String based current induced pickup shared idea

[bbsailor]

I have been tinkering with guitars and pickups for many years. One day I was looking at how ribbon microphones work and saw that the ribbon acts as both the mic diaphragm as well as part or a very low impedance input circuit.
Then I thought how might a guitar string be similar to to ribbon in the mic? I used small audio transformer rated a 8 Ohms to 10K ohms. The turns ratio is calculates by dividing the primary into the secondary with 10,000 by 8 being 1250, then take the square root of 1250 being 35.35. Whatever voltage is induced in the vibrating string with a magnet below the string is boosted by the transformer turns ratio. A 1 mv string induced signal would come out of the transformer as about 35 mv according to theory. Practical matching concepts for such a low input impedance as a string resistance requires these considerations.
1. Reduce the resistance of the connection between the string ends and the transformer input connections to reduce resistive losses.
2. The length of the magnet under the string with longer magnetic fields under the string creating a higher output.
3. How to integrate the above constraints into a guitar design.

1. Use a copper nut with a low resistance connection to the neck truss rod to act as a common ground return to bring the nut end of all the strings inside the guitar body near the bridge where the hot end of each string gets connected to an individual transformer with the lowest resistance to minimize resistive input signal losses.

2. When experimenting with this concept, alligator clip the 8 ohm side of the transformer across the same metal string behind the nut and behind the bridge. I used a .25 inch wide by 2 inch long magnet across all the strings and listened to the output. Then, I turned the magnet to go lengthwise under the one string that was connected to the transformer and the output level was louder.

3. The implementation of this pickup concept is not as simple as just installing a pickup as a separate device but requires a guitar builder to use the neck truss rod as a low resistance string end ground to return to the guitar body with the string ends being behind the bridge as being the individual inputs to each 8 ohm side of the six transformers. The six transformers can be wired in series with a small pot with a screwdriver activation to adjust the level of each string individually and passively.

Once I got my prototype working, I wired the hot output from each transformer located near the bridge to a 8 pin connector with one pin being the common ground and six other pins for the hot connection from each string. Then I made a breakout cable using the 8 pin matching connection to the guitar 8 pin connection mounted on the guitar body with 6 conductor shielded cable and each strand attached to a breakout connection with 6 quarter inch plugs that I could plug into a 6 channel mixer to adjust the volume and tone of each individual string. This really works!

This idea is not good for pickup makers but is a good concept for those who make both guitars and pickups as it requires modifying the truss rod to become a ground return to bring a low resistance connecting back inside the guitar body where the six individual string transformers are located and then reach out to the individual string outputs going to a six channel mixer.

I hope this gives some guitar builders or some pickup tinkerers something to try to get another perspective on how pickups work or might evolve to in the future.

Joseph J. Rogowski

[Mike Sulzer]

I have been tinkering with guitars and pickups for many years. One day I was looking at how ribbon microphones work and saw that the ribbon acts as both the mic diaphragm as well as part or a very low impedance input circuit.
Then I thought how might a guitar string be similar to to ribbon in the mic? I used small audio transformer rated a 8 Ohms to 10K ohms. The turns ratio is calculates by dividing the primary into the secondary with 10,000 by 8 being 1250, then take the square root of 1250 being 35.35. Whatever voltage is induced in the vibrating string with a magnet below the string is boosted by the transformer turns ratio. A 1 mv string induced signal would come out of the transformer as about 35 mv according to theory. Practical matching concepts for such a low input impedance as a string resistance requires these considerations.
1. Reduce the resistance of the connection between the string ends and the transformer input connections to reduce resistive losses.
2. The length of the magnet under the string with longer magnetic fields under the string creating a higher output.
3. How to integrate the above constraints into a guitar design.

1. Use a copper nut with a low resistance connection to the neck truss rod to act as a common ground return to bring the nut end of all the strings inside the guitar body near the bridge where the hot end of each string gets connected to an individual transformer with the lowest resistance to minimize resistive input signal losses.

2. When experimenting with this concept, alligator clip the 8 ohm side of the transformer across the same metal string behind the nut and behind the bridge. I used a .25 inch wide by 2 inch long magnet across all the strings and listened to the output. Then, I turned the magnet to go lengthwise under the one string that was connected to the transformer and the output level was louder.

