Low Impedance Pickup Research

[Singer15]

LoZ pots and caps

I would try a 2.2k audio taper pot and whatever capacitance that suit your needs.

Yes indeed this works. I found a 5k pot for the tone and with that a 2uF cap seems to work just fine. Using a 2.5k for volume, which works very well. I switched off the 48v phantom power too, and that did away with the noisy pots. Now the interesting part is how this all comes together when playing through the amp in a band. I find that the pickup is very good for soloing, although it is almost too bright at times. For rhythm it seems like it lacks the lower end punch of a hiZ pickup, but that is not a bad thing. To compensate I can just turn up the volume to where the low end is loud enough to be heard in the mix. In a low volume setting it really excels, as the full tonal range of the guitar can really be appreciated. This just confirms my opinion that if you just want to make a lot of noise, stick with a humbucker, since no one can tell the difference anyway.

[Singer15]

Weird sounds from pickup

Since there is not much going on here for a while I thought I would add some more results of my experiments with loZ pickups. I made a number of these following the guidelines suggested, i.e. 36 ga wire around a neod magnet, from 500 to 750 turns. This worked well enough on a few guitars that have acoustic strings, like bronze wound and also copper wound (aka gypsy jazz strings with silver plated copper). The one problem with all of these strings is the unbalanced response - the 1 &2 strings are much louder than the rest. However, it all fell apart when I switched one guitar to flat wound steel strings. Then I encountered a horrible proximity effect that actually made the sound of the strings some other frequency entirely from what their natural one was. This was pretty strange! The pickup also started inducing weird feedback just by its own vibrations, since it was cantilevered from the pick guard. I tried sticking the pickup to the top of the guitar with putty but it still made atonal noises. I had to move the pickup back from the end of the fingerboard in order to alleviate this effect. I have tried using other weaker magnets, but they did not give enough output, so I considered them a failure. I have also found that now that I moved the pickup towards the bridge, it no longer gets even signal from the outer strings. The magnet is 50mm wide but the strings are wider. I would like to try some with slightly longer magnets which are also a bit weaker. Any suggestions?

[bbsailor]

Since there is not much going on here for a while I thought I would add some more results of my experiments with loZ pickups. I made a number of these following the guidelines suggested, i.e. 36 ga wire around a neod magnet, from 500 to 750 turns. This worked well enough on a few guitars that have acoustic strings, like bronze wound and also copper wound (aka gypsy jazz strings with silver plated copper). The one problem with all of these strings is the unbalanced response - the 1 &2 strings are much louder than the rest. However, it all fell apart when I switched one guitar to flat wound steel strings. Then I encountered a horrible proximity effect that actually made the sound of the strings some other frequency entirely from what their natural one was. This was pretty strange! The pickup also started inducing weird feedback just by its own vibrations, since it was cantilevered from the pick guard. I tried sticking the pickup to the top of the guitar with putty but it still made atonal noises. I had to move the pickup back from the end of the fingerboard in order to alleviate this effect. I have tried using other weaker magnets, but they did not give enough output, so I considered them a failure. I have also found that now that I moved the pickup towards the bridge, it no longer gets even signal from the outer strings. The magnet is 50mm wide but the strings are wider. I would like to try some with slightly longer magnets which are also a bit weaker. Any suggestions?

Singer15 and others interested,

You ran into the classic problem of neod magnets being too strong under thicker wound strings with magnetic outer winds. Most acoustic strings only have their solid magnetic core which is typically half the OD of the string. Placing this type of pickup near the end of the fingerboard puts a lot of magnetic leverage against the vibrating string and either dampens the length of the string vibration or alters the response of the string sound that you experienced.

Your magnet length needs to be slightly wider that the string width. I like to use a single magnet that is 2.25 inches wide to ensure that the end strings have at least .125 inches of magnet on the outside of them. This ensures full magnetic strength on the outside strings behaving as well as the inner strings.

Go to the K&J Magnetics web site and look up their .25 inch diameter by .125 inch tall, epoxy coated disc magnet N42 with part number of D42E. Space them to fit directly below each sting using a rigid plastic old credit card plastic as the two parallel flats to hold the wire. As an alternative try this. Place 7 magnets in line with the space between the magnets being directly under the strings. This will minimize the string pull but because of the string location related to the close magnetic fields are next to but under each string. This setup will emphasize the second harmonic which might sound better on an acoustic guitar needing to sound less like an electric guitar. I prefer epoxy coated magnets to metal coated magnets to minimize eddy currents being developed in the metal covered neod magnets and affecting the sound.

Tinkering is one of the best ways to learn new things. That is the process of how I created and supported this thread.

