piezo transducer signal amplification

I wish to use piezo transducer 273-073A to pick up and amplify insect activity. What kind of simple circuit would amplify enough for ear phones?

Reply to
desufnoc
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The gain will depend on how much noise you can tolerate.

Noise sources can be from induced EMI(ex:hydro lines), intrinsic transducer noise and intrinsic op amp noise... Possible power supply noise too..

Most basic would be to use an op amp circuit + head phone driver amp module. Something more advanced would probably be like a tape head amplifier circuit.

A circuit might pop up with some Goggling..

I don't know the transducer you're using but that part number reminds of Radio Shack numbers.

D from BC British Columbia Canada.

Reply to
D from BC

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Reply to
Martin Riddle

Oopps... Maybe I can rescue that.. How about? Goggling at Google. :)

Got some subs ideas... Googlizing... Googlization Googlyzing Googification

D from BC British Columbia Canada.

Reply to
D from BC

To understand piezo microphones, it's useful to think of a piece of ceramic, that's going to be flexed by an impinging sound wave. The first problem is that the acoustic impedance of ceramic is so much different than air that it'll not interact very well, and only a weak signal can be picked up that way. In fact, using Google, it appears this transducer is meant for use as a contact pickup, e.g. with a guitar, piano, etc.

Second, in case you do want to work with the piezo transducer anyway, to analyze its use, you only have to realize it appears to be a capacitor with its voltage signal in series. Resistive loads on capacitive sensors make a low-frequency rolloff, so to design your preamp you need to know the piezo capacitance and your desired low-frequency limit. For example, if the capacitance is 150pF (I didn't find the RS part's spec), and you wish it to work down to 50Hz, then the "load" will have to be above 22 meg-ohms. The answer is to use a JFET-type preamp and keep the necessary dc-bias resistor at 22M or higher. You can lookup JFET.

You'll want lots of gain, of course, but we can tell you the noise level will be determined by a parameter we call voltage noise, e_n, which is lowest for JFETs with a large die area.

There are JFET opamps that are pretty good, but discrete JFETs can do much better. If you look, you'll find lots written about the subject.

Reply to
Winfield

On Jan 19, 7:13 pm, Winfield wrote: [....]

If you need to go descrete:

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and look at the IF1801 JFET
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and look at the LSK170 You can also parallel JFETs to get better noise performance. The improvement goes as the sqrt() the number of JFETs.

Depending on the capacitance of the crystal, the current noise of the amplifier may also matter. The current noise times Xc gives an additional noise.

As op-amps go, the LT1169 may be about as good as you can do for low noise voltage and current.

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Reply to
MooseFET

The LT1169 is a nice amplifier, but it's got a rather small JFET die area, as evidenced by its capacitance, only 2pF. This shows, with its moderately-high noise spec, e_n = 6nV.

As we point out in AoE's lengthy low-noise chapter, optimum low-noise performance is had when a JFET's Ciss is near to the sensor's capacitance. Sadly, it's often hard to reach that goal. For example, no opamps are available with anything like 150pF of input capacitance, but one of the higher ones is Analog Device's AD743, which is 20pF and has e_n = 2.9nV, twice as good as the LT1169.

As for discrete parts, NXP's (Philips) bf862 at 10pF and 0.8nV is pretty good.

It's interesting that the bf862 JFET has half the capacitance of AD's fine JFET opamp, but instead of sqrt-2 more noise, it has 3.6x less noise. My suggestion, get a lifetime supply of bf862 JFETs.

Reply to
Winfield

Lifetime supply? Now please don't tell me that they rang the bell on that one ...

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

There are other JFETs out there:

The IF1801 is 100pF and 0.5nV/sqrt(Hz) The IF3601 is 300pF and 0.3nV/sqrt(Hz)

The LSK170 is 20pF and 2nV /sqrt(Hz)

The bf864 has the disadvantage that you can't find it on the NXP web site unless you know what to look for.

Reply to
MooseFET

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