3. The implementation of this pickup concept is not as simple as just installing a pickup as a separate device but requires a guitar builder to use the neck truss rod as a low resistance string end ground to return to the guitar body with the string ends being behind the bridge as being the individual inputs to each 8 ohm side of the six transformers. The six transformers can be wired in series with a small pot with a screwdriver activation to adjust the level of each string individually and passively.

Once I got my prototype working, I wired the hot output from each transformer located near the bridge to a 8 pin connector with one pin being the common ground and six other pins for the hot connection from each string. Then I made a breakout cable using the 8 pin matching connection to the guitar 8 pin connection mounted on the guitar body with 6 conductor shielded cable and each strand attached to a breakout connection with 6 quarter inch plugs that I could plug into a 6 channel mixer to adjust the volume and tone of each individual string. This really works!

This idea is not good for pickup makers but is a good concept for those who make both guitars and pickups as it requires modifying the truss rod to become a ground return to bring a low resistance connecting back inside the guitar body where the six individual string transformers are located and then reach out to the individual string outputs going to a six channel mixer.

I hope this gives some guitar builders or some pickup tinkerers something to try to get another perspective on how pickups work or might evolve to in the future.

Joseph J. Rogowski

I guess this should work with any conductive string that is not necessarily magnetic. So you could make strings out of certain stainless steels: less corrosion. Also you would have no string pull, so you could make the magnets stronger than practical with magnetic strings to increase the output.

So you get an eight input recording interface and you can record each string separately and construct the sound of the instrument after the fact any way you want. Yes, you can do that with six coil magnetic pickups, but I am thinking that this gives a very neutral sound that can be manipulated with ease and flexibility.

[bbsailor]

Mike,

I am glad you know the benefits of minimizing string pull. Based on my research, the string resistance and wire resistance to attach to the low impedance side of the transformer should work like this. The wire resistance should be about one tenth the string resistance. The total input resistance should be about one tenth of the transformer input impedance to minimize matching losses.

Any of these audio transformers will work: 8 ohms to 10K ohms, 8 ohms to 15K ohms and 8 ohms to 20K ohms. Higher turns ratios provide more output. Here is where the ear helps select the best tone range. Laying magnets along the string bottoms from the end of the neck back to the bridge may put about a quarter of the string length within a magnetic field. Here is where some experimentation with the magnetic length and strength will offer some tonal variations besides the ability to adjust each string level electronically. Maybe even a single magnet 2.25 inches wide by 6 inches long by .25 inches thick could be mounted on some foam to adjust the magnet angle to get closer to the strings near the bridge.

It would be nice to see if any MEF members try this out and post their results, questions and potential improvements.

Thanks

Joseph J. Rogowski

[Antigua]

Does the sound change depending on where the magnet is located?

If you don't care about having string to string balance, you can have some of the strings be sends and others be ground returns, with an electrical connection between the tuners. Is there much demand for string to string volume adjustment? From an economic standpoint if it could be made cheaper without string to string volume adjustment, more customers would probably opt for that.

With some low voltage high current applications I've noticed the string has to be extremely thick and often extremely short. Would a size 9 high e string for sure be thick and short enough to support enough current?

[bbsailor]

Does the sound change depending on where the magnet is located?

If you don't care about having string to string balance, you can have some of the strings be sends and others be ground returns, with an electrical connection between the tuners. Is there much demand for string to string volume adjustment? From an economic standpoint if it could be made cheaper without string to string volume adjustment, more customers would probably opt for that.

With some low voltage high current applications I've noticed the string has to be extremely thick and often extremely short. Would a size 9 high e string for sure be thick and short enough to support enough current?

Antigua, and all experimenters

The easiest way to experiment with this new pickup method is to obtain one miniature audio output transformer with an 8 ohm to 10K or up to 20K ohm rating. Solder a long piece of stranded hook up wire to attach behind the nut and a shorter piece to attach to the same string behind the bridge. Just make sure that other strings are not shorting out the test string by being electrically connected on the tuners, bridge or tailpiece. Attach the high impedance transformer output to an amp input and hand hold a variety of magnets along the string and listen to the tonal changes with the magnet in different locations along the string and then different magnet lengths.

Look up the history of ribbon microphone development and evolution to see how this induction method treats the mic aluminum ribbon as both the primary single turn coil being the current conductor as well as the vibrating diaphragm placed in between a very strong magnetic field. The very high turns ratio of the ribbon mic transformer acts more like a current transformer. To maximize the current being developed in the vibrating ribbon the transformer was located very close to the ribbon to minimize any resistive losses between the ribbon and the transformer input. Higher input current produces more output voltage thus low resistance connections are critical.

