Piezoelectricity

Shit I’m a Geek / The joy of Piezoelectricity

Sunday, July 26th, 2009 | Building Things, Electronics | 16 Comments

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.

 

amazing!

amazing!

Take care!

Leafcutter John x.

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