Lower output and very poor bass response which you can fix by shunting capacitance across the piezo transducer..
Anything up to and including 22M input impedance is not too uncommon with piezo transducers, and they can be voiced with a combination of appropriate shunt capacitance and resistance. (You need to decide how much bandwidth you want and where - then depending on losses incurred you may or may not need some gain.)
Something to remember is that a piezo transducer electrically looks like a capacitor, and can be modeled as a cap in series with a source in spice if you want to simulate its electrical response.. You do need to know the capacitance of that transducer first however.
There are all sorts of issues with getting them to sound good which relates to where and how they are mounted amongst other things.
I'll try to put the schematic in text:
+ on piezo (negative on piezo goes straight to ground)
|
|-resistor (value tbd)-----|-100k resistor-|
.....................................|........................|
.......................Hot on jack.............ground on jack
hope this helps. periods are place holders.
+ on piezo (negative on piezo goes straight to ground)
|
|-resistor (value tbd)-----|-100k resistor-|
.....................................|........................|
.......................Hot on jack.............ground on jack
hope this helps. periods are place holders.
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The lower impedance load will roll off the low frequencies.
The impact of the load resistance combined with the capacitance of the Piezo element form a high pass filter. See pages 14-18 of the document I linked.
This can be taken advantage of to control the low frequency response which is normally rolled off earlier in Guitar Amps than Audiophile Amps to control bass flabbiness and fartingout in some amps.
The impact of the load resistance combined with the capacitance of the Piezo element form a high pass filter. See pages 14-18 of the document I linked.
This can be taken advantage of to control the low frequency response which is normally rolled off earlier in Guitar Amps than Audiophile Amps to control bass flabbiness and fartingout in some amps.
I find Peter's explanation fallacious.
To put it kindly, there are some things that don't play well with known mechanical science.
Less kindly, the stuff about 3 stresses is simply made-up pseudoscience.
Vibration is not a stress. Bending is not a stress. Stresses on a material are tension, compression, and shear. Bending a sample of material causes tension and compression in different areas of the sample. Anyone who's studies materials in engineering school knows this.
Common piezoelectric materials respond to tension and compression, period.
Simply vibrating a sample induces tension and compression stress due only to the inertia of the material itself.
Peter has found that if one mechanically amplifies the tension and compresson forces on the piezo element due to the vibration of the instrument, the output will be greater. Adding inertia in key places and inducing bending of the element due to vibration will definitely increase the output. This can also be accomplished with various other mechanical devices such as levers, etc.
There is a little confusion as to the voltage and impedance. Guitar amps range from 75K load resistance to about 1 Megohm. There does not seem to be a historical trend in my experience. 1 Megohm seems to be OK for deep bass with most piezo pickups, 75K is too low for many. The output voltage of a piezo pickup is comparable to the output voltage of a guitar pickup, i.e. 1 or 2 volts RMS maximum with impulses up to a few volts peak.
The attenuator circuit might be helpful in flattening out the response at the expense of output voltage and signal/noise ratio. As previously mentioned, a shunt capacitor will do the same or better if one HAS to connect a piezo element directly to a medium impedance (75K) load.
Finally, Peter could create a really convincing demonstration by comparing the output of his pickup with that of a Dean Markley or Barcus Berry etc., thus proving his product claims (never mind the science).
Cheers,
Michael
To put it kindly, there are some things that don't play well with known mechanical science.
Less kindly, the stuff about 3 stresses is simply made-up pseudoscience.
Vibration is not a stress. Bending is not a stress. Stresses on a material are tension, compression, and shear. Bending a sample of material causes tension and compression in different areas of the sample. Anyone who's studies materials in engineering school knows this.
Common piezoelectric materials respond to tension and compression, period.
Simply vibrating a sample induces tension and compression stress due only to the inertia of the material itself.
Peter has found that if one mechanically amplifies the tension and compresson forces on the piezo element due to the vibration of the instrument, the output will be greater. Adding inertia in key places and inducing bending of the element due to vibration will definitely increase the output. This can also be accomplished with various other mechanical devices such as levers, etc.
