Low Impedance Pickup Research

[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.

[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]

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]

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

[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]

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

[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

[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

[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]

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.

[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

[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.

[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

[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

[bbsailor]

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

Here are some design tips to consider with toroid CT.

1. Find a round solid wire that snugly fits the toroid opening. If it is slightly loose put some tape on the wire to snug the fit up.
2. Use AWG 8 solid .125 inch wire to make the string loop about 8 to 8.5 inches long. Make a hairpin turn in this solid wire to match the width of your magnets. If the magnets a made of conductive metal insulate one side to prevent shorting the string loop. The CT should be spaced about .75 to 1 inch from the edge of the magnet. This allows you to bend down the solid wire string loop to go under the guitar top on an acoustic guitar to place the pickup near the end of the fingerboard.
3. Drill the larger solid wire in step 1 above to fit the AWG 8 solid wire snugly in the holes at a perfect right angle just wide enough to match the CT thickness. In the two round ends of the thick toroid core wire drill a small hole to thread and add a hex head set screw to maintain a tight fit and a low resistance joint now and over time.
4. When the pickup is tested for a low resistance joint by measuring the output impedance, paint the joint or cover it with a thick rubber like covering insulate the joint from moisture and decay over time.
5. On an acoustic guitarI have used this setup to not drill any holes in the guitar.
5.1 Use two ice cream like sticks to mount the pickup to the hole opening with small self stick pads on the top stick to prevent scratching the guitar finish.
5.2 Solder about a 1 foot length of 2 conductor shielded cable attached to a female tip ring sleeve connector. The shield is connected to the sleeve connection with the tip and ring attached to the CT output. Attach the female connector to a small piece of plastic like a cut up credit card with a single small hole. Remove the guitar strap attachment pin on the heel of the neck and install the female connector on the plastic card mount.
5.3 Make an male attachment cable to match the mounted female connector to go to an XLR mic connector.


This should work and allow a fast addition to a guitar with no change to the guitar.

Different guitar strings, turn ratio CTs and magnet strength and types will all affect the final tone that you hear.

Joseph J. Rogowski