3-stage IC-based. Continuously variable gain from 30dB to 70dB. Input loading pluggable: > 47pF and <>AC-coupled with just one series capacitor, and this enclosed in a feedback loop at that. Resistors matched to 0.2%, capacitors to <>Takes bi-phase AC or DC power in, through rectifier, gyrators, and then opamp-based series regulator with multi-loop feedback. i found this on a site called vinyl engine. i didn't create this , some genius did. props to geniuses.