low-impedance pickups thin

[surdopickups]

I built the pickups ultra thin further reduce the impedance.
material used:
neodymium magnets
* wire awg 41 polys
* turns 400
278 ohm resistance obtained
balanced cable (2 + ground)
xrl male connector for direct connection to mixer
end result sounds really high quality
I'm happy with the result

[charrich56]

I am glad you built a successful low impedance pickup. I personally love the high fidelity sound they can reproduce.

Do you have a way to measure the inductance and winding capacitance of the pickup?

The only reason I am asking is that with a low impedance pickup it is possible to have a ultrasonic resonant peak which might cause issues with some, not all, microphone input preamps. With those numbers it would be easy to model the pickup and see if the resonance would be an issue, and find the optimum termination resistance for the pickup.

If your mic-level input impedance is 10K or less though, it shouldn't be much of a problem however.

If you have room on the coil and want to experiment further, you might try going lower on the wire gauge (#32 to #36 AWG) and be able to get some more windings without the DC resistance going up, for a bit more output.


Take care and enjoy the sound,

Charlie

[surdopickups]

I am glad you built a successful low impedance pickup. I personally love the high fidelity sound they can reproduce.

Do you have a way to measure the inductance and winding capacitance of the pickup?

The only reason I am asking is that with a low impedance pickup it is possible to have a ultrasonic resonant peak which might cause issues with some, not all, microphone input preamps. With those numbers it would be easy to model the pickup and see if the resonance would be an issue, and find the optimum termination resistance for the pickup.

If your mic-level input impedance is 10K or less though, it shouldn't be much of a problem however.

If you have room on the coil and want to experiment further, you might try going lower on the wire gauge (#32 to #36 AWG) and be able to get some more windings without the DC resistance going up, for a bit more output.


Take care and enjoy the sound,

Charlie

Thanks Charlie,
very interesting topic,
really very beautiful, low impedance pickups.
I am able to perform the measurements of resistance, inductance and capacitance,
I will provide the readings of electrical measurements obtained as soon as possible,
Also to have your response.
Thanks again for the advice.

Antonio Surdo

[surdopickups]

hello Charlie,
if I have not made mistakes
these values are
278 ohm resistor
20 mH inductance
- 0,15 microFarad capacity

what do you think is correct the negative value of capacity given by the multimeter RLC
thanks

[surdopickups]

I am glad you built a successful low impedance pickup. I personally love the high fidelity sound they can reproduce.

Do you have a way to measure the inductance and winding capacitance of the pickup?

The only reason I am asking is that with a low impedance pickup it is possible to have a ultrasonic resonant peak which might cause issues with some, not all, microphone input preamps. With those numbers it would be easy to model the pickup and see if the resonance would be an issue, and find the optimum termination resistance for the pickup.

If your mic-level input impedance is 10K or less though, it shouldn't be much of a problem however.

If you have room on the coil and want to experiment further, you might try going lower on the wire gauge (#32 to #36 AWG) and be able to get some more windings without the DC resistance going up, for a bit more output.


Take care and enjoy the sound,

Charlie

I am not very clear how the resonance peak can give problems to the preamplifier
can you give me some information or useful links to know more about

[charrich56]

Antonio,

I think your capacitance may be measuring very high. A more typical figure for measuring the capacitance to ground of just the windings would be approximately 100-250 picofarads (pF).


Using a simple model for the pickup in CircuitLab (an electronics simulator) and plugging in your values, we can run a frequency response curve for the pickup for a 50 K ohm load (input impedance of the mic preamp) and for 10 K ohm load as follows:

Here's the circuit:


Here's the response for a 10 K load:


Here's the response for a 50 K load:


As you can see, there is a 14 dB ultrasonic spike in the response with a 50K load. The strings will have near zero energy at this frequency but electromagnetic noise in the environment could be picked up and sent to your preamp. A single light dimmer within 20 feet could create enough energy at exactly the right frequencies to be a problem. With input impedances higher than 50K this spike could be even larger and EMI/RFI noise could overload the input stage of the mic preamp. The mic preamp may or may not be able to filter it out but you don't want to find out the hard way. This issue is negligible with a 10 K Ohm load but this illustrates that shielding(less important) and a humbucking design (more important) are also still good ideas for low impedance pickups, along with making sure of the correct termination impedance.

Fortunately most mic inputs are 10 to 20K input impedance so this should not be a big issue for you. However if you go to an onboard preamp (which I have been working with) the input impedance of the preamp is a large factor and a termination resistor would be used to "damp" the peak or even assist in creating an audio resonant peak of the right height so that by also adding capacitance, you could simulate in a flexible way the response of conventional high impedance pickups.

This is the same type of LCR resonant peak which in high impedance pickups, is in the audio range, and cannot easily be compensated for to get a high fidelity output, since all the high frequencies above the resonant peak, fall off very rapidly, and you can't move the resonant peak outside the range of human hearing.

You can move the resonant peak down with additional capacitance, but you cannot move it up beyond the self-resonance caused by the pickup's inductance interacting with the winding capacitance. That is why if you start with a low or medium-Z pickup which has self-resonance that is above the audio range, you can bring it down anywhere you want to in the audio range, or just make sure it is "out of the way" for a high-fidelity output.

