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Thread: Low Impednace type pickups. What am I missing?

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    Low Impednace type pickups. What am I missing?

    Hi, before I start with my question, let me preface it by saying I'm something of a luddite when it comes to electronics. I have a soldering iron, and a lot of enthusiasm to want to make things, but sadly I'm like a blind man driving a car in this area.
    I usually work with inanimate lumps of wood, but recently have been fascinated by the idea of Alumitone pickups, and was fascinated to see people on Youtube making their own with relative ease - so naturally I thought "How hard can it be?" and decided to give it a go...

    The Youtube videos all seem to suggest that all you need is a magnet around which you loop a bit of copper a few times, then hook that up to a transformer input, then run the output to the jack of your amp...
    They all make it seem so simple...

    So I bought these bar magnets...
    https://www.amazon.co.uk/gp/product/B00TACG4ZE
    And this wire...
    https://www.amazon.co.uk/gp/product/B07DYF53ZN
    And I went to work first insulating the outside of the magnet with tape, then I wrapped it with a dozen loops of the wire...
    The Youtube videos only wrap once with a heavier guage wire, but I figured more wraps mus be better surely, right? (like I say, I'm flying blind here so don't shoot me if I'm wrong lol)...

    I made myself a small transformer, again following youtube tutorials and hooked it all up, but there was no sound...
    I tried the wiring in as many different configurations as I could but no sound...

    So I figured, maybe my transformer isn't powerful enough, or maybe I did something wrong when making it...
    Maybe I need to get a more powerfull transformer to ramp up the signal more and give it more punch...
    So I bought one of these transformers...
    https://www.amazon.co.uk/gp/product/B0719KWX82
    My thinking was that it should give the signal to the amp enough oomph to at least cerate an audible sound...

    Sadly, again, nothing...

    Am I missing something really obvious?
    Is there a vital component that I'm forgetting about?
    Are the parts I'm using not suitable for this type of application?
    Should I just throw my soldering iron in the bin and stick to banging bits of wood together instead?

    I'd really appreciate any help or suggestions.

    Many thanks,
    Fat Sam.

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    Quote Originally Posted by FatSam View Post
    Hi, before I start with my question, let me preface it by saying I'm something of a luddite when it comes to electronics. I have a soldering iron, and a lot of enthusiasm to want to make things, but sadly I'm like a blind man driving a car in this area.
    I usually work with inanimate lumps of wood, but recently have been fascinated by the idea of Alumitone pickups, and was fascinated to see people on Youtube making their own with relative ease - so naturally I thought "How hard can it be?" and decided to give it a go...

    The Youtube videos all seem to suggest that all you need is a magnet around which you loop a bit of copper a few times, then hook that up to a transformer input, then run the output to the jack of your amp...
    They all make it seem so simple...

    So I bought these bar magnets...
    https://www.amazon.co.uk/gp/product/B00TACG4ZE
    And this wire...
    https://www.amazon.co.uk/gp/product/B07DYF53ZN
    And I went to work first insulating the outside of the magnet with tape, then I wrapped it with a dozen loops of the wire...
    The Youtube videos only wrap once with a heavier guage wire, but I figured more wraps mus be better surely, right? (like I say, I'm flying blind here so don't shoot me if I'm wrong lol)...

    I made myself a small transformer, again following youtube tutorials and hooked it all up, but there was no sound...
    I tried the wiring in as many different configurations as I could but no sound...

    So I figured, maybe my transformer isn't powerful enough, or maybe I did something wrong when making it...
    Maybe I need to get a more powerfull transformer to ramp up the signal more and give it more punch...
    So I bought one of these transformers...
    https://www.amazon.co.uk/gp/product/B0719KWX82
    My thinking was that it should give the signal to the amp enough oomph to at least cerate an audible sound...

    Sadly, again, nothing...

    Am I missing something really obvious?
    Is there a vital component that I'm forgetting about?
    Are the parts I'm using not suitable for this type of application?
    Should I just throw my soldering iron in the bin and stick to banging bits of wood together instead?

    I'd really appreciate any help or suggestions.

    Many thanks,
    Fat Sam.
    Sam,

    The Alumitone pickup uses the aluminum metal frame of the pickup as the low resistance ¬“string loop¬” feeding two coils mounted under the frame that each have about 15000 turns of very fine wire. They are connected in parallel and are listed as having about 2500 ohms, meaning that each coil is about 5000 ohms. These pickups are designed to be used on high impedance guitar amps.

    True low impedance pickups target the traditional low impedance microphone inputs listed as 150 ohms but can range from about 100 ohms to about 300 ohms. The typical microphone XLR input impedance is about 2400 ohms to act as a light load on low impedance inputs up to about 240 ohms, having an actual load 10 times higher than the actual output impedance.