You electrically short two side by side strings together behind the nut and then isolate the tail ends of those strings from a metal bridge and tailpiece to connect the two strings to the transformer and get a signal for two strings on that single transformer but not as loud as a single string attached to the transformer.

Some other experiments you can do relate to optimizing the output by wiring two 8 ohm transformer sides to the same string in parallel and then wiring the transformers outputs in series to boost the output level.

If you have a guitar with a tune-a-matic bridge with metal string slides you can order nonmetallic slides to keep the strings isolated as long as you keep them isolated on the tailpiece where you can mount the transformers for each string as long as you have a good low resistance return connection from a metal guitar nut at the common ground nut end of the strings.

Experimenting with things you like is a very good way to gain new insights to discover new useful things to build.

Thanks

Joseph J. Rogowski

[Antigua]

I'm surprised to hear this works. I would have guessed that a guitar string is not similar enough to the ribbon mic.

So if you put the magnet over the "neck" pickup spot, does it sound at all like a neck pickup, or is the variation in sound resulting from magnetic pull on the guitar string?

What type of magnet are you using, ceramic, neo?

[bbsailor]

I'm surprised to hear this works. I would have guessed that a guitar string is not similar enough to the ribbon mic.

So if you put the magnet over the "neck" pickup spot, does it sound at all like a neck pickup, or is the variation in sound resulting from magnetic pull on the guitar string?

What type of magnet are you using, ceramic, neo?

Antigua,

Guitar strings are similar enough to ribbons in a mic that the strings do not need to be magnetic metal as is required when the string vibrates over a magnet with a coil wrapped around the magnet in a traditional pickup. When the conductive string is moving within a magnetic field the string does not need to be magnetic but only conductive.

Try this experiment. Remove a magnetic guitar string and replace it with a piece of solid copper wire. Tune it high enough to not snap but just to vibrate with the transformer attached across it behind the nut and the bridge. This temporary copper string will not stimulate a traditional guitar pickup but it will stimulate the copper string representing an non magnetic string vibrating close to a magnetic field.

This means that putting the magnet close to a non magnetic guitar string will not damp the string as if it were magnetic. If you put a .25 inch wide by 1 inch long magnet under the test string near the neck it will sound more like a traditional neck pickup than if it were moved back closer to the bridge where it would sound more like the bridge pickup. The magnet would need to be closer to the string as it gets closer to the bridge due to the string movement being less nearer the bridge.

Everyones ear is subjective as to describing what the output sounds like. This is why experimenting with this new concept will allow output measurements and aural sounds to define what sounds pleasant, good, or better than some alternatives.

Any type magnets will work, with stronger and longer magnets producing more output.

Thanks

Joseph J. Rogowski

[Antigua]

Everyones ear is subjective as to describing what the output sounds like. This is why experimenting with this new concept will allow output measurements and aural sounds to define what sounds pleasant, good, or better than some alternatives.

The harmonic content at a given location along the string is not subjective, so in asking if it sounds like a neck pickup, I mean is the location of the magnet functionally equivalent to having placed a regular pickup. If the answer is yes, then to get the sound of different pickup placements, maybe you could just position magnets in various places, which would be pretty remarkable, functionality wise. There is EQ modelling that can approximate the response curve of a high impedance pickup, but no way to approximate multiple pickup placements on the fly, until now, potentially.

One thing you mentioned was using a very long magnet. In pickup theory, if you were to have a pickup that was several inches wide, it should lack treble because the harmonics that are smaller than the width of the magnet/pickup should be self-cancelling, so one wonders if that's an issue here.

[bbsailor]

The harmonic content at a given location along the string is not subjective, so in asking if it sounds like a neck pickup, I mean is the location of the magnet functionally equivalent to having placed a regular pickup. If the answer is yes, then to get the sound of different pickup placements, maybe you could just position magnets in various places, which would be pretty remarkable, functionality wise. There is EQ modelling that can approximate the response curve of a high impedance pickup, but no way to approximate multiple pickup placements on the fly, until now, potentially.

One thing you mentioned was using a very long magnet. In pickup theory, if you were to have a pickup that was several inches wide, it should lack treble because the harmonics that are smaller than the width of the magnet/pickup should be self-cancelling, so one wonders if that's an issue here.

