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Old 23rd August 2011, 08:37 PM   #21
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by tinitus View Post
and what would be the result of lower impendance load ?
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.
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Old 23rd August 2011, 08:47 PM   #22
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Originally Posted by kevinkr View Post
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.
What sort of a circuit would you recommend? Could you give me a schematic?
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Old 23rd August 2011, 08:58 PM   #23
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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.

Last edited by wazupwiop; 23rd August 2011 at 09:01 PM.
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Old 24th August 2011, 03:26 PM   #24
TheGimp is offline TheGimp  United States
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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.
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Old 24th August 2011, 04:52 PM   #25
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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

Last edited by Michael Koster; 24th August 2011 at 04:57 PM.
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Old 24th August 2011, 05:16 PM   #26
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Quote:
Originally Posted by Michael Koster View Post
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
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!
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Old 24th August 2011, 08:05 PM   #27
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Configure it like an electret mic amp.
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Old 24th August 2011, 09:02 PM   #28
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Configure it like an electret mic amp.
Cool! I looked up some schematics. I will definitely try that.
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Last edited by wazupwiop; 24th August 2011 at 09:06 PM.
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Old 25th August 2011, 10:57 PM   #29
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My piezos still have not arrived. I will be heading out to take care of a family emergency. Will post when I have a chance to test.
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Old 30th August 2011, 11:29 AM   #30
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There was a hold-up at the factory. I am getting everything sorted out through e-mail.
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