The heart of the logic is a 6801 microprocessor and, unfortunately, this is not the kind of processor with an external EPROM, which could be removed to look at the code and perhaps on a good day change it. The GVG mixer was brilliant mixer in its day, but dated now. If we understand how the GVG panel works we can then investigate how to interface it to something else. The red bank of buttons controls the on air or PGM and the bottom white buttons are the PST or pre-set where the on-air source is previewed, before being switched to on air. The top set of 10 yellow buttons is the key bank. The GVG mixer can be controlled via this, using P2 protocol and there is a button on the panel to pass control to an edit controller. The communication from the panel to the crate uses RS 422, a standard that was extremely popular with linear edit suites. The cut buttons ordered as replacement items alone were over £30 each! They have a genuinely nice feel and can be customised by printing the source name onto an overhead projector gel, cutting, and fitting it inside the button. As the most expensive part of any mixer is the control surface being able to re-use an existing panel was a popular move. This was a brave move, as it enabled Ross to produce a very price competitive switcher. Later a separate company, Ross, designed and built an SDI (digital TV) mixer crate that again connected to the same control panel and used the same protocol. The control panel was able to drive either version. The crate first appeared as a small 3U unit that could mix composite video and was followed later by a larger crate that brought component mixing to the party. The two units were linked by a small cable carrying RS422 serial commands. The unit was in two halves, a crate which was rack mounted and an extremely attractive control surface housed in a desk top case. They then added a whole range of production switchers from the small to the very grand, but the small GVG-100 is the one that captured everyone’s imagination. In 1968 they introduced their first vision mixer, or production switcher as they are better known in the USA. Back in 1959, Grass Valley was born, a company that produced equipment for the television broadcast industry.

Vmix control surface diy