Thanks so much. ?
Yes, as you probably noticed above, there is a link to the 142PC schematic. What's missing is the illusive identity of the Q1 FET and the Q11 BJT. What they actually are probably doesn't matter, but their characteristics are important in choosing a replacement part. Similar products seem to use a 2N3819 or a 2N4860 for Q1. But, I don't quite understand the protection circuit: I'm guessing that when current? (or is it voltage?) exceed a certain level Q11 dumps it too ground to protect in input of the FET (Q1).
As I mention, there is a knowledge gap in my understanding of transistor amps/building blocks. This is actually a good opportunity to learn more about that - I'll pull out the textbooks. I guess OpAmps have made us a bit lazy. I unstained the basic opamp based CSA but I struggle with these diagrams to identify which components make up what is effectively an opamp. I think one of them delineates it and also identifies a buffer circuit.?
I know that we're diverging a bit from XRF proper into the hardware realm, but I'm a great believer in DIY hardware since it makes, otherwise expensive hobbies, accessible to the newcomer. (See for example the CERN Particle Detector project:?) Could you imagine if basic XRF technology was accessible to the amateur for under $100-200. I guess Theremino does that to some degree. But I have a (perhaps unreasonable dream) that one day a kit could be put together using an off the shelf SiPIN that with decent energy resolution, whereby a tinkerer could actually build a decent semiconductor XRF system for a few hundred dollars with a faster ADC than a sound card offers. Perhaps it could be a board that interfaces with the GreatFET ().
Now I need to go read Geo's paper.
Thanks,
Soren
