The approaches used in both the amplifier and supply power stages were cutting edge at the time. The amplifier was a linear design that used closed loop current cells to linearize MOSFET devices. These presented to the remaining circuit a linear, controlled gain voltage source around which the remaining circuitry and control loop was added. The advantage of this approach was the elimination of thermal effects which could throw off biasing as well as exquisite control of the entire signal path. Equally elegant was the single stage PFC supply which realized both PFC functionality and isolation in a single stage.
