This is a rather unique Alembic Series II from 1979, one of the most collectable Alembics. Not only is this one rare - it is very special, because it is exactly THE ONE that Alembic pictured in their catalogue at that time !!!!
The guitar has the powerbox and multi pin cable. The Series II controls are master volume pickup selector switch, neck pickup volume, neck pickup filter, neck CVQ control, bridge pickup volume, bridge pickup filter, and bridge CVQ control. The master volume controls the output of the entire system. The selector switch chooses between neck pickup, both pickups, bridge pickup, and standby. Basically, the filter control is a low pass filter; as you roll it back it lowers the point at which it passes low frequency signals and blocks high frequency signals.