    Low impedance pickups using a transformer are using a current based concept rather than a voltage based concept. For the current based approach to work, you need a string loop with very low resistance to develop more current in the primary transformer string loop with the magnet in the center. This means using very heavy copper wire with a very very, very low resistance joint to maintain a high current in the string loop.

    AWG 8 wire has 52 micro ohms per inch resistance. A typical. String loop, including the part that goes through the transformer is about 8 inches long. 52 micro ohms is .000052 times 8 or 416 micro ohms. If you use a 500 turn current transformer with one turn on the transformer primary, you must square the turns ratio to calculate the approximate output impedance. 416 micro ohms times 250,000 is 104 ohms which targets a microphone input very well. This assumes that the AWG 8 wire string loop has a very, very, very low resistance joint forming the string loop.

    Most of the YouTube videos do not mention these details. See my thread ¬“Low impedance pickup research¬” for more details.

    Use a Triad CSE-186L current transformer but remove the primary windings of three turns of AWG 16 wire to reveal an opening that will allow the AWG 8 wire to be bent into a hairpin loop to extend under the guitar strings with a magnet in the center. The challenge is to make a good low resistance joint to complete the string loop using a copper crimp sleeves with silver solder. Use two conductor shielded microphone cable with the two transformer outputs going to the inner conductors and the shield going to the string loop. On the XLR side make pin 1 the shield connection, pins 2 and 3 the transformer connections. This design allows you to slip the pickup under the strings to try it out with any changes to your guitar. Just feed it to an XLR microphone input or an XLR Shure A95U series mic matching transformer.

    This should get you going in the right direction.

    Joseph J. Rogowski

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    Thanks Joseph.
    So if I understand correctly, the biggest mistake I've made is that there's too much resistance in the setup I've come up with?
    You've given me some good pointers to be getting on with, thanks. I'll let you know how I get on with my next experiments tonight...

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    ... or maybe I did something wrong when making it...
    You use not the appropriate thickness of the wire for pickup.
    Thick wire 28 AWG (0.3mm) = lower resistance of the coil = low output
    Thin wire 42 AWG (0.06mm) or 44 AWG (0.05mm) = higher resistance of the coil = high output


    https://www.google.com/search?q=fender+pickup+wire+gauges

    http://www.ohmslawcalculator.com/awg-wire-chart

    https://en.wikipedia.org/wiki/American_wire_gauge

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    Thick wire 28 AWG (0.3mm) = lower resistance of the coil = low output
    Thin wire 42 AWG (0.06mm) or 44 AWG (0.05mm) = higher resistance of the coil = high output
    Sorry, these equations are simply wrong. Output cannot be read from coil resistance. Especially single primary loop transformer PUs like the Alumitone need a heavy gauge/very low resistance primary loop for good efficiency and bass response and still output is mainly determined by the transformer's step-up ratio.

    In standard "high impedance" PUs output is mainly determined by the number of turns and the strength of the magnetic field. Wire gauge and coil resistance have very little influence on output. But even with high impedance PUs lower resistance (everything else being unchanged) will result in a slightly increased output.

    Resistance in inductive components is generally considered an undesirable property as it always causes losses.

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    Last edited by Helmholtz; 06-18-2019 at 02:26 PM.
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    Quote Originally Posted by Helmholtz View Post
    Sorry, these equations are simply wrong. Output cannot be read from coil resistance. Especially single primary loop transformer PUs like the Alumitone need a heavy gauge/very low resistance primary loop for good efficiency and bass response and still output is mainly determined by the transformer's step-up ratio.

    In standard "high impedance" PUs output is mainly determined by the number of turns and the strength of the magnetic field. Wire gauge and coil resistance have very little influence on output.
    So the primary loop - the one that wraps round the magnet needs to be heavy guage then?
    By wrapping several loops of thinner guage wire, I've actually been doing exactly the opposite of what I needed to do?

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    Quote Originally Posted by FatSam View Post
    So the primary loop - the one that wraps round the magnet needs to be heavy guage then?
    By wrapping several loops of thinner guage wire, I've actually been doing exactly the opposite of what I needed to do?
    Other than with standard PUs there is no benefit from using more than one turn for the shorted primary (sensing loop) of the "transformer PU". Rather it is important to keep the resistance of the loop extremely low.

    It is strange that you got no sound at all. Maybe wrong wiring. Can you post pictures?

