transducer / buzzer as a guitar pickup

[wip]

i am wondering if it would be possible to use a buzzer / transducer as a guitar pickup. right now i have crack open one and put a small magnet on it: i can read 30mV rms when playing a string. i guess it would be possible to build a preamp to bring that closer to 1V / 2V but what about the impedance? the buzzer i am using is 50 ohms, like this one https://www.digikey.ca/product-detail/en/GT-111P/433-1020-ND/479666

does that make any sense, if yes i would like to know more about the preamp / buffer / impedance / filtering.

thanks for your time!

 

[Mike odom]

I'm guessing the buzzer wouldn't make a good pickup, as it's probably very narrow frequency selective.

 

[wip]

Hi Mike,

Thanks for your reply. I am not sure where to find this information, but i can tell you that i wouldn't mind if the buzzer is able to detect something like 82Hz to 2000Hz. So maybe I just need a high-pass filter in the preamp to clean the signal as the buzzer will cut the high frequency (just brainstorming here, i am just beginning to study this).

 

[audioguru]

The magnetic buzzer will pickup only a few frequencies near 2048Hz. It will simply beep and sound awful.
Many people have used the piezo wafer from a piezo transducer or beeper glued to the guitar body. It picks up the audio vibrations and sounds good. There are articles showing how to do it in You Tube and Instructables.

 

[wip]

audioguru, 28002 messages that is incredible, thank you!

let say i am satisfied with the quality of the buzzer. what is the next step for me in general knowing that the coil resistance is 140 ohms and the signal level is 40mV rms. my guess are:

1. filter the signal to remove unwanted frequencies (not sure about this step)
2. use a preamp with gain control* to boost the signal around 400mV or more (?)
3. impedance / buffer (i am going to either plug it to an amp or in a decent soundcard)

* **broken link removed**

thanks!

 

[audioguru]

The mechanical magnetic buzzer RESONATES at 2048Hz so that will be its output when it picks up sounds or picks up the motion of steel guitar strings.
If you filter out the 2048Hz then the output will be almost nothing.
How do you know its output voltage?

EDIT: I see you posted a schematic. Why does it use so many Jfets? Usually a guitar NORMAL magnetic pickup feeds a single Jfet like this one:

 

[wip]

How do you know its output voltage?

I just observed the output of the buzzer on my scope when it's very close to a vibrating string. About the filtering i should simply leave this high frequency, but maybe it would be a good idea to filter the very low frequency (to avoid hum (50hz))? As for the preamp, i was looking for a preamp with gain control and this one look right to me, but i don't know why that many Jfets

 

[audioguru]

Hum pickup is caused by using unshielded wiring because then the wires are antennas that pickup hum and other interference. ALL audio signals use shielded audio cable.

The simple guitar pickup preamp I posted says that its gain is low because the output level of a guitar pickup is pretty high.
Some guitar pickups have a gain control and all amplifiers have a volume control.

Why are you trying to make a guitar pickup from a mechanical magnetic buzzer?

 

[wip]

Why are you trying to make a guitar pickup from a mechanical magnetic buzzer?

I am building actuated guitar and i want to experiment a bit with the pickup (that's why i don't mind about the quality).

My last question is about impedance. If the magnetic buzzer coil resistance is 40 ohms to 140 ohms, do i have to take care of the impedance / buffering (knowing that i am connecting this in a soundcard)? My "real" guitar pickup have a resistance of 9.2k - that's quite huge compared to the buzzer coil resistance.

 

[Nigel Goodwin]

I am building actuated guitar and i want to experiment a bit with the pickup (that's why i don't mind about the quality).

My last question is about impedance. If the magnetic buzzer coil resistance is 40 ohms to 140 ohms, do i have to take care of the impedance / buffering (knowing that i am connecting this in a soundcard)? My "real" guitar pickup have a resistance of 9.2k - that's quite huge compared to the buzzer coil resistance.

No, you don't impedance match, you feed a low impedance source into a high impedance load, to gives maximum voltage transfer.

It's also no use measuring DC resistance, it's very different from impedance.

 

[audioguru]

I never heard of an "actuated guitar".
Are the strings plucked by a machine? OK, I saw some videos about it on You tube.

A buzzer "does some work" so it has a low resistance to make enough power to do the work.
A real guitar pickup does not do any work so its sensitivity is increased by using a very long length of very thin wire which has a high resistance. A real guitar pickup has a very high impedance (AC resistance) so it feeds a preamp that has an input impedance of at least 1M ohms.

