Shit I’m a Geek / The joy of Piezoelectricity

Sunday, July 26th, 2009 | Building Things, Electronics

For some reason I have become completely obsessed with electronic circuits in the last couple of weeks. Maybe it’s because I bought a semi-decent soldering iron for the first time and realised that it’s very satisfying to make nice shiny connections. I think i’m headed toward a life breathing in the heady (and no doubt toxic) vapor of solder fumes.

Anyway I know next to nothing about building electronic circuits so it’s been a bit of a challenge to pick up the basics. I’ve been studying Ohms’ Law, and working out how to interpret circuit diagrams, while I was looking for information about audio circuits I stumbled on an interesting first project.

Introducing Alex Rice’s Piezo Preamplifier

If you click on the link you’ll find a schematic and lot’s of notes on component selection and construction and interesting information on how the circuit actually works. I must say that I don’t understand all of it but I thought it looked like a useful circuit to have.

First a little about Piezo discs….

£0.14p Piezo Disc - attach a jack lead and you have a Contact Pickup!

Piezo discs are fantastically cheap and interesting things, they are like sonic microscopes and allow you to to make very simple ‘contact pickups’ which can be pressed onto objects to probe for hidden sounds. I have used them constantly since I discovered them about 10 years ago. I used them a lot to record mechanical sounds for my 2003 record Microcontact. Here a Zip disk gives way to a mechanical breast pump…


if it sounds half as good as it looks.....

Looks like this....

Sounds like this….

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Over the years I have used piezo discs to:


In a hydrophone....

listen underwater....


record the slinky...

record the slinky...


and hear ice melting.

and hear sound of ice melting.

Brilliant as Piezo’s are my interest in them had started to wane a little in the last couple of years. Things recorded using them tend to lack bass and often sound a bit thin. Alex’s Circuit addresses the problem of impedance matching the Piezo disc and the audio input (which helps counter bass loss). He also promises ‘to make piezo contact microphones sound awesome’ which has to be worth a go!

Alex’s circuit is very simple with just 12 components but given my complete lack of knowledge in this area it took me a couple of days to make sure I knew which were the right components to get. I ordered from Rapid and true to their name the parts arrived in a few days. I first tried to build the circuit on a proto-board which allows you to prototype circuits without soldering. When tested the first version it was very noisy and had a lot of 50hz hum. I had another shot at the circuit and because I was finding it hard get my head around translating the schematic to the the proto-board got very confused indeed. I decided to have a break and then take the plunge and solder the parts onto breadboard figuring that it might sound better as the components would be better connected. After a hour or two I had this:

Phantom powered piezo pre-amp

My first circuit - Phantom powered piezo pre-amp

Thankfully again it failed to explode and sounded much better on the bread board. There was still some hum and interference which went away when I shielded the board using a little metal tin box.

Here is a recording made with the Piezo stuck onto a Kalimba

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And one of my watch ticking (very quietly)

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The pre-amp sounds pretty good, amazing really considering the components excluding cable and XLR connector cost under £2.00. The recordings with the pre-amp sound much fuller than without and I’m sure the noise you can hear in the watch recording would be reduced if I had matched the FETs as it says you should in Alex’s instructions.

I’m really pleased with my first circuit and have learned a lot. I wonder what I should try and build next?

before I go here are some links that I have been using to learn about electronics.

Alex’s Site has disappeared but his preamp remains!

All About Circuits

Java Circuit Simulator

And before I go have a look at Alex’s miniaturised  Piezo preamp which fits inside an XLR plug. It must be 1/6th the size of mine.




Take care!

Leafcutter John x.

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16 Comments to Shit I’m a Geek / The joy of Piezoelectricity

July 26, 2009

Great idea. Been using cheap piezoes in various cheap instruments, ukuleles and the Bogdon Box bass

Guess there is less of a need to buy those expensive transducers like

Thanks. Now to see if I can solder without burning my fingers off.

