Here is the draft of my schematic:
The circuit proposes to use a TL741 op amp. This op amp has a null set function.
Here is what I read about null set:
Here is what I think that means:
If you are using the 741 as a buffer to fix the GND/0/Null rail to absolute zero (meaning the non-inverting and the inverting inputs are tied to GND/0/Null, set a trimmer between pins 1 and 5, with the wiper tied to the Negative rail.
My circuit does not use the op amp as this type of a buffer. Meaning, my inputs are not tied to the same (GND/0/Null) rail... They are referenced to different rails.
However, I do want the ability to set the GND/0/Null output to exactly absolute zero (as close as r-e-a-s-o-n-a-b-l-y possible.) The circuit includes a separate trim pot (RV3) to accomplish that.
So. for my education, as well as for use in this circuit... Is there a way to use the op amp's null set function with two different references? If so, how is that set up? If not, how best to terminate the null set pins?
Asides
1) Should I add D1 to the circuit, to account for any back inductance voltage? I used poor terms, here; my apologies.
2) The Power BJT Transistor I propose to use is the MJ4502G. See the data sheet, below. It is described as for Audio use, as opposed to General Purpose use. It appears to have all the specs that I need. Is there any reason to not use it, in this application?
Thank you for your help!