 

[wip]

No, you don't impedance match, you feed a low impedance source into a high impedance load, to gives maximum voltage transfer.

It's also no use measuring DC resistance, it's very different from impedance.

I need to amplify the signal produced by the buzzer (x10) so i was going to use an op-amp to do the job, but looking at the datasheet (ne5532) i see that the minimum input impedance is 30k ohms. I really don't know about all that stuff, but can i simply feed the buzzer to this op-amp with a gain of 10 and feed that to my soundcard (without buffering / voltage-follower, filtering)?

 

[audioguru]

Does the mechanical buzzer have its own magnet? Did you remove the armature from the buzzer? Does your guitar have steel strings? Will you use a separate buzzer for each string? Will each string fit close to the magnet and the coil?

Hook up a buzzer directly to the input of your sound card and try it and since most sound cards have an input designed for an electret microphone then there will be plenty of gain. You will hear if you need more gain from a preamp and hear if filtering is needed.

 

[Nigel Goodwin]

I need to amplify the signal produced by the buzzer (x10) so i was going to use an op-amp to do the job, but looking at the datasheet (ne5532) i see that the minimum input impedance is 30k ohms. I really don't know about all that stuff, but can i simply feed the buzzer to this op-amp with a gain of 10 and feed that to my soundcard (without buffering / voltage-follower, filtering)?

The minimum input impedance certainly isn't 30K - I suspect you don't understand what you're reading.

But 30K would be fine anyway.

If you use the opamp in inverting mode the input impedance is the input resistor, so 10K for that would give 10K input impedance, and 100K feedback resistor would give a gain of ten.

 

[wip]

Does the mechanical buzzer have its own magnet? Did you remove the armature from the buzzer? Does your guitar have steel strings? Will you use a separate buzzer for each string? Will each string fit close to the magnet and the coil?

Hook up a buzzer directly to the input of your sound card and try it and since most sound cards have an input designed for an electret microphone then there will be plenty of gain. You will hear if you need more gain from a preamp and hear if filtering is needed.

Yes here's the buzzer:

My goal is to use a buzzer for each string and i am trying to design a PCB that will hold the 6 buzzer as close as possible from the string (using more coil resistance = more sensible but the higher i can get is around 140 ohms). My soundcard is a recording interface (10 inputs - XLR - line input) and when connecting directly the buzzer: i can almost hear it when cranking up input / output. 40mV rms is not enough for line level i guess.

Here's a preamp that i found on the web:
Single-transistor pre-amp for very-low-impedance Guitar Pickups
https://www.joebrown.org.uk/wp/?p=7225

But I ran the simulation in ltspice and the signal is more towards the negative side no matter how big the caps is at the ouput:

 

[wip]

If you use the opamp in inverting mode the input impedance is the input resistor, so 10K for that would give 10K input impedance, and 100K feedback resistor would give a gain of ten.

So I will try it, using a NE5532 in inverting mode. But is the input resistor should match the buzzer coil resistance (40 ohms)?

 

[Nigel Goodwin]

So I will try it, using a NE5532 in inverting mode. But is the input resistor should match the buzzer coil resistance (40 ohms)?

NO! - as I said above it's important to feed a low impedance in to a high one - and you don't even know the impedance, it's NOT the same as DC resistance.

I would use the 10K and 100K I mentioned above, although it's not at all critical.

 

[audioguru]

A buzzer with a DC resistance of 40 ohms might have an AC impedance of 4000 ohms or more. You NEVER match impedances because you want to keep the small signal voltage produced and not throw it away. For a 4k ohms pickup then the preamp should have an input impedance of at least 40k ohms.

The transistor preamp you found has an extremely high voltage gain (and very high distortion) because the impedance of your signal generator is ZERO ohms. If the source impedance is 4k ohms (parallel to the 1k input of the preamp) then the voltage gain will be much less and the very low input impedance of the preamp will kill the output level of the pickup. Use a non-inverting opamp (it has a high input impedance) instead.

 

[audioguru]

Is the metal core in the coil from your buzzer a magnet?

 

[wip]

Yes the little disk is a weak magnet. Do you think I should try to use a rare earth magnet to increase sensibility? Well, i just made a test and the string is too much attracted.

I think I will begin the op-amp circuit and make some test (will post back result). I also need to go to the library to find a book on impedance and electronics in general