Leafcutter’s DIY Steel Can Hydrophone & Preamp. Step-by-step guide *schematic link fixed!*

*schematic link fixed!*

Completed steel can hydrophone

Completed steel can hydrophone

Hydrophones enable us to record underwater, this is reason enough to worship and adore them. Better still you can make your own very easily and cheaply. I’m going to be doing a musical tour with Lisa Knapp 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 to make piezo’s sound a lot better.

If you don’t know what the hell I’m talking about right now have a look at these instructions on how to make the simplest possible contact mic It’s exactly the same principle when making a hydrophone except you get to go underwater.

I decided to house the pre-amp in the same enclosure as piezo elements (to avoid noise entering the circuit). The challenge here is to find a decent enclosure. As the piezo’s and the pre-amp will be underwater they need to be inside something water-tight. I was thinking about building a little Perspex box to put everything inside but it quickly became apparent that my handsaw skills were not up to the job. After having some delicious spicy cheak-pea and tomato soup I thought it would probably be possible to solder up some kind of tin-can casing which would be fairly strong and water-tight.

Two steel cans cut down to size

Two steel cans cut down to size

After a few experiments, I found you can quite easily solder steel food cans together using a regular soldering iron and electrical solder. It works for water pipes so It should be water-tight in this case.  NOTE: aluminum cans will not work at all well!!! Get out your magnet and find some steel ones!

I used a small rotary cutting wheel on a dremel tool to cut nice neat slices of can. I then lightly sanded the ends totally flat. As you can see from the photo above I used two different can’s one with a clear coating and one with a white coating, these coatings need to be removed in the places you want to solder, it’s probably easier to do this now than later when you have installed the guts.

Piezo elements super-glued to lid and wired up

Piezo elements super-glued to lid and wired up

I used a wire brush to rough up the surface of the can before super-gluing two piezo elements to the inside of the lid. This design has a ground wire (yellow) soldered to the can lid. The super-glue insulates the brass parts of the piezo’s from the lid. You can’t see very well from the photo but the two piezo’s have had a straight edge cut off them so they fit onto the lid. They also have a small gap between them – they are NOT touching!

Piezo's coated in copious amounts of hot-glue

Piezo covered in copious amounts of hot-glue

I went out and bought a hot-glue-gun for this bit, and it was worth it. The glue eliminates any possibility of the pre-amp circuit shorting out on the piezo elements. It also protects the piezo’s if water should get into the capsule.

Tiny steel chimney

Tiny steel chimney

I drilled a hole in the larger of the two cans just big enough for my microphone cable to go through. Then made this little chimney out of a scrap piece of can. I used a wire brush to clean the coating off the can before soldering.

Chimney soldered onto can.

Chimney soldered onto can.

To hold the chimney into position while soldering I temporarily bolted it to the can. A few moments later and it looks like some kind of improvised smoking device.


Mic lead glued in position

Mic lead glued in position

I coated the mic cable with hot glue and pulled it through the chimney, then splurged lot’s more glue where the wires emerge into the can. This is the most likely place water will try to enter the capsule so make sure you seal it completely using ridiculous amounts of hot glue!


Pre-amp connected to Piezo leads

Pre-amp connected to Piezo leads

This shows the pre-amp connected to (and sitting atop) the piezo / hot-glue sandwich. For full details of the circuit see Alex Rice’s excellent phantom powered Piezo Preamplifier page.

Alex has been really generous helping me out with ideas to improve my pre-amp build and the dual-piezo idea came from him – Thank you Alex!

You do not have to use a pre-amp with this design, if you don’t want to build one just connect the yellow ground wire from the piezo’s to pin one (ground) on your XLR ended mic cable. Then connect the other red cable to pin 2 and the black cable to pin 3 (it does not really matter which way around these two go). That said if you don’t use a pre-amp you might be better off going for a simpler enclosure like this one.

Preamp connected to mic lead

Preamp connected to mic lead

All leads soldered-up! It was really fiddly to do and I made a wrong connection initially which was easily fixed. It’s a very good idea to connect your hydrophone to a mixer and check it actually works before you close the case.

I always write a  special message inside the casing of my hydrophones, and I suggest you do the same because It definitely makes them work better. This time my girlfriend added a message too so I’m sure this one is going to sound amazing!

Before closing the unit I covered the pre-amp circuit with a lot of hot-glue to seal it off from any stray water. I forgot to take a photo but by the end the can was almost filled it with hot-glue and coins (ballast)  to make sure it will sink and not float when it is put in the water.

Completed steel can hydrophone

Completed steel can hydrophone

My girlfriend bravely held the two halves of the case closed as I carefully soldered around the seam. Again I used a steel brush to clean the surfaces before soldering. It was actually quite easy to do and I like the quasi-welded appearance. All that is left to do now is pop it in the sink and test it out.

Fizzy bath-bomb

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Underwater Comb

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Submerged rubber duck

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Running Taps

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It took half a day to make the case and the same to make the pre-amp. The whole thing cost less than £10 in parts and compares very well against hydrophones costing 10 x the price.

I’m going to paint and varnish the casing, this is important if you don’t want your hydrophone to rust away.

Let me know if you build one of these or if i have left out any important info.

Go forth and hydrophone!

Leafcutter x.

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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.




Take care!

Leafcutter John x.

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Gigs this weekend and project Updates.

Sunday, June 14th, 2009 | Forester, Graphic Scores, Live Shows, Software News | 1 Comment


I’ve been super busy the last few weeks hence the complete lack of posts here. I have a couple of gigs coming up this week (sat/sun) which I’d like to let you know about. I’m also involved in some great projects at the moment which i’d like to share.

1. The first gig – Sat 20th June – is at the Cross Kings Pub, York Way, London N1 0AX. I’ll be doing some new tunes, old ones and some improv bits. Also playing: Liberez, Benjamin Wetherill & the Trumpets of Death, B¿Layachi Cousins Duo. Cost:£6, adv £5 

2. The second gig – Sun 21st June – is an early one 6:00 > 7:00pm, Royal Festival Hall ballroom, London. This event is on the closing day of Meltdown 2009 and is before this years curator Ornette Coleman takes to the stage. I’m really looking forward to this, I have managed to get a group of amazing musicians together to play some of my animated graphic score pieces. We’ll be premiering a new one where the audience suggest words and phrases which will make up the score. It’s a free gig too! 

3. I just finished a BBC commission for Radio 3, I was asked to work with Shetland poet Jen Hadfield on a new work. I’m not sure exactly when it airs but i’ll let you know when I do. It should be available to stream from the BBC website so you can have a listen even if you miss the original airing. 

4. I have spent some very pleasurable days with my friend Tom Haines playing about with hydrophones in a little pink paddling pool. We are working on a new piece which will actually be performed (and listened to)  in a public swimming pool using an underwater sound system combined with a regular air speakers.

Paddling pool, hydrophones, and sound objects

Paddling pool, hydrophones, and sound objects

If you want to come and experience the first and probably only performance of this piece it will take place on July 22nd at Clissold swimming pool 63 Clissold Road,London, N16 9EX. Bring your swimsuit! More Info.

5. Last but not least I have been tinkering with Forester II and have come up with the beginning of a lovely new interface. Here you can see audio files rendered as circles.




I’m still some way off having finished software for you so please be patient. 

See some of you this weekend!

take care,

Leafcutter John x.

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