2nd stage amplifires are power chips like TDA2030D ( http://akizukidenshi.com/download/ds/unisonic/TDA2030.pdf ), but I don't know it can be used as a voltage follower. It may need to use some resistors for the negative feedbacks without oscillations. And also become to need to use some capacitors as filters. Actually I cannot solve these until building circuit in real maybe.
In real, have to build 2 channel amplifires for stereo, and have to ajust these gains. Then I have to ajust gains of 4 operational amplifires.
