PURPLE MC77
Service Manual

6. BACK PANEL CONNECTIONS XLR Pin Assignments: PIN 1 = Chassis, Earth, Ground PIN 2 = Signal "Hot", Positive, ø+ PIN 3 = Signal "Cold", Negative, ø-

Wiring systems vary from facility to facility. PIN 1 may or may not be used to terminate a shield or drain wire. In general this pin and the shield or drain wires connected to it are not to be used to �Ground� or �Earth� the unit. Shields and Drain Wires should NOT carry current and are generally connected at only one end of any given wire. For your convenience and to assure that the chassis can be easily grounded (earthed) there is a Chassis Ground Lug on the back of the unit and the center pin of the IEC power inlet is connected to the chassis as well. PINS 2&3 of the input and output XLR connectors must be connected to get signal in and out of the unit. Since the inputs and outputs are transformer balanced there is no problem unbalancing either the input, the output or both. Because the input attenuator ahead of the input transformer takes PIN 3 of the input XLR to signal common is the preferred way to unbalance the input. To maintain consistent phase from input to output connection of PIN 3 to audio common is the preferred way to unbalance the output unless you WANT to flip the phase. Input & Output XLR: Standard connections - Transformer isolating. Insert Send & Return XLR: a differentially balanced send and return into the normal connection from the top of the output pot to the side chain detector and gain control circuitry. This loop allows EQ, filters and other external processors to be used to modify how the limiter responds i.e. as a vocal stressor or with a low cut filter to limit bass and improve its definition. This insert is always sending return is bypassed until activated. Stereo Interconnection: Two 1/4" Jacks marked Link, Input and Output are used to connect two units together for stereo mode utilizing the link control on the front panel. Using two 1/4� TS or TRS cables connect the Out jack on each unit to the In Jack on the other unit. IEC Power Inlet: Accepts standard IEC type power cable and includes: Fuse Holder - see back panel markings for fuse rating Audio & Chassis Ground: Audio ground is connected to the audio circuit, Chassis ground is connected directly to the steel case and the IEC ground. These are shipped from the factory linked, leave these linked unless you have a reason to separated your audio and chassis grounds. If you do separate them leave the link on one of the lugs, otherwise you will lose it.