedance matching and/or amplification to "normal" (compared to a standard pickup) levels?


    By the same token, what would be the most practical method of humbucking, if you wanted to keep the individual string signals separate for hexaphonic purposes?

    My first thought is to run a dummy string through the neck, and subtract it's output from each individual string's output.

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    Quote Originally Posted by earthtonesaudio View Post
    Alright, a new related question:

    How much hum should one expect to hear from the string output, after impedance matching and/or amplification to "normal" (compared to a standard pickup) levels?


    By the same token, what would be the most practical method of humbucking, if you wanted to keep the individual string signals separate for hexaphonic purposes?

    My first thought is to run a dummy string through the neck, and subtract it's output from each individual string's output.
    earthtonesaudio,

    I'm glad someone has tried this.

    Hum should be rather low because the string is effectivly grounded at one end, the nut end through the ground return. Make sure that all the following are grounded.

    1. Truss rod or ground return from the nut side of the string
    2. Transformer secondary ground connection from each string
    3. Transformer metal frame

    To humbuck, simply reverse the phase of alternate strings. Use an oscilloscope to see the phase of the input to each transformer and the outputs. Any common noise should be neutralized like in a traditional humbucker.

    Dummy String? The easiest method is to use the truss rod as the ground return or remove the fingerboard and lay a thin copper strip under the fingerboard.

    If you use two strings for one string path you do not get individual string output. You need the common ground return from the nut to get an individual hex output for midi.

    Please describe what you discovered when you tried this moving string pickup? How did you implement it? What is your output from each string?

    Here is tip. The longer the magnetic field under the string the higher the output. If you put too strong of a magnet under the string, it will damp the string vibrations. Try using the Radio Shack 1" rectangular ceramic magnets, part number 64-1879. There are 5 magnets per pack so three packs should give you a 5" long magnetic field under the strings with the 1" side of the magnets in line with the strings, or three across. Put some foam under the magnets and you can use screws in the holes in the magnets to fine tune the distance from the magnets to the strings. Position the magnets closer to the string as they get closer to the bridge to balance the upper harmonics where the string has less vibration amplitude.

    This is fun stuff and an interesting alternative to traditional pickups.

    Joseph Rogowski

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    Thanks Joe,

    I haven't actually built anything yet, but I plan on prototyping something simple (maybe just a 2x4 board with strings) to test out these ideas.

    My main concept is to use an active preamp to boost the weak signal from the strings. I figure it's going to be a lot of gain, so any common mode noise induced in the strings has to be eliminated.

    Your comments about using pairs of strings to cancel common mode noise leads me to believe that a "dummy string" buried in the neck would probably work. I guess the key would be to keep the dummy as physically close to the signal string as possible.

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    Quote Originally Posted by earthtonesaudio View Post
    Thanks Joe,

    I haven't actually built anything yet, but I plan on prototyping something simple (maybe just a 2x4 board with strings) to test out these ideas.

    My main concept is to use an active preamp to boost the weak signal from the strings. I figure it's going to be a lot of gain, so any common mode noise induced in the strings has to be eliminated.

    Your comments about using pairs of strings to cancel common mode noise leads me to believe that a "dummy string" buried in the neck would probably work. I guess the key would be to keep the dummy as physically close to the signal string as possible.
    earthtonesaudio,

    The so called "dummy string" is actually the ground return. What you want is a very low resistance return path so that the signal feeding the passive input transformer (3.2 ohms to 20K ohms impedance) without the noise of active circuits. Try measuring the impedance of each guitar string with the Exech LCR meter. You want the return path to be about 10 times lower in resistance than the lowest resistance string which is at about 0.5 ohms.

    The fun comes in when placing magnets under the strings to emphasize different harmonics.

    Joseph Rogowski

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    Yes, I was imagining using a low-resistance path (truss rod, aluminum beam, etc.) as the ground return for all strings, and separate, 1-per-string "dummy strings" solely for noise rejection.

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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by earthtonesaudio View Post
    and separate, 1-per-string "dummy strings" solely for noise rejection.
    I don't think it works that way. On a pickup with a coil, the coils are wired in reverse and each has an opposite magnetic polarity. Whereas the string has a resistance and will get current flowing when in a magnetic field, it's not going to buck hum with another string unless you are presenting an opposite polarity for the common mode noise.

    Now if you had the strings in some kind of pairs with opposite magnetic polarity, or at least wired into the transformer, that would work.

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    I was thinking something like this (see attached drawing).

    The signal and dummy strings connect together at the nut end of the guitar, along with the ground return. The signals are taken at the bridge end of the guitar. The dummy string runs parallel to the signal string, buried in the fretboard or somewhere close like that.

    The dummy string doesn't move, so the magnetic field does not affect it at all. It picks up pretty much the same environmental noise as the signal string, and the differential amplifier cancels the noise while providing voltage gain and line driving ability.


    The ground return has to traverse the length of the neck, so in order to have comparatively low resistance and inductance, it would have to be a thicker "wire," possibly like a truss rod or metal reinforcement beam.
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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by earthtonesaudio View Post
    The dummy string doesn't move, so the magnetic field does not affect it at all.
    It will effect it if there is a moving string carrying current over it. Pickup coils don't move either.

    Look up these patents by Clevinger:

    4408513

    4499809

    They are something similar
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    It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. Albert Einstein


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    Quote Originally Posted by David Schwab View Post
    It will effect it if there is a moving string carrying current over it. Pickup coils don't move either.
    Hm. I think you're right.

    But I imagine it must be a small effect, if the strings are a fretboard's thickness apart. This geometry can't possibly make for a very good transformer.

