I've been suggested this circuit as a good low-noise high gain piezoelectric transducer preamp (used to pick up really faint sounds in water).
It is nice because it includes a high pass filter (yet no AGC or a compressor, which would be useful for long recordings with equipment left in the field and later retrieved).
How would you add either AGC or a compressor?
It uses two 12V batteries. Could I use just one yet be able to give both + and – voltages?
Gain is set with R2 and R3. Could I replace both of them with a potentiometer to have variable gain?
The high pass frequency is set with R3 and C1. Could I replace the R3 with a potentiometer and add a switch to disable the filter when it isn't needed?
Since I would probably be building just one, I'd like to pick up the best IC for this use so that I can't later think about "I'd have implemented that other IC".
Both AD743 and AD797 are suggested in the diagram. AD743 lists a 2.9 nV/√Hz at 10 kHz while AD797 lists 0.9 nV/√Hz at 1 kHz.
Since I'd be using this in the 3-45 kHz range, does this mean that the AD743 has less signal distortion at upper frequencies (hence the reference to 10 kHz instead of 1 kHz), or are they equivalent?
Thank you
Allison
Best Answer
The AD743 will work down to supplies as low as +/- 5 volts so try using a mid-rail generator like this: -
All the ground points in your circuit go to the mid-rail point. Choose an op-amp that is low noise.
Replace R1 and R3 with just a single potentiometer - the junction of R1 and R3 is where the wiper goes.
I would just choose a bigger value for C1; after all you don't need it to work down to 0.000001 Hz do you!
Read the data sheets. Swings and roundabouts. Look at the noise graphs in the data sheets. It has nothing to do with distortion.
I would start by justifying that some non-linear process was justified so, over to you.