Have a new idea.
Tinker with building it a few different ways.
Take measurements of each variation.
Take a lot of notes.
Listen to each variation.
Research related theory.
Compare the theory with your results.
Share the results with those who are also interested.

This is what I did on this forum.

Joseph J. Rogowski

[Singer15]

bbsailor,
Thanks for the quick reply. I am curious as to how it is that a pickup made with round magnets that are touching, and hence have alternating polarity, will have a good signal? I am also curious as to where to get a longer magnet, 2.25 inches as you note. I can't find anything like that at K&J. They are all 2" or 3" long. Experimenting with another guitar that has flat wound steel strings I have found that indeed if the pickup is too close to the low E then you get the weirdness happening. Increasing the space helps greatly, and eventually the effect disappears.

[bbsailor]

bbsailor,
Thanks for the quick reply. I am curious as to how it is that a pickup made with round magnets that are touching, and hence have alternating polarity, will have a good signal? I am also curious as to where to get a longer magnet, 2.25 inches as you note. I can't find anything like that at K&J. They are all 2" or 3" long. Experimenting with another guitar that has flat wound steel strings I have found that indeed if the pickup is too close to the low E then you get the weirdness happening. Increasing the space helps greatly, and eventually the effect disappears.

Singer15,

The .25 inch round magnets are spaced about .125 inch apart with the same poles facing up, with the strings directly above the magnets. As an experimental alternative try using 7 magnets but this time space the magnets so the strings are located over the space between two magnets. Here is a crude illustration of what I mean using the i for the string and the o for the magnets.

oioioioioioio


As an experiment, listen to the sound change as you slide your pickup sideways with the magnet directly below each string and then when the string is located in the space between two magnets.


Contact K&J Magnetics and ask them if they can supply you with your desired length. I ordered a custom magnet with an epoxy coating 2.25 inches long by .375 inches wide by .25 inches high with a groove along the length on both .25 inch sides to accommodate an AWG 10 solid wire for my current transformer-based pickups.

Joseph J. Rogowski

[nickceulemans]

Hi bbsailor,
Hi everybody,

For years I am trying to make my own pickup design based on this thread. However as I am a designer and not an engineer I lack the knowledge to actually know what I am doing... Therefor I am calling upon all you guys to maybe help me out? Attached are some photographs of the prototype I made so far. The idea is to start with an aluminum T-profile and turning it into a humbucking double loop. My idea was to wrap small coils on both of the "legs". I tried it with one coil last night and got no sound what so ever. But, this could very well be because I have no tools to attach the ultra thin wire to my output jack... Am I missing something? Or should this design work in principle?

Thank you very much for all the great inspiration.
Nick
https://share.icloud.com/photos/0bt0...QRY-5evl-guHaw

[Helmholtz]

How are the magnets oriented?
To verify if your wire makes contact to the output jack, measure DC resistance.
How many turns of wire (what gauge?) does the coil have.

Is the aluminum bar going through the coil continuous or interrupted?

[nickceulemans]

How are the magnets oriented?
To verify if your wire makes contact to the output jack, measure DC resistance.
How many turns of wire (what gauge?) does the coil have.

Is the aluminum bar going through the coil continuous or interrupted?

Hi Helmholtz,

Thank you for the fast reply! I'll try to find my multimeter somewhere tomorrow for the DC resistance check. As for this test I simply hand wound the wire around the continuous aluminum "leg", so can't say the exact number of turns this time around... (I have an idea how to build a jig to wind it in the future with a counter, but I wanted to go step by step) I would expect a couple of hunderd turns?
The wire is 0.056mm solderable enamelled copper wire. The aluminum center is about 4x4mm wrapped with a plastic bobbin. The design is especially centered around creating a continuous loop of aluminum without any joints...

Thanks, Nick

Nick

[nickceulemans]

Forgot to mention that the magnets are oriented one row North facing up, the other row North facing down.

[Helmholtz]

The design is especially centered around creating a continuous loop of aluminum without any joints...

Good, that's essential as you want current running through the aluminum leg in the coil. Kudos for this design!

A couple of hunded turns will allow only for a few mV output, maybe 50 times lower than a strat PU. So you need to plug into a high sensitivity microphone input.

What about magnet polarities? The 2 rows need to have opposite poles.

EDit: Just saw you already answered and have it correct.

I have some more comments, but first you should confirm DC continuityand hopefully get some sound.

[nickceulemans]

A couple of hunded turns will allow only for a few mV output, maybe 50 times lower than a strat PU.

