Later addition to the 1976 Laboratory Standard Series and more compact than the contemporary AD8000.
The first stage employs only FETs in the first stage to avoid the signal/noise ratio be influenced by (high-) impedance fluctuations as would be the case with regular transistors.
A silicon steel plate shields entirely the enclosure while the input terminals are wired directly to the PCB with optimal earth point for perfect elimination of external inductance noise.
A ripple filter blocks AC fluctuations ; a constant-voltage power-supply with large capacitance decoupling circuit deal with the rest of the ps, after rectifying and regulation.
Gold-plated terminals, metal-film caps and resistors and precision pots are used.
Given the +20dB or +30dB level boost, a ten-second muting circuit is provided to block sound during on/off cycles and avoid repeatedly ruining those perfectly new replacement woofers of yore.
The bypass position lets you use a moving magnet cartridge... but why bother when moving coil is so good ?