Lemme has a good introduction to the subject of pickups and self-resonance:
http://buildyourguitar.com/resources/lemme/

I didn't want to bring up a concern which may not really exist for you, but wanted you to understand that this could be an issue with low impedance pickups. Personallly I am completely sold on the high fidelity aspect of low-Z pickups and have been working with shaping the responses to allow emulation of conventional high-Z pickups. IMHO Low-Z is the best way to go if you want to do both of these things with one pickup.

-Charlie

[surdopickups]

Antonio,

I think your capacitance may be measuring very high. A more typical figure for measuring the capacitance to ground of just the windings would be approximately 100-250 picofarads (pF).


Using a simple model for the pickup in CircuitLab (an electronics simulator) and plugging in your values, we can run a frequency response curve for the pickup for a 50 K ohm load (input impedance of the mic preamp) and for 10 K ohm load as follows:

Here's the circuit:
[ATTACH=CONFIG]31556[/ATTACH]

Here's the response for a 10 K load:
[ATTACH=CONFIG]31557[/ATTACH]

Here's the response for a 50 K load:
[ATTACH=CONFIG]31558[/ATTACH]

As you can see, there is a 14 dB ultrasonic spike in the response with a 50K load. The strings will have near zero energy at this frequency but electromagnetic noise in the environment could be picked up and sent to your preamp. A single light dimmer within 20 feet could create enough energy at exactly the right frequencies to be a problem. With input impedances higher than 50K this spike could be even larger and EMI/RFI noise could overload the input stage of the mic preamp. The mic preamp may or may not be able to filter it out but you don't want to find out the hard way. This issue is negligible with a 10 K Ohm load but this illustrates that shielding(less important) and a humbucking design (more important) are also still good ideas for low impedance pickups, along with making sure of the correct termination impedance.

Fortunately most mic inputs are 10 to 20K input impedance so this should not be a big issue for you. However if you go to an onboard preamp (which I have been working with) the input impedance of the preamp is a large factor and a termination resistor would be used to "damp" the peak or even assist in creating an audio resonant peak of the right height so that by also adding capacitance, you could simulate in a flexible way the response of conventional high impedance pickups.

This is the same type of LCR resonant peak which in high impedance pickups, is in the audio range, and cannot easily be compensated for to get a high fidelity output, since all the high frequencies above the resonant peak, fall off very rapidly, and you can't move the resonant peak outside the range of human hearing.

You can move the resonant peak down with additional capacitance, but you cannot move it up beyond the self-resonance caused by the pickup's inductance interacting with the winding capacitance. That is why if you start with a low or medium-Z pickup which has self-resonance that is above the audio range, you can bring it down anywhere you want to in the audio range, or just make sure it is "out of the way" for a high-fidelity output.

Lemme has a good introduction to the subject of pickups and self-resonance:
BuildYourGuitar.com :: The Secrets of Electric Guitar Pickups

I didn't want to bring up a concern which may not really exist for you, but wanted you to understand that this could be an issue with low impedance pickups. Personallly I am completely sold on the high fidelity aspect of low-Z pickups and have been working with shaping the responses to allow emulation of conventional high-Z pickups. IMHO Low-Z is the best way to go if you want to do both of these things with one pickup.

-Charlie

really very interesting, thanks for the clarification, were clear and comprehensive.
Well done.
I plan to build a pickup overall thickness <5 mm.
Neodymium magnets
* 2 coils stacked (stacks pickups)
steel plates
connection cable and balanced XLR connector xrl
should be an interesting job, with decent results.
insert photos as soon as possible

[bea]

Just another question: what magnets do You use? Diameter, thickness, strength?

[surdopickups]

Just another question: what magnets do You use? Diameter, thickness, strength?

sometimes use magnets
legth = 20 mm
width= 10 mm
height= 2 mm

N35 N 45 for pickups with magnets differentiated

[bea]

THX

Beate

[MisterBzr]

I built the pickups ultra thin further reduce the impedance.
material used:
neodymium magnets
* wire awg 41 polys
* turns 400
278 ohm resistance obtained
balanced cable (2 + ground)
xrl male connector for direct connection to mixer
end result sounds really high quality
I'm happy with the result

Surdopickups,

I've stumbled on this thread. Cool.
Do you happen to have some pictures of the pickups?
Do you make them single coil or humbucking?
Thanks in advance.

Hans

[surdopickups]

Surdopickups,

I've stumbled on this thread. Cool.
Do you happen to have some pictures of the pickups?
Do you make them single coil or humbucking?
Thanks in advance.

Hans

you can view different massively images and some videos from the pages of my blog or facebook knows
http://surdopickups.blogspot.it/p/gypsy-pickups.html
https://www.facebook.com/Surdopickups

[MisterBzr]

Thank you!

[MisterBzr]

I've build a prototype of a thin pickup using:
4x 25x5x3mm Neod. magnets
2x piece of 1.6mm cardboard
appr. AWG 44 / 0.05mm copper wire from a salvaged inductor

I've put two staples on the side of one piece of cardboard to use as soldering points. Then I glued the magnets on the first piece of cardboard. I let the magnets provide their own pressure by placing a metal piece under the cardboard. When the glue dried I glued on the second piece of cardboard.
I've wound 250 turns and got a dc resistance of 274 ohm.
I then soldered the ends of the wire and a microphone cable on the staples.

The sound is very good and because of the balanced input their is hardly any noise / hum.
I'm planning to use a slightly thicker wire (0.1mm) and experiment with the number of turns, although I want to stay under the 300 ohms.
Hans

[surdopickups]