Low Impedance Pickup Research

[surdopickups]

Antonio,

Getting a more acoustic sound is a balancing act with this current transformer (CT) type of pickup.

1. The string loop wire gauge will determine how much current is being induced in the string loop around the magnet. Thicker wire will produce more output level and will have a lower output impedance from the current transformer.

2. Thicker solid wire will have a lower frequency skin effect. This is where your ear can hear a sound difference between wire sizes as well as wire type with stranded wire having less of the skin effect.

3. The string loop joint connection needs to be a good low resistance connection to generate the most current for the best current transformer output level.

4. Having good tools to measure the output impedance of the current transformer is necessary for getting a good mental model of changes made in wire size, type and joint connection to the output impedance and high low frequency sound balance. I use the Extech 380193 LCR meter. You can use other ways to measure the output impedance but you need to keep this in you mind as you change the variables to achieve that acoustic sound that you are seeking.

5. Here is an example. If I use AWG 8 solid wire string loop 8 inches long that is 400 micro ohms with a 500 turn CT, the output impedance should be near 100 ohms depending on the quality of the string loop joint and the frequency of my measurement. If I use a 750 turn CT the output impedance will go up to about 225 ohms. This is near the highest output impedance to drive a typical 2400 ohm XLR mic input impedance.

6. The mechanics of making a good low resistance string loop using very thick wire requires a creative way to make a good low resistance string joint without damaging the CT with soldering heat or mechanical fracture of the CT housing by bending thick solid wire through the CT hole. Get copper tubing to fit the CT hole. Use a tube cutter to get parallel tube cuts. Use good crimp on wire connectors to put a nut and screw through the copper tube to complete the string loop. By measuring the output impedance you can see the lowest resistance connection will have the lowest output impedance. This set up allows you to quickly change CTs with 500, 750 and 1000 turns and listen to the sound differences.

I hope this helps.

Joseph J. Rogowski

Joseph J. Rogowski

your advice is always valuable, and denotes your great expertise in the field, thank you very much, if I have any news in the construction of my pickups I will post them on the forum, kind regards,

Antonio Surdo

[surdopickups]

ln principle there's no reason why a single loop (+step-up transformer) PU should produce a better "acoustic sound" than a multiple turns PU (without transformer).

Drawback of single loop PUs is that the bass response suffers when the loop resistance is too large.
That's a consequence of having to use a transformer.

the single loop pickup is very fascinating because of the construction possibilities it offers, however I think I will continue to focus on the classic pickups, single coil or humbucker, thank

[Helmholtz]

ln principle there's no reason why a single loop (+step-up transformer) PU should produce a better "acoustic sound" than a multiple turns PU (without transformer).

Drawback of single loop PUs is that the bass response suffers when the loop resistance is too large.
That's a consequence of having to use a transformer.

[bbsailor]

certainly! it is as you say.
the ideal would be to connect to pin 1 XRL the ring and at the same time the ring build it in the shape of 8 . However, after the countless tests I have done, with magnets different both in shape and type (neodymium ferrite, round or square, different even in size) the results although very good, I am not completely satisfied, there is still something missing in the sound I can achieve, to get closer and closer to the naturalness of acoustic sound.

Antonio,

Getting a more acoustic sound is a balancing act with this current transformer (CT) type of pickup.

1. The string loop wire gauge will determine how much current is being induced in the string loop around the magnet. Thicker wire will produce more output level and will have a lower output impedance from the current transformer.

2. Thicker solid wire will have a lower frequency skin effect. This is where your ear can hear a sound difference between wire sizes as well as wire type with stranded wire having less of the skin effect.

3. The string loop joint connection needs to be a good low resistance connection to generate the most current for the best current transformer output level.

4. Having good tools to measure the output impedance of the current transformer is necessary for getting a good mental model of changes made in wire size, type and joint connection to the output impedance and high low frequency sound balance. I use the Extech 380193 LCR meter. You can use other ways to measure the output impedance but you need to keep this in you mind as you change the variables to achieve that acoustic sound that you are seeking.

5. Here is an example. If I use AWG 8 solid wire string loop 8 inches long that is 400 micro ohms with a 500 turn CT, the output impedance should be near 100 ohms depending on the quality of the string loop joint and the frequency of my measurement. If I use a 750 turn CT the output impedance will go up to about 225 ohms. This is near the highest output impedance to drive a typical 2400 ohm XLR mic input impedance.

6. The mechanics of making a good low resistance string loop using very thick wire requires a creative way to make a good low resistance string joint without damaging the CT with soldering heat or mechanical fracture of the CT housing by bending thick solid wire through the CT hole. Get copper tubing to fit the CT hole. Use a tube cutter to get parallel tube cuts. Use good crimp on wire connectors to put a nut and screw through the copper tube to complete the string loop. By measuring the output impedance you can see the lowest resistance connection will have the lowest output impedance. This set up allows you to quickly change CTs with 500, 750 and 1000 turns and listen to the sound differences.

