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@Easypeasy found 2x more expensive ones but also without wired connector for a 2 pin header.

[USER=655016]@cupoftea[/USER] you said "i won't even bother with AC coupling of the signal.." is a big misteak   Since you have no idea exactly what IDSS is on the FET, nor the DC output bias voltage, any substantial DC gain will saturate the Op Amp to one DC rail or the other.

A more prudent design choice is to provide 20 to 26 dB gain between 1k and 4k with a 4th order BPF then detect peak amplitudes sustained for 1 second above 1Vpk.

This can all be done using a single quad OA with a logic level out. The detector ought to be an AC coupled diode-detected integrator with a suitable Vref.

i won't even bother with AC coupling of the signal..

No. It'll only be reliable to condition the signal to avoid false positives and true negatives.  (Although it might be possible to avoid the fault in the 1st place. It depends on the cost of failure)

[ATTACH=full]198330[/ATTACH]Use a (Vcc-1V)/2 for Vin+ ref on each stage for use on a single supply such as +5V on an LM324B.

The LM324B quad OA is cheap and has PNP inputs thus the Vin+ optimum is less than Vcc/2 and price is $0.053usd |  1u

The LM1369 quad OA is not cheap but is  R2R.

e.g. Mouser non-stocked

                   Quantity:      2,500 MOQ                               

                                   Unit Price                  $11.17

                                   Ext. Price             $27,925.00