What I'll do tomorrow is make a new coil twice as wide and try to add as much turns on it as possible for now. As this seems to be crucial. My original idea was to add a similar coil on each leg and experiment with series/parallel/blending... In any case I'll try to count the turns as my hope is to end up with a plug and play pickup solution and from what I can read somewhere in this thread that could mean I am looking at 5.000 to 10.000 turns for each coil(?) I wonder though how e.g. Lace manages to put that many turns in such a small package.


I'll give an update asap.
Nick

[Helmholtz]

Why don't you first make sure that your wire ends are properly connected and see if you can get at least a little sound? What amp do you use?

BBsailor might know a suitable step-up transformer.

Do you have some machine/mechanism that turns the bobbin on the aluminum leg for winding?

[Helmholtz]

I must have been blind (or too tired) last night so I missed the main problem of this construction:

As electrical conductors crossing at right angles don't magnetically couple, the transformer principle won't work if the aluminum loop runs through the center of the coil. Good coupling is necessary for efficient signal transfer from the sensing loop to the coil.

The primary loop (alu) should run through the window of a ferromagnetic core (which also carries the coil) and not through the center of the (secondary) coil.
In an Alumitone the transformer core is assembled around the aluminum leg.

As it won't be easy to find miniature laminations that allow this kind of assembly, you may try to make your own (toroidal) core from a plain guitar string:
Feed as many turns of the string as possible through the center of your coil (filling the hole completely) and around the aluminum leg to produce a tight toroid. This won't be a perfect solution but should allow for some coupling and signal output.
Better results should be obtained if the core is wound from a thin stripe of mu-metal foil instead of the string.

[bbsailor]

Hi bbsailor,
Hi everybody,

For years I am trying to make my own pickup design based on this thread. However as I am a designer and not an engineer I lack the knowledge to actually know what I am doing... Therefor I am calling upon all you guys to maybe help me out? Attached are some photographs of the prototype I made so far. The idea is to start with an aluminum T-profile and turning it into a humbucking double loop. My idea was to wrap small coils on both of the "legs". I tried it with one coil last night and got no sound what so ever. But, this could very well be because I have no tools to attach the ultra thin wire to my output jack... Am I missing something? Or should this design work in principle?

Thank you very much for all the great inspiration.
Nick
https://share.icloud.com/photos/0bt0...QRY-5evl-guHaw

nick,

All pickups benefit from physical design or appearance but must behave according to the laws of physics or in this case electromagnetic induction. Typical guitar pickups are simply voltage generators by winding many thousand turns of very fine (AWG 42 or 43) hair thin wire around a magnet with the ferrous guitar strings being magnetized by the magnet below them and then vibrating this moving the magnetic field through all those turns of very fine wire to generate a voltage designed to feed the high impedance of a guitar amp input impedance, typically about 1 meg ohm. When you add the parallel resistance of the volume pot of 500K ohms for a humbucker or 250K ohms for a single coil you have a lower input impedance for the pickup to feed. 1Meg ohm times 500K (K equals 1000) ohms divided by 1Meg plus 500K gives you the equivalent input impedance of 333.3K ohms for humbucker and 200K ohms for a single coil. You want the output impedance of the pickup the be about one tenth the load impedance to not affect the sound quality too much. That means that the maximum humbucker impedance should be about 33K ohms for a humbucker and 20K ohms for a single coil. Typically, humbuckers pickups with their two coils in series are about 8K to 10K ohms DC resistance while single coils pickups are about 7K to 8 K ohms DC resistance.

In order for Lace to make the Alumitone pickups to feed a high impedance amplifier, they used the principal of the current transformer. One very low resistance turn around a magnet or magnets at the common current summary point for the two loops. However, if you look very close you will see a laminated core with two round coils about 1 inch long and about .25 inch diameter. This is a current transformer with the aluminum frame acting as a single turn primary and the two 15,000 turn coils wired in parallel acting as a 7,500 turn coil to feed a high impedance amplifier.

Joseph J. Rogowski

[nickceulemans]

electrical conductors crossing at right angles don't magnetically couple

Hi Helmholtz,

I could not establish continuity through the test coil itself yesterday. (But I believe this is mainly due to me not being able to strip the enamel from the magnet wire without destroying the wire itself and not having a continuity function on my very old multi meter... fortunately there are many Youtube videos on these topics)

I always thought the laminated core e.g. Lace uses, was there mainly to attach/assemble the coils to the aluminum frame. My reasoning was that by leaving this step out I could "extract" more of the electrical 'pulses' directly from the alu loop to the copper coil... (excuse me for my non electro vocabulary)

I will do some more research on the effect you described above. Using a laminated core to attach the coil to the frame is exactly what Lace's Patent describes, and that is what I wanted to get away from.

Just for experimentation I will try to have a working coil and see if can get any sound/signal from it at all. Basically the instrument I am building is all about finding something new,...

Nick