Perpetuating the winning formula : the CA-S1 was part of small, transitional and Japan-only lineups, all more or less based on the CA-1010 bestseller.
Just below the top of these "mini-series" (descending from the "R", very similar to the originals, to the "S", "X" and much lower "G", "V" and "Z") was the S1 :
slightly downsized (no Class A, smaller PTs, less heatsinking) but upgraded some :
better componentry, high-Gm high-fT transistors, more elaborate circuits and tone controls, even better layouts and MC stages, lower impdance outputs and a novelty :
the Output Impedance control, the function of which you can find outlined in the diagrams accessible below.
The tag for the CA-S1 was "The Extravagant Pre-Main Amplifier". But it still was selling for less than the CA-2000 or CA-1000III !
Or : how to make just as good (or better) but for less money - the early 1980s were approaching fast.