Preamplifier circuit for towing hydrophone array isn’t working

Thread Starter


Joined Aug 2, 2018


Joined Nov 29, 2005
If you have another AD743, try instead installing a 8 pin socket and complete soldering your project to the socket, keeping The IC in electrostatic-safe packaging until all done, then insert caring for ESD.
I do not like the circuit does not have counterparalleled diodes to clip the piezoelement spikes voltage.
I would implement such before inserting the new AD743 in its socket.
Is there a DPST switch to power on ?
The 3 'Gnd' board pins; are they hooked somewhere ?

And I do not understand the "Hydrophone elements never provide much output voltage" statement on the schematic.

And piezoelements must be mechanically held at the rim, do not use/test just on air hanging by its wires.
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Joined Feb 8, 2018
The first thing I would do is measure all of the In-use pins of the op amp relative to circuit common ("ground"). Pins 4 and 7 should have the appropriate supply voltages of course. The output and the two input pins should all be very close to the same DC voltage and within a few millivolts of zero (because of C1, the amplifier has a gain of 1 at DC and the only DC at the input should be due to "input offset voltage" of the amp, which should be in the low millivolts range, at most).
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Joined Feb 8, 2018
If the voltages look OK and you have another 10 µF or larger capacitor handy, try this:
- bridge the 10 µF across the C1 temporarily; this increases the gain at low frequency
- touch the input that would normally go to the transducer with a finger. This will couple AC mains "noise" into the input, unless your doing this well away from any AC power lines. The gain will be about 30-40 at mains frequency, so you should get a fairly large signal at the output. Be careful if you have the output connected to an audio amp - turn the amp down to avoid a loud rude surprise.

I'm assuming you are confident that your piezo transducer responds in the frequency range of interest.