On May 25, 2024, at 07:43, Domingo Riesco via groups.io <chumariesco@...> wrote:

?Thank you Zach! So good that you documented and share your knowledge and experience.

I'd like to try the FET buffer, I never built one but it seems simple as the guts of my electrets :). My 'PiP' is ca.11V through a 20K resistor, which provides 0.5mA; instead of the standard 2.5V through 2.2K that your circuit is based on. I might have to replace the 150ohm drain resistor with something higher or try other JFETs, no experience on that as I said. BTW, maybe you confused drain and source in your text description of circuit–it seems to me that the 150ohm is a source resistor and the drain resistor is 'inside the recorder' (counter-intuitive).

I like your take on ultrasonic piezo discs, for flatter response. I suppose that they should be as big as possible and the resonant frequency not that far beyond the audible spectrum, to keep them sensitive. Some are 50mm with resonance at 40kHz, but rated 35W :s so not sure how they would sound.

is also interesting, with a higher resonant frequency than the LOM but unfortunately half sensitive.

Cheers,
Domingo