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    If pickup make properly, try to the connection with the amplifier via a microphone transformer.
    At the transformer, is very important ratio between the primary and the secondary windings.
    Transformer coil with high resistance connect to amplifier.
    https://www.google.co.uk/search?q=microphone+transformer

    Some Gibson guitars series Les Paul Recording and Les Paul Signature used a transformer for the high signal level.
    http://www.flyguitars.com/graphics/lespaul.jpg

    https://www.youtube.com/watch?v=jgCEzGvBElg
    Alumitone style pickup for CBG prototype.

    If all is right as the picture the guitar must play.


    http://guitarnuts2.proboards.com/thread/7821/lace-alumitone-analysis-review

    https://www.youtube.com/results?search_query=diy+alumitone+pickup

    https://www.google.co.uk/search?q=diy+alumitone+pickup

    https://groupdiy.com/index.php?topic=27929.0

    http://www.freepatentsonline.com/6897369.pdf

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    Last edited by vintagekiki; 06-18-2019 at 02:12 AM.

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    Quote Originally Posted by Helmholtz View Post
    It is strange that you got no sound at all. Maybe wrong wiring. Can you post pictures?
    Will do, I just realised my phone battery is dead so I need to find a charger first LOL.
    For what it's worth, I had a rummage around for a heavier piece of wire or metal to make the loop from to see if that makes a difference.
    I have a piece of aluminium that I'm going to cut into a shape fitted to my bar magnet later and try that.
    In the meantime, I found a piece of steel bar (thin enough to bend in a vice) in the workshop and bent it around my magnet, but still nothing. I'd have thought that would be pretty conductive, but perhaps there's a reason why aluminium and copper tend to be the metals of choice.
    I'll get to work cutting the aluminium tomorrow to see if that works.

    With regard to the wiring. To the best of my ability to tell, I've wired it exactly as in the videos I watched on Youtube.
    The guy inthe video used a transformer from a wall charger, but I figured a transfromer's a transformer right, so this Amazon bought one should work just fine so long as it's a step-up transformer - I could be wrong on that as I'm making assumptions here based on uneducated logic LOL.
    I even assumed errors on my part and experimented with wiring the transformer up backwards just in case I'd mixed up the inputs and outputs.

    I wonder if I've got a faulty transformer unit?

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    So I bought one of these transformers...
    https://www.amazon.co.uk/gp/product/B0719KWX82
    My thinking was that it should give the signal to the amp enough oomph to at least cerate an audible sound...
    B0719KWX82 is not a transformer this is a module voltage generator and do not work for what you want.

    ... experimented with wiring the transformer up backwards just in case I'd mixed up the inputs and outputs ...
    In the case of a transformer the transformer input has low resistance and a pickup is connected to it, and the transformer output has high resistance and amplifier is connected to it

    Tip
    If you are in dilemma or doubt in the transformer, connect the pickup direct to the mixer microphone input because this input is predicted for "small" signals (a few milivolts)

    If mixer has a signal, the pickup is correct, the problem is in the interface between pickup and amplifiers (inadequate transformer)

    ... I wonder if I've got a faulty transformer unit? ...
    Question
    Do you use charger, power adapter or transformer unit?

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    I have a piece of aluminium that I'm going to cut into a shape fitted to my bar magnet later and try that.
    In the meantime, I found a piece of steel bar (thin enough to bend in a vice) in the workshop and bent it around my magnet, but still nothing. I'd have thought that would be pretty conductive, but perhaps there's a reason why aluminium and copper tend to be the metals of choice.
    Copper and aluminum are much better conductors than steel. When considering aluminum, don't forget that you need a closed/shorted loop with a very low resistance contact between the ends. This is best achieved using copper wire and soldering the ends. Also the loop needs to be fed through the core window of the transformer before joining the wire ends. The loop needs to become the primary winding of the transformer, that's why I like to call these "transformer PUs".
    With this kind of PUs it would make no sense to just connect the loop ends to the input of a transformer.

    The guy inthe video used a transformer from a wall charger, but I figured a transfromer's a transformer right, so this Amazon bought one should work just fine so long as it's a step-up transformer .
    The part in the Amazon link is no transformer as vintagekiki already noted. It is a step-up converter (a switched mode power supply) generating very high voltages (200.000V).

    Regarding suitable transformers I would go with bbsailor's recommendations.

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    Last edited by Helmholtz; 06-18-2019 at 06:51 PM.
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    Thanks for all the advice guys... The upshot of all this is that after lots and lots of experiments, I just couldn't get it to work - not satisfactorilly anyway - so I've just accepted the fact that I'm a woodworker, not an electrician, and bought a set of Hot Rails instead LOL...
    I figure Seymour Duncan are probably a lot better at this stuff than I am

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