Antigua,

If you measure the induced voltage across the string using a scope to see the peak to peak voltage level, you will see a voltage level between 1mv and about 3mv. The output will be based on the strength of the magnet under the string, as well as the magnet placement between the end of the neck back to the bridge with the final output being raised by the transformer turns ratio to a range between about 50 mv to about 100 mv. Using different magnet lengths such as .25 inch up to 1 inch will change the output level as well as tonal changes as the magnet is moved closer to the bridge. Once you set up a test guitar, you can listen to the harmonic content with different length magnets as well as different locations under the strings. Try active buffering of each string output on the guitar to minimize any cable capacitance from rolling off the top end of the harmonics.

Joseph J. Rogowski

[Helmholtz]

Faraday's law of induction states that a voltage (EMF) is induced in a conductor loop when the total magnetic flux through the loop changes.
Total flux through the loop is given by perpendicular flux densisty (B) times loop area A.
One way to vary the flux through the loop is to make the area of the loop change, while keeping the flux density (B) constant.

The conductor loop of a ribbon mic consists of the ribbon + its terminal wires. The ribbon is placed between the poles of 2 permanent magnets and the magnetic field lines are perpendicular to plane of the loop.

Vibrations of the ribbon modulate the loop area and thus a signal voltage is generated.

[bbsailor]

Faraday's law of induction states that a voltage (EMF) is induced in a conductor loop when the total magnetic flux through the loop changes.
One way to vary the flux through the loop is to make the area of the loop change, while keeping the flux density (B) constant.

The conductor loop of a ribbon mic consists of the ribbon + its terminal wires. The ribbon is placed between the poles of 2 permanent magnets and the magnetic field lines are perpendicular to plane of the loop.

Vibrations of the ribbon modulate the loop area and thus a signal voltage is generated.

Helmholtz,

When I first did this experiment I just used thin common 18 inch long alligator clip wires to quickly attach to the 8 ohm side of the transformer across the string behind the nut and bridge. I was surprised to get a signal on the high impedance side of the transformer. Then when I looked up ribbon mic evolution I saw how the optimum design minimizes the resistive connection between the ribbon and the transformer input. Then I placed my scope across the 18 inch alligator clip wires and saw a signal due to the wire resistance being too high. Then when I used a thicker wire, one tenth the string resistance, that loss was minimized and the output from the transformer increased.

Since this guitar pickup method is so unusual, I thought I would share what I have learned with forum members so they can quickly do their own experiments and have the best initial results. The ribbon microphone is the closest technology I could find that comes close to making each string function like the ribbon when placed in a magnetic field.

Thanks

Joseph J. Rogowski

[Helmholtz]

When you short the ends of the loop, the EMF will drive a current. This current causes voltage drops across any resistance.

BTW, I expect the steel strings to show some skin effect because of the high µ of maybe 100, which lowers the skin depth.

[bbsailor]

When you short the ends of the loop, the EMF will drive a current. This current causes voltage drops across any resistance.

BTW, I expect the steel strings to show some skin effect because of the high µ of maybe 100, which lowers the skin depth.

Helmholtz,

In this situation using steel magnetic strings are not required and even would be a benefit as magnetic damping using steel magnetic strings with longer and stronger magnets under the strings would damp the vibration sustain.

The key factor is that the strings are conductive with minimal wiring losses between the string ends and the transformer input. This is an area where some new research needs to be done to optimize the output from each string due to its resistance, frequency range, restive input losses, upper harmonics desired response and magnet placement. Since the low and high frequency requirement changes with each string, you would have some creative ways to optimize one frequency range for each string unlike a single ribbon needing to match the full audio range.

Set up a quick test using one string and let us know what you find?

Thanks

Joseph J. Rogowski

[Mike Sulzer]

I think the easiest way to understand how it works is to look here: http://hyperphysics.phy-astr.gsu.edu...c/genwir2.html (voltage generated in a moving wire)

[Helmholtz]

I think the easiest way to understand how it works is to look here: http://hyperphysics.phy-astr.gsu.edu...c/genwir2.html (voltage generated in a moving wire)

Yes, that's a simplification of the general principle I explained above.
It holds if the active length of a straight wire (L) moves in a uniform B-field and B=0 for the rest of the wire/conductor loop.

In that case it holds that vL = dA/dt = rate of change of active (contributing) loop area.