Phone module for the Arrakis MARC-15.
The MARC-15 supports two phone modules for two external hybrids. Each phone module (caller) has its own mix-minus bus that includes the other phone module (other caller). The convenient Offline button switches the module so that the caller hears the console mic only. When not in off-line mode, the caller mix-minus is fed from a mix of the three output buses (Pgm, Aud, & Utl). Relay isolated logic control of the external hybrid is actuated by the module's on-off buttons.
