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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