In the circuit diagram on this page, there appears to be an unspecified op-amp. Could anyone guess at a component I could use for this and/or explain why there is no specification?
Background: I am mildly clueless about electronics. I want to build this piezo preamplifier,
which uses a pair of matched JFETs. It lists possibilities for special matched JFET components which do indeed seem to be difficult to source, and alternatively suggests single JFET components which would have to be matched by hand. It recommends the above page as instructions for JFET matching. I'm trying to figure out what components I should get if I go down the hand-matching route.
Side-questions: (Apologies if these are too numerous, please ignore at your convenience.) Can I build the matcher on a breadboard or will it be better to solder together? Given the purpose of the circuit I'm matching the JFETs for (eg. it's run off 48V phantom power, not a 9V battery) should I make any adjustments to the matching circuit (ie. use a voltage source other than 9V battery; a different Rset value)? Or can anyone recommend a matched JFET component available in the UK?