These are the scans of the VCA Installation Manual pages which are part of the OPTIFILE TETRA User Manual from 1994. These pages were not included in some later versions of the manual. I also have the original disk with Utility 1.2 software which is necessary for adjusting correct VCA gain (see pages 9-12). However, I did not found yet a disk drive which would read the 720k floppy disk. As soon as I find it I'll post the software on this page.

As a curiosity I added my own shematics of the VCA board and 3 optional switches which control individual console channel Status, Mute and VCA bypass (see the picture here). I have added some logic circuitry which toggles each function on and off.VCA bypass works independently from the Optifile computer and can be Set/Reset globaly for all channels. Digital and analog grounds need to be separated here which was accomplished by an additional relay.