I was recently given a couple of input transformers and monolithic TOA audio opamps salvaged from a TOA board. Is it possible to cobble these together and make an very primitive (lo-fi) API style mic preamplifier on the cheap? I have a 500 series lunch box with two open spaces and would love to have it fully loaded. The only problem is that I don't know where to begin. I know that Eisen Audio had a DIY 500 series kit a while ago but it was discontinued in 2010...
Any help would be highly appreciated!