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

Tuesday, August 4th, 2009 | Building Things, Electronics, field recording, Live Shows

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

August 7, 2009

These are some excellent projects that you got here. I would love to hear some samples of what these devices sound like if you are willing to share.


Leafcutter John
August 9, 2009

Hi Max, there are 4 sound samples at the end of my post. Maybe you missed them somehow? Or maybe your browser does not have flash?


Gold Panda
August 12, 2009

Wow! Since I already made the same contact mic to record a kalimba I may just go forth and hydrophone!

[…] Burton/John and his hydrophonic experiments (with a full how-to on making your own hydrophone) at leafcutterjohn.com, and on his canal-tour partner, Lisa Knapp, at myspace.com/lisaknappmusic. Info on their tour, […]

October 6, 2009

John! You Da Man!! Thanks For Opening My Eyes Even Wider (Hope They Dnt Fall Out 1 Day) And Introducing Me To This Quadrant Of The Sonic World. I’m Hearing & Learning So Many Fascinating Things Every Day! :))

Really Like The Look Of Your Max Patch Too, Will Give A Go One Day. Trying To Get My Head Round Microsound, Granular Synthesis @ The Mo On My Undergrad Course @ Brunel, London. And Damn!!… Love The Idea Of Capturing The Changing Soundscape Whilst Moving Up The Grand Union. Capturing The Underwater Sounds As Well As Above Water. Genius!!

Gutted I Missed It… Hope It Went Well!

[…] using a submersed hydrophone which was made by Leafcutter John from a discarded can of chick peas [see how to make your own here]. “Is that actual canal water?” shouts one audience member, dryly given the transparency of the […]

[…] the market on the stuff. [Leafcutter John] uses the hot goop as his water-proofer of choice when building an underwater microphone (also known as a hydrophone). By installing a couple of piezo elements on one lid of a tin can he […]

February 17, 2010

That rubber duck is surreal

February 17, 2010

greeat stuff! indeed that rubber duck mixed with the tinny quality of the mic really sounded like some old talky recordings. would be interesting to see how it can sound with an attempt to sing underwater.. find a pool or big enough sink?- or build two of these.. and use one as a speaker underwater, then the other to record the sweet underwater qualities of sound… well done

February 18, 2010

I almost wonder how well caulking would work for waterproofing (the kind of stuff you seal windows with). How has hot glue worked out for you?

Also, I notice you are hooking up two piezos in series, any reason for this? I thought it might be neat to put one piezo on each side of the can, and make a stereo hydrophone.

Leafcutter John
February 18, 2010

Yeah the rubber duck sounds a bit bonkers.

I reckon silicone sealant would work ok, but to be honest the hot glue worked really well. It is fairly cheap, is easy to handle, dries very quickly. The unit here has been submerged for hours and absolutely no problems so far. It’s worth noting that if the case is properly soldered the only place water can leak is through the cable entry so this area needs special attention.

I like the idea of singing underwater, will give it a try but i fear you’d have to let the water touch your vocal chords to get much to happen. Actually on second thoughts it sounds horrible, you try it and let me know if you survive.

Alex who designed the preamp has done lots of experimentation with different piezo configurations and suggested the dual arrangement to boost sensitivity, furthermore he suggests that you can add even numbers of piezos to form a long array which exhibit a figure eight polar pattern.

February 18, 2010

That’s really cool! I was wondering if a round Altoids Mint can might be easier to work with. Just screw it shut and blast some sealer around the edge. Or maybe one of those Kiwi Shoe Polish cans might work well, too.

Leafcutter John
February 18, 2010

The tin can is surprisingly easy to work with and the corrugations and folded end seams make it quite strong. I like the idea of using Kiwi Shoe Polish cans, you might have to make a smaller circuit to fit in there though – you could use surface mount devices maybe.

February 19, 2010

ei, you have a great idea, but you use a hot glue, my experience with hot glue and elements in wifi antennas is that hot glue don’t do it. try to use epoxi for wire hole and silicone for the mike inside. sorry for my english!

February 19, 2010

You can also fill the can with oil to compensate for buoyancy and maintain the effect of liquid sound transmission without shorting the electronics. I know of someone who found great success in using old 35mm film canisters filled with vegetable oil and quarter sticks of dynamite when seeking sound design sources for submarine explosions. Before the inclusion of the oil, he was having problems with blast compression. I’m sure that the rubber duck isn’t creating such issues though.

