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Re: hydrophones

 

Well, after a massive delay I've managed to get my first board populated. I tested it with two identical piezo elements (as I've had no joy in sourcing cylinders in the UK yet).
One element went through the buffer and the other was routed through a HOSA MIT-129 impedance convertor I bought along with a JrF C series contact mic.
The difference between the two is astounding. And this is despite me completely missing the note about having C6&7 as close to the OPA pins as possible...
I had a bit of a mare assembling the boards as it seems the paste I have is EOL and despite thinning it with flux it was spitting and popping the passives off the board all the time. I'll have to wait for a new batch of paste before I can assemble more, as constantly finding where the tiny passives went was extremely annoying.

As a side note, is R10 the main element providing the Z matching? Is it worth playing with this value?
Another query relates to the elements used. I had some 15mm piezos that I had in a parts bin. Is it the size of these or the impedance that affects the sensitivity?

I'll post some wavs when I get to doing some more testing, but for now I'm waiting for the plasti dip that I dipped the element in to set.

On Mon, May 15, 2023, 13:32 Mark Day <neowalla@...> wrote:

[Edited Message Follows]

I was asking Adrian, but if you're working on this as well, great! I'll look forward to your build video and this new project.
By the way, I finally got a chance to test out my new hydrophones yesterday and no hum. After Mother's day lunch we went to the St Clair river below the Blue Water bridge and I managed to catch the freighter "American Spirit" as she headed up-bound into Lake Huron. I recorded the surface sound of the waves lashing the shoreline on two tracks, and the underwater sounds on another two tracks.
The hum is definitely gone now with this new set, but there are periodic pops and thumps which look like some kind of spike on the waveform. I manually removed them in Soundforge. Maybe just a property of piezo pickups.
I'll link to the audio when I get a chance.

IMG-20240321-WA0002~2.jpeg

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