Tap on a ceramic capacitor or vibrate it with sounds and it produces a signal. Ceramic is similar to piezo material.
too bad i don't have any film caps, might find few if lucky.
Does the 1M 'scope probe have 240 ohms in series with it?
Yes, this is indeed the load now, just checked and there is 1M from scope and 240 ohms from probe in series loading the peak detector, so total is far more than only 240 ohms.
I used an MC33172 which might not be available anymore in a through holes package and might be in only a surface mount package now but there are many others.
I searched around and found ca3130, from what i understood, it works in single supply, slew-rate is faster, 10v/us (closed loop) 30v/us (open loop), compared to lm358's 0.6v/us (unity gain=closed loop?)
input offset voltage is quite close to 358's, 5mv max so not huge improvement there
And it seems ca3130 is rail-rail opamp, and applications say also peak detectors among
https://www.farnell.com/datasheets/31897.pdf
I did check also more up-to-date models from Ti, and there was at least some here, with much smaller input offset (around 250 microvolts or so & single supply) but with smaller slew rate, but, then again, that opamp you use has 2v/us so it could be overkill perhaps to use ca3130 as it has 10v/us.....
I compared mostly input offset and slewrate. And that opamps in question are single supply, rail-rail so no biasing is needed (at least on ground-side) and have at least 5v supply voltage , as lm3915 works well enought in 5v, at least it seemed to work and datasheet confirms it too. correct me if i'm wrong!
oh, and i checked your opamp as for market, there are at least surface mount models, sold around 0.6-1€/piece
and, one thing i really don't understand: what makes what opamp to need dual-supply, and what works well in single-supply? i know it is mentioned or shown in datasheets, but is it in internal-circuit diagram, or in electrical values-table?