Alexander Rice
July 27, 2009

I’m glad you found my circuit useful.

I’m not totally sure what the source of the background noise in you watch recording is, it may simply be that the signal from the watch was very small and needed a lot of gain so the noise is from the pre-amp in your mixer/recorder.

The main thing that causes the piezo-pre to make noise like that is too much/little current through the current source — i found about 0.5 – 0.7 mA was best, much below that and it starts to get noticeably noisier; much above 1.5mA and the voltage from the phantom power will start to droop. Experiment by replacing R3 with a 2k potentiometer, adjust the pot for least noise and then replace it with a fixed resistor of similar value.

I’ll also let you in on a bit of a secret. There are two piezos inside each of my microphones, they’re both glued side by side to a strip of metal, connected in series with one having it’s + wire connected to ground and the other having the – wire connected to ground. The effect is to significantly boost the sensitivity of the microphone. Both piezos have to be electrically isolated from the grounded metal strip.

Another hint is that the wire itself can be a source of noise. Try hitting a section of cable — you’ll find that it is microphonic. I try and keep the distance between the piezo and it’s pre-amp nice and short which is easy with a phantom powered preamp.

[…] on a canal boat soon so I wanted to make myself a new hydrophone which includes the pre-amp I made here. I have made hydrophones using piezo elements before but I never tried using a pre-amp which tends […]

October 29, 2009


Don’t suppose you have a copy of the schematic for the preamp? Alex’s site appears to be down…

Leafcutter John
October 29, 2009

Oh no, the site has gone!

There are plenty of circuits suitable for this project on the web. Try looking HERE. There are links at the bottom of the page for two easy to build buffer/amps. These circuits are not phantom powered though – I’ll see what i can do to get the original schematic up here.

December 16, 2009

hello John, i’m really interested in building the tin can piezo hydrophone with pre amp but i have no idea on what components i need to purchase in order to build the circuit…

would you mind sending me a shopping list by any chance???


Leafcutter John
December 16, 2009

Alex’s site is back up now so you should find all you need to know here:

Good Luck!


December 24, 2010

Alex’s site is down once again. Do you have the schematic for this project?

December 25, 2010

Theres a good explanantion as to the bass loss & how to solve it, with a circuit diagram (its an impedance matching issue)

I gave away some of my contact mic recordings as a xmas present, have a listen/download here:

July 5, 2011

hi john, fascinated by your diy hydrophone and am going to make it my *first* project! i’m wanting to order the bits online for both the pre-amp, and the hydrophone – any chance you have a copy of the parts list + some basic instructions/doodles, i’ve checked the site you link to but it seems to be down, cheers!

Leafcutter John
July 6, 2011

Hello everyone, you’ll be glad to know that someone has started a page with the full details of alex’s preamp. The new link is in my post. If you want to go there now:

[…] from Leafcutter John: Leafcutter’s DIY Steel Can Hydrophone & Preamp. Step-by-step guide Shit I’m a Geek / The joy of Piezoelectricity [good background on the […]

September 11, 2011

Hi John,

I have a question regarding the resistor R3 in the preamp diagram. It says 1-2K. Is this the same as 1.2K (1.2000 ohms)or does it mean that R3 could be 1K or 2K? Thanks a lot. Great info and thanks for sharing it. Best, james.

Leafcutter John
September 11, 2011

Honestly I’m not sure, It’s Alex’s diagram. I imagine it means anywhere between 1k and 2k, or tune to taste maybe. If it’s a typo then 1.2k I doubt you’ll blow anything up by selecting a 1.2k resistor here. If you test the circuit on protoboard you can change the value and see what happens.

September 25, 2011

Thanks John.
and please regarding Q3, if I use two 2N3819 for Q1 and Q2, which part list would be Q3?
regards, james

[…] making my own, here are some links that helped my decide. Social sound design furious contact mic assemble” This entry was posted in work by richbate. Bookmark the […]

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