User manual YAMAHA PM4000

[. . . ] PROFESSIONAL AUDIO MIXING CONSOLE PM4000 OPERATING MANUAL YAMAHA PM4000 OPERATING MANUAL IMPORTANT NOTICE FOR THE UNITED KINGDOM Connecting the Plug and Cord WARNING : THIS APPARATUS MUST BE EARTHED IMPORTANT. The wires in this mains lead are coloured in accordance with the following code: : EARTH GREEN-AND-YELLOW : NEUTRAL BLUE : LIVE BROWN As the colours of the wires in the mains lead of this apparatus may not correspond with the coloured markings identifying the terminals in your plug proceed as follows: The wire which is coloured GREEN-AND-YELLOW must be connected to the terminal in the plug which is marked by the letter E or by the safety earth symbol or coloured GREEN or GREEN-AND-YELLOW. The wire which is coloured BLUE must be connected to the terminal which is marked with the letter N or coloured BLACK. The wire which is coloured BROWN must be connected to the terminal which is marked with the letter L or coloured RED. * This applies only to products distributed by YAMAHA - KEMBLE MUSIC (U. K. ) LTD. Professional audio mixing console Typ : PM4000 82/499/EWG YAMAHA Europa GmbH MICROPHONE CABLES AND MICROPHONES CONNECTION TO PREVENT HAZARD OR DAMAGE, ENSURE THAT ONLY MICROPHONE CABLES AND MICROPHONES DESIGNED TO THE IEC268-15A STANDARD ARE CONNECTED. This product complies with the radio frequency interference requirements of the Council Directive 82/499/EEC and/or 87/308/EEC. YAMAHA CORPORATION How to Use This Manual If you are an engineer or technician who is familiar with sound system design, much of this manual will serve as a review for you. [. . . ] By completing the circuit between them, the performer gets zapped. Good grounding practice seeks to control such potential differences for the comfort and longevity of all concerned. experienced audio engineers. Sometimes, in poorly designed sound equipment (which sometimes includes expensive sound equipment), ground loops occur inside the chassis even though the equipment has balanced inputs and outputs. In this instance, little can be done to get rid of the hum short of having a skilled audio engineer redesign the ground wiring inside. It's better to avoid this kind of equipment. It is also best to avoid unbalanced equipment in professional sound systems (unless the equipment is all going to be very close together, connected to the same leg of the AC service, and not subject to high hum fields). If all connections are balanced and the equipment is properly designed and constructed, such ground loops will not induce noise. Unfortunately, much of the socalled professional sound equipment sold today is not properly grounded internally, so system-created ground loops can create very real problems. Figure 4-5 shows a typical ground loop situation. Two interconnected pieces of equipment are plugged into grounded AC outlets at separate locations, and signal ground is connected to earth in each of them. The earth ground path and duplicate signal ground path form a loop which can pick up interference. Normally, this kind of ground loop should not cause any noise in the audio circuits if (a) the circuits are truly balanced or floating, and (b) the audio common is maintained separately from the chassis ground within the equip- 4. 3. 2 Ground Loops AC line-frequency hum is, without question, the single most common problem in sound systems, and the most common cause of hum is ground loops. A ground loop occurs when there is more than one ground connection path between two pieces of equipment. The duplicate ground paths form the equivalent of a loop antenna which very efficiently picks up interference currents, which are transformed by lead resistance into voltage fluctuations. As a consequence, the reference in the system is no longer a stable potential, so signals ride on the interference. Ground loops often are difficult to isolate, even for Figure 4-5. Formation of Ground Loops Key for Figure 4-5 through 4-10 Page 4-6 ment. If one of these conditions is not met, then instead of going directly to earth ground and disappearing, these circulating ground loop noise currents (which act like signals) travel along paths that are not intended to carry signals. The currents, in turn, modulate the potential of the signal-carrying wiring (they are superimposed on the audio), producing hum and noise voltages that cannot easily be separated from program signals by the affected equipment. The noise is thus amplified along with the program material. Multiple-Point Grounding disappear unpredictably as pieces of equipment are inserted or removed. When they appear, problems are very difficult to isolate and fix. [. . . ] The affected input channel(s) have MUTE assign switches engaged, and the MASTER MUTE group to which the channel(s) is assigned is set to mute mode. The affected input channel(s) have MUTE assign switches engaged, and the remote VCA/MUTE connection is causing the MASTER MUTE group to be engaged. Disconnect the VCA/MUTE connector to check theory; if output is restored, check remote circuitry. Certain input channels or groups of channels, cannot be heard at Group, Stereo, Post-Fader Aux sends, or Matrix outputs. The affected input channel(s) have VCA assign switches engaged, and the VCA Master Fader to which the channel(s) is assigned is set to minimum level (down). The affected input channel(s) have VCA assign switches engaged, and the remote VCA/MUTE connection is causing the VCA Master level to go to minimum. Disengage VCA assign switch on the channel affected or raise the VCA Master Fader to a higher setting. Disconnect the VCA/MUTE connector to check theory; if output is restored, check remote circuitry. Certain input channels or groups of channels cannot be heard at Group outputs, Group-to-Stereo outputs or Group to-Mtrx outputs. [. . . ]