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    Noodle of Reality Steve Conner's Avatar
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    I don't see the point of any of these dummy strings. All that matters is the loop area formed by the strings and the ground return, the system will pick up magnetic hum in proportion to that area. The impedance is so low that it shouldn't pick up electrostatic interference at all, provided of course that you ground one point of the loop, which you should.

    I think Mr. Rogowski recommended reversing the polarity of some of the strings and also reversing the magnets on those strings. If you can get equal loop areas that contribute to the output in opposite polarities, you've got a humbucker. You may not even need to reverse the magnets: does the phase of one string relative to another matter?

    If you connected the odd-numbered strings in parallel to the non-inverting input of a diff amp, and the even-numbered ones likewise to the inverting input, that's probably about as good as the humbucking would get, though at the cost of losing individual string outputs.

    I'm not sure if a ground return down the neck would even be needed in this case, as long as the strings are all connected by a brass nut or the like. Electrostatic interference would hit the diff amp's inputs in phase and be cancelled.

    Then again, a copper fingerboard with ceramic frets, wouldn't that look neat?

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    Last edited by Steve Conner; 03-25-2010 at 11:39 AM.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Quote Originally Posted by earthtonesaudio View Post
    The dummy string doesn't move, so the magnetic field does not affect it at all. It picks up pretty much the same environmental noise as the signal string, and the differential amplifier cancels the noise while providing voltage gain and line driving ability.
    As drawn, IC1 is not a differential amplifier. If you change the IC1 circuit to be a true differential amplifier, humbucking could be achieved.

    However, you also need to design to tolerate a static electricity discharge to either input of IC1, or the circuit will not survive the first dry day.

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    Noodle of Reality Steve Conner's Avatar
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    Oh, yeah good point... I forgot about ESD, we haven't had a dry day in Scotland since before ICs were invented.

    I prefer the passive idea with the step-up transformers myself. What if you connected the strings all together at the nut, then at the bridge: connect all the odd strings to point A, all the even strings to point B, and then hook the step-up transformer between points A and B?

    You could ground the system at A or B, or the nut, it makes no difference that I can see.

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    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    It's always refreshing to see new approaches to an old idea. It proves that most technically-oriented people are always thinking.

    The downside to all of this is that many musicians, and not just guitarists, are hardcore traditionalists and things like this don't fly. I saw a prototype system similar to this a LONG time ago, where the strings, which were magnetized ala the early Rickenbacker horseshoe magnet system, went through small circular coils near the bridge, which were fed to opamps. Then there was a guitar that I THINK was called the Lightwave, using infrared LED's and optocoupler's to read string vibration. Both were touted as revolutionary, both died before production commenced. Even the Gibson Robot has flatlined.

    The problem is that musicians always SAY that they are open-minded and want something different, when in fact, they just want better versions of the old stuff. Go figure!

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    John R. Frondelli
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    Noodle of Reality Steve Conner's Avatar
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    Totally, I mean we're still using vacuum tubes, for goodness' sake!

    I need an EMI-proof guitar for my Tesla coil guitar act, so the Lightwave thing would have been great.

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    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    I think you need the step up transformers in order to get good enough signal to noise ratio (over preamp noise). Also this has the advantage of providing the possibility of a differential input if you need it.

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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by jrfrond View Post
    Then there was a guitar that I THINK was called the Lightwave, using infrared LED's and optocoupler's to read string vibration. Both were touted as revolutionary, both died before production commenced.
    Lightwave is still in business!

    LightWave System Pickup

    Then of course there was the Hoag optical pickup. He was the first.

    HOAG OPTICALGUITARS SITE

    Roland did this string as coil idea in reverse with their first guitar synth the GR-500. It had a large magnet under the strings by the neck and it ran the output of each string back to the actual string. That created infinite sustain.

    I always thought this was really exciting stuff. This got me into messing with optical pickups and hall effect sensors back in the 70's. I should try that stuff again.
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    Quote Originally Posted by jrfrond View Post
    It's always refreshing to see new approaches to an old idea. It proves that most technically-oriented people are always thinking.

    The downside to all of this is that many musicians, and not just guitarists, are hardcore traditionalists and things like this don't fly. I saw a prototype system similar to this a LONG time ago, where the strings, which were magnetized ala the early Rickenbacker horseshoe magnet system, went through small circular coils near the bridge, which were fed to opamps. Then there was a guitar that I THINK was called the Lightwave, using infrared LED's and optocoupler's to read string vibration. Both were touted as revolutionary, both died before production commenced. Even the Gibson Robot has flatlined.

    The problem is that musicians always SAY that they are open-minded and want something different, when in fact, they just want better versions of the old stuff. Go figure!

    John,

    The purpose of starting this thread was to offer another perspective on building a string transducer. This may not take over the world like traditional replacement pickups have done when they easily fit a standard pickup humbucker, single coil, or P90 footprint. However, this new technique offers technical guitar people a way to easily experiment with using technologies that were common in the early days of radio and ribbon microphones but with each string functioning as an individual and isloated ribbon or as part of a collective set of ribbons. This thread simply explains how approaches different from thousands of turns of very fine wires around a magnet can also produce sound and provide individual, isolated string outputs for those who might want to use that characteristic.

    Add to this the advent of digital signal processing, midi, hex pickups where there is an interest in saying; what if i can use the signal induced on a moving string in a magnetic field? Then, what happens is a discussion like has evolved in this thread.

    The ear is the final arbitrator in what sounds good, Science attempts to explain what people seem to like and also tries to replicate it. Knowledge gives guitar builders and techies additional alternatives.

    Joseph Rogowski

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