Whit Menzel
February 19, 2010

The best hydrophone i have ever made was also the simplest design i have come across, it requires a standard radio-shack electrolytic mic, some wire,a container of laxative(mineral oil) and a condom. No joke, you look like a real piece of work when your at the cash register but the results are amazing. first you hook up the mic as show on the box, plug it into your preferred amp to test it, next fill the condom with mineral oil and place your mic inside. tie it up and your ready to go. The mineral oil doesn’t conduct electricity so the electronics are safe, the oil also approximates the acoustic impedance of water this means that very little sound is reflected off the condom and you get a rich signal.

Leafcutter John
February 20, 2010

“you look like a real piece of work when your at the cash register” Hahahaha Great stuff! Might try this idea.

[…] > Swim and/or listen with the fishes with Leafcutter Johns DIY Hydrophone & Preamp […]

[…] Leafcutter’s DIY Steel Can Hydrophone & Preamp. Step-by-step guide | leafcutterjohn.com. […]

March 28, 2011

hi, have you a copy of the piezo pre amp schematic as the link is dead.

April 20, 2011

Hi, I’d love a copy of the schematic too, link is still down. Thanks

Stephen Harvey
May 29, 2011

Hi John, I keep trying the Alex Rice link but it has been dead for some time now. Would really love to try this project but cannot find another decent preamp schematic anywhere. (probably not looking hard enough!) Be great if you could post it up sometime. Thanks.

[…] for a DIY hydrophone for an upcoming project idea and have found this wonderful contraption by Leafcutter John!I’ve ordered most of the parts online but am trying to decipher part numbers for some of the […]

July 10, 2011

Hi again, I came across this link while researching ‘pre-amps’ and trying to locate the Alex Rice info… thought it might be of use to some of your readers – it has the pcb, and some helpful info! I’m currently trying to decipher the various part numbers for each of the components, and work out the schematic… but, its all getting a wee bit closer!! thanks again for such a great post!


August 23, 2011

If you use a can opener that cuts the lid seam rather than the lid, you can save yourself a little trouble. THe resulting lid fits almost watertight without glue or solder. If you carefully apply a continuous thin line of glue on the lid or can, it will be watertight.

Hydrophone recordings
August 31, 2011

[…] with a homebuilt hydrophone. Originally I intended to go for the extremely awesome hydrophone build Leafcutter John had made, but at the time the link to schematic didn’t work (though it should be up and […]

December 5, 2011

definitely making one of these! spent the weekend watching circuitry tutorials http://vimeo.com/electron this guy has lots of good ones.
I went to maplins to get the parts (not much luck!) Is there any place you got the parts, I looked for 3M resistors and they seem a bit hard to get. I am a newby to all this (and it will be first circuit ) so was unsure what I was looking for.
great how to thanks.

[…] Hydrophone: leafcutterjohn.com/?p=915 […]

[…] and a few less sticks of hot glue. I took my inspiration for this one from Leafcutter John’s Tin Can Hydrophone. It follows a similar principle and you could use practically any container to house to piezo […]

November 18, 2012

i looked at this project and thought: such a thing thing i want to build!
i didn’t have FETs at home, so i used an lm386 amplifier chip(i use this one for almost all small signal things :D) to preamplify the piezo, it works as well i think.
I don’t have steel cans at home, is it also possible to use tupperware or something like that, or does this sound bad?

Leafcutter John
November 18, 2012

Regarding the use of Tupperware – if you don’t send the hydrophone too deep in water then I think the tupperware will probably be ok. You’ll have to do some tests to see how much it gets squashed by the water pressure and you’ll have to work out how much weight to add to make it sink. I don’t know how it will sound but I’m guessing it’ll be fine. The reason I used a steel can was that it would be tough and I could seal it quite easily.

Let me know how you get on!

tyuytuytuytuyt - Page 371
December 11, 2012

[…] […]

[…] DIY hydrophone […]

Thank you for the good writeup. It actually was a entertainment
account it. Glance complex to more added agreeable from you!
By the way, how could we keep in touch?

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