I hope this helps.

Joseph J. Rogowski

[surdopickups]

Electrostatic shielding doesn't help with magnetically induced hum.
Complete magnetic shielding (e.g. wrapping in Mumetal foil) would stop the PU from working.
That's why hum cancelling methods (humbucker, dummy coils) were developed.

certainly! it is as you say.
the ideal would be to connect to pin 1 XRL the ring and at the same time the ring build it in the shape of 8 . However, after the countless tests I have done, with magnets different both in shape and type (neodymium ferrite, round or square, different even in size) the results although very good, I am not completely satisfied, there is still something missing in the sound I can achieve, to get closer and closer to the naturalness of acoustic sound.

[Helmholtz]

Electrostatic shielding doesn't help with magnetically induced hum.
Complete magnetic shielding (e.g. wrapping in Mumetal foil) would stop the PU from working.
That's why hum cancelling methods (humbucker, dummy coils) were developed.

[surdopickups]

surdopickups,

What is the current transformer part number and turns count?


Did you try using 2 conductor shielded cable to connect the CT to a mic input with the cable shield connected to the loop around the magnet?

Using thicker wire will provide more output. Try to keep the CT output impedance about one tenth the mic input loading resistance or impedance. A typical XLR mic will have a 2400 ohm loading effect so try to keep the CT output Impedance near 240 ohms.

Joseph J. Rogowski

I used the AS 104 TALEMA transformer, I am aware that by using some tricks like shielded cable, connecting the ring to pole 1 of the XRL socket, things will improve, but my thought is the following if we already start from a reduced noise construction because of humbucker effect, then the subsequent tricks shielded cable and connection to pole 1 of the ring, will only further improve the pickup.

best regards

Antonio Surdo

[bbsailor]

hello everyone I would like to share with you an experience of mine, I premise that I have no idea if what I am about to say has already been said by someone, I have noticed that in the case of the pickup a single coil, if this coil is folded to form a figure eight , it noteletely reduces the noise floor, it is as if there f ound a humbucker effect. I assure you that the noise reduction is remarkable, this may come in handy in improving the 1-turn pickup.

surdopickups,

What is the current transformer part number and turns count?


Did you try using 2 conductor shielded cable to connect the CT to a mic input with the cable shield connected to the loop around the magnet?

Using thicker wire will provide more output. Try to keep the CT output impedance about one tenth the mic input loading resistance or impedance. A typical XLR mic will have a 2400 ohm loading effect so try to keep the CT output Impedance near 240 ohms.

Joseph J. Rogowski

[Helmholtz]

I really like the idea. Nice example of applied physics.

[surdopickups]

If you prefer, call it a dummy coil. Still it's a hum-bucking effect.

well, I agree with your point of view, I hope it can come in handy for those who try their hand at building the 1 loop pickup , I think you can develop some nice designs for acoustic guitar.

[Helmholtz]

If you prefer, call it a dummy coil. Still it's a hum-bucking effect.

[surdopickups]

Yes, that produces a humbucker effect as the 2 parts of coil when twisted to an 8 have opposite winding directions

it is true! although in theory the second coil, let's say the virtual one near the transformer , is before magnets, therefore we should not talk about real humbucker

[Helmholtz]

I have noticed that in the case of the pickup a single coil, if this coil is folded to form a figure eight , it noteletely reduces the noise floor, it is as if there f ound a humbucker effect.

Yes, that produces a humbucker effect as the 2 parts of coil when twisted to an 8 have opposite winding directions

[surdopickups]

hello everyone I would like to share with you an experience of mine, I premise that I have no idea if what I am about to say has already been said by someone, I have noticed that in the case of the pickup a single coil, if this coil is folded to form a figure eight , it noteletely reduces the noise floor, it is as if there f ound a humbucker effect. I assure you that the noise reduction is remarkable, this may come in handy in improving the 1-turn pickup.

[bbsailor]

Funny story, I remember that thread, and I actually originally bought the 2" aluminum bar stock from the hardware store with the intent of using it as fretboard material for the "low resistance return path". But since then my guitar building ambitions have changed a bit so I'm now planning to make a more conventional wood neck.

Alex,

Try to use the thick metal truss rod as the ground return connected to a brass or copper nut to bring the common ground end of the strings back into the body area. The rule of thumb should be to make the total resistance of the ground return to be about one tenth of the string resistance to minimize resistive connection losses to the string transformer.

To start tinkering with this new pickup concept just use alligator clip wire to connect a single guitar string behind the nut and the bridge to the 8 ohm side of the transformer. Just make sure that no other strings are shorting out your test string as it will vastly reduce the output level.

Have fun!

Joseph J. Rogowski