* Ground loopsAC ground is provided to the RX-7 and all associated equipment, and this may cause an
increase in hum noise if care is not taken in connecting other equipment to the mixer. This is
because a ground loop is made through the shields of the connection cable and the AC line as
shown in Fig. 15, increasing hum noise. To solve this problem, either the chassis ground of the
signal line should be disconnected at either piece of equipment, or the chassis earth ground
should be disconnected, so that the ground loop is eliminated. This problem can not be easily
solved in the case of equipment connected to unbalanced signal lines. However, it is highly
dangerous to disconnect the AC ground, as microphone and other equipment connected to the
mixing console are often touched directly by the hand. This may cause an electric shock in the
case of electricity leakage, if any other connected equipment is touched. Therefore the chassis
ground line should be disconnected. Whether to disconnect the chassis ground line of eith er
piece of equipment depends on various conditions, therefore, they should be checked and
determined for each installation condition.
In the RX-7, a ground lift switch is provided on the balanced inputs and outputs with XLR type
connectors (excluding air monitor inputs and talkback input) to prevent ground loops.
This switch is ordinarily set to the NORMAL position, and should be set to the LIFT position
only when ground loops occur.
(Fig.
15)