Operating Instructions
①TO ELIMINATE HUM IF THE ABOVE HAS FAILED:
A)Disconnect the power from all outboard devices and tape machines except for the mixer and control room monitor power amp.
B)Plug in each tape machine and outboard effect device one at a time. If possible, flip the polarity of the plug of each device (turn it around in the socket) until the quietest position is found.
C)Make sure that all of the audio cables are in good working order. Cables with a detached ground wire will cause a very loud hum!!
D)Keep all cables as short as possible, especially in unbalanced circuits.
If these basic experiments don’t uncover the source of the problem, consult your dealer or a technician trained in proper studio grounding techniques. In some cases, a “star grounding” scheme must be used, with the mixer at the center of the star providing the shield ground on telescoping shields, which do NOT connect to the chassis ground of other equipment in the system.
Note that the Multimix 12R is grounded through its AC cable. Signal ground is connected to chassis ground, which in turn may be grounded again by the rack rails. But since almost all of the inputs and outputs of the Multimix 12R are balanced, the ground does not have to be made part of the signal path unless you are connecting to unbalanced equipment. If the Multimix 12R is mounted in a metal rack, the mixer shares a common ground with the other equipment in the same rack. In some cases (such as a star ground scheme), you may need to use nonconductive rack rails or rack isolators to avoid ground loops.
To avoid the possibility of electric shock, never defeat the safety ground found on other equipment in the system. When in doubt about proper electrical grounding schemes or the power to your system, consult a qualified, licensed electrician.
Telescoping shield: In fixed installations using balanced outputs where the amplifier is more than 20' from the mixer and on a different AC power panel, it may be advisable to disconnect (or "float") the shield at the amplifier end. This keeps the ground potential of the amp