There is a little confusion as to the voltage and impedance. Guitar amps range from 75K load resistance to about 1 Megohm. There does not seem to be a historical trend in my experience. 1 Megohm seems to be OK for deep bass with most piezo pickups, 75K is too low for many. The output voltage of a piezo pickup is comparable to the output voltage of a guitar pickup, i.e. 1 or 2 volts RMS maximum with impulses up to a few volts peak.
The attenuator circuit might be helpful in flattening out the response at the expense of output voltage and signal/noise ratio. As previously mentioned, a shunt capacitor will do the same or better if one HAS to connect a piezo element directly to a medium impedance (75K) load.
Finally, Peter could create a really convincing demonstration by comparing the output of his pickup with that of a Dean Markley or Barcus Berry etc., thus proving his product claims (never mind the science).
Cheers,
Michael
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A shunt capacitor would connect the hot and ground terminals on a jack, right? If I choose to use a shunt capacitor, what values would you recommend testing?
This is really intriguing me. I am going to try a few different experiments to see what suits my setup the best. I want to try the resistors, the shunt cap, straight piezo, and a buffer. Any other suggestions?
My piezos still have not arrived. Hopefully by tomorrow or Friday they will be here and I can start testing and post about what works and what doesn't.
Again, thanks everyone for the input! Keep it up! If you have any more suggestions for testing, tell me!
Well , my guitar wasn't loud enough even with 1M loading ...
So i had made myself a J201 Preamp ( not don's version )
And it got much louder , oh and , this is a PREAMP not a buffer , if you need a buffer , look to the TL072 based buffers like this one :
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An externally hosted image should be here but it was not working when we last tested it.
And yes , piezo's need way higher impedances then just 1M , my piezo mic required 10M to prevent loading
Hi to all,
That what doing Peter Sesselman looking interesting. Taking into account the three types of vibration on the piezoelectric element, may seem too complicated nature of the real effect of vibration forces applied to the three points of the piezo elements: center bottom, center top, and brass plate rim. Maybe is need to find what is widths of bottom and top contact points, but finally there are need experiments to see what and how really doing binding forces. I would not consider only "shaking" kind of forces, illogical because really do nothing alone.
By my experiments, conclusion is for sure that certain amount of pressure on the piezo element mounted on the favorable place of guitar resonator, give the optimal result. It consider most of all squeeze forces.
Also second nice thing for loud piezo output, is to use just double piezo element. You can find it in any cheap Chinese car piezo tweeters or PA piezo horn. Than match input impedance on the preamp, and look what nice signal you will get.
Good luck!
Peter
That what doing Peter Sesselman looking interesting. Taking into account the three types of vibration on the piezoelectric element, may seem too complicated nature of the real effect of vibration forces applied to the three points of the piezo elements: center bottom, center top, and brass plate rim. Maybe is need to find what is widths of bottom and top contact points, but finally there are need experiments to see what and how really doing binding forces. I would not consider only "shaking" kind of forces, illogical because really do nothing alone.
By my experiments, conclusion is for sure that certain amount of pressure on the piezo element mounted on the favorable place of guitar resonator, give the optimal result. It consider most of all squeeze forces.
Also second nice thing for loud piezo output, is to use just double piezo element. You can find it in any cheap Chinese car piezo tweeters or PA piezo horn. Than match input impedance on the preamp, and look what nice signal you will get.
Good luck!
Peter
And also , you can apply a weight for compressional forces , but there are limits .
Yes , a stronger compressional or torsional force = more bass ( think speaker excursion ) but never exceed some limits , and like speakers , more piezos = more power . Wire multiple piezos in series to reduce loading .( i might be wrong )
Yes , a stronger compressional or torsional force = more bass ( think speaker excursion ) but never exceed some limits , and like speakers , more piezos = more power . Wire multiple piezos in series to reduce loading .( i might be wrong )
I have a Dean Markley pickup that I've tried to use to detect speaker cabinet vibrations. Haven't had much luck, the output is low and bass shy. My M-Audio sound card has in input impedance of 220K with a gain of 40dB. It' very hard to get much signal over noise.
I have several piezo discs here ready to try. I'll post here if they give me better results.
I have several piezo discs here ready to try. I'll post here if they give me better results.
That's FAR too low an impedance, add a single FET source follower to the input to get a decent input impedance.
Yeah. I don't know why the instrument input would be 220K. I think a couple of my other cards have a 1M instrument input. Will have to try them.
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