I get it, it's a hobby project, but I feel the knowledge of analog electronics is getting lost in a way (and yes the analog people are the worse at explaining things - I think I saw YT videos more informative than whole university courses)
There were definitely well-known circuits for driving transducers, but I had to improvise to make a circuit small and simple enough to build 100 of them.
Building new circuits requires tinkering and many tries, regardless of the builder's knowledge.
Yes, maybe an Opamp that works at 40V could have worked (with an appropriate feedback config), but your end result looks ok. I'm just saying that putting the transducer in the emitter was a non-starter (as you correctly pointed out)
> Building new circuits requires tinkering and many tries, regardless of the builder's knowledge.
Absolutely, I'm not denying it :) It's a great job nonetheless
I don't get it. What do you mean by that?
But another reason (which would be valid for a resistive load as well) is that anything plugged into the emitter will have its impedance "reflected" to the base.
Even if you're talking about a digital circuit you need to think about transistor biasing. A pure capacitive load on the emitter means no biasing.
One of the ways you could work around this is to have an inductor in parallel with the transducer so it would resonate at the frequency you want https://en.wikipedia.org/wiki/LC_circuit (though not very practical to your case) - but ideally this would go on the collector, not on the emitter
Your 3 transistor solution is ok for the most part. Maybe it's doable with only one transistor but probably would need an inductor and/or wouldn't be too efficient.
(Not the best explanation, but this would require some trial and error and actually thinking a bit about the analog aspects of the circuit)