Shure m268 owners manual

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Outputs Dimensions See Figure 1 Noise Equivalent input noise: - 128 dBV (lo imp mic 150 ohms-300-20,000 Hz) at full gain OUTPUT Lo Imp Mic HI Imp MIC Aux Mix Bus Equivalent input hum and noise: - 125 dBV (lo imp mic 150 ohms-20-20,000 Hz) at full gain Output noise: -90 dBV (master control down), -65 dBV (master up) (input controls down, 300-20,000 HZ) Output hum and noise: -82 dBV (master down), -60 dBV (master up) (input controls down, 20-20,000 HZ) Output Clipping Level - 20 dBV (100 mV) + 4.5 dBV (1.7V) + 17 dBV (7.1V) -8 dBV (0.4V) IMPEDANCE Common-Mode Rejection 65 dB minimum with 100 mV input at 100 Hz Designed for use with Any lo imp (19 to 600 ohms) mic c~rcuit Unbal 10 to 50 kilohms mic circuit 10 kilohm or greater unbal high-level circuits 3.3 kilohms Control Interaction Less than 1 dB with any control combination Actual (Internal) 50 ohms 5 kilohms 2.2 kilohms 3.3 kflohms Phase All microphone inputs and outputs and mix bus are in phase; aux input is in phase with aux output, but out of phase with pin 3 of mic connectors Simplex Power 30 Vdc open circuit, 3.3 kilohms series resistance Operating Voltage Ac operation M268: 105-125 volts, 50160 HZ, 5W M268E: 210-250 volts, 50160 HZ, 5Wt Dc operation A2688 Battery Power Supply (optional ac- cessory): 27 volts nominal at 12.2 mA typical no-signal, 12.5 mA typical full output; 16.2 volts minimum; approximately 40 hours battery life with alkaline batteries, 4 hourslday duty cycle, simplex off External power: 30 Vdc, 12.6 mA no-signal, 12.8 mA full output Temperature Range Operating: - 18O to 57OC (0° to 135OF) Storage: - 29O to 74OC (- 20° to 165OF) t Can be rewired for 105-125 Vac operation (see Service section) 2 OVERALL DIMENSIONS FIGURE 1 Weight Net: 1.9 kg (4 Ib 2 oz) Packaged: 2.8 kg (6 Ib 2 oz) Certifications M268 (only): Listed by Underwriters' Laboratories, Inc. and listed by Canadian Standards Association as Certified CONTROLS AND CONNECTORS I WARNING I This apparatus must be earthed (grounded)! The M268 power supply is energized when the unit is connected to an ac source; disconnect mains (power) plug from supply when not in use. Model M268E Model M268E is supplied with a three-conductor power-line cord without a plug. The plug should be in- stalled by qualified service personnel. The brown lead should be connected to the "live" or "hot" terminal of the plug, and the blue lead to the neutral terminal. The greenlyellow lead is the grounding conductor and should be connected to the ground or earth terminal of the plug. Inputs A maximum of four low- or high-impedance dynamic, ribbon or condenser microphones can be connected to receptacles marked MIC 1, MIC 2, MIC 3 and MIC 4. The inputs are designed for low-impedance microphones with 19 to 600 ohms impedance or high-impedance microphones. Both low- and high-impedance microphones can be used simultaneously. Crystal or ceramic microphones are not recommended. Im- pedance is selected by a slide switch above each input. The input receptacles are professional three-socket audio connectors.* See Figure 2 for low- and high- impedance connections to inputs. Note that some con- denser microphones produce very high output signals which may overload the inputs of many mixers; the M268's feedback-type active gain controls virtually eliminate the need for in-line attenuators to compen- sate for these "hot" microphones. ' Designed to mate with Cannon XL series, Switchcraft A3 (Q.G.) series or equivalent connector.

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The rear-panel phono jack marked AUX IN will accept adversely affected by this interconnection. Mix bus in- output from a high-impedance, high-level source such terconnection can also be made with other Shure mix- as a tape recorder or am-fm tuner. ers such as the M267 and SE30. SHIELD SHIELD MICROPHONE MIXER INPUT MICROPHONE MIXER INPUT LOW IMPEDANCE HIGH IMPEDANCE (BALANCED LINE 1 MICROPHONE INPUT CONNECTIONS SHIELD -----7 SHIELD- - - - - - - - /, . - I \------A/ MIC OUTPUT MIC OUTPUT LOW IMPEDANCE HIGH IMPEDANCE (BALANCED LINE ) MICROPHONE OUTPUT PLUG CONNECTIONS FIGURE 2 Outputs The connector marked MIC OUTPUT is a dual- impedance output selected by the switch above the con- nector. This output is the "mixed" output of all the input sources and is designed to work into a balanced or un- balanced 25- to 600-ohm microphone line or into a high- impedance unbalanced amplifier or tape recorder microphone input. The connector is a professional three-pin audio connector.* See Figure 2 for output con- nector configurations. The phono jack marked AUX OUT is a high- impedance, high-level, unbalanced output designed primarily to feed a power amplifier requiring 0.1 to 2 volts input, or the auxiliary or tuner input of an amplifier or tape recorder. This output will also drive the input of a Shure Model M63 AUDIO MASTERQ. Interconnecting cables should be limited to a maximum length of about 25m (75 ft). Controls In addition to the power ONlOFF switch (an adjacent LED indicates power-on in ac operation), the front panel contains five individual input gain controls designated MIC 1 through MIC 4 and AUX, and a MASTER gain con- trol for the total program output. Note that the input connectors are located on the rear panel directly behind their corresponding gain controls. The M268 has feedback-type active gain controls for lower noise and greater dynamic range. In general, the individual gain control adjusted for the required output. If overload distortion (clipping) occurs when using high- level sources, reduce the individual gain control set- tings. Unused individual gain controls should be kept at the minimum setting (counterclockwise). Mix Bus The rear-panel MIX BUS phono jack facilitates the "stacking" of mixers to obtain additional inputs without using any of the M268 inputs. Connecting the mix buses of two M268s, for instance, directly connects their mix- ing systems, providing two independent master con- trols and two isolated output amplifiers with 10 in- dividually controlled inputs. Note that the gain will be reduced by 6 dB, but noise specifications are not ' Designed to mate with Cannon XL series, Switchcraft A3 (Q.G.) series or equivalent connector. Simplex Power The M268 provides power for condenser microphones such as the Shure SM81 and SM85. The rear-panel SIMPLEX OFFION switch controls the application of simplex voltage to all low-impedance inputs. With the SIMPLEX switch on and the rear-panel LOlHl switches in the LO position, + 30 Vdc is applied to pins 2 and 3 of each input connector. Series current-limiting resistance is 3.3 kilohms for each input. When using other con- denser microphones with the M268, verify that the voltage and resistance requirements are compatible. Balanced low-impedance microphones (dynamic, rib- bon, self-powered condensers) can be used in combina- tion with simplex-powered condenser microphones. IM- PORTANT: Do not turn on the SIMPLEX switch when using unbalanced low-impedance microphones; objec- tionable hum will result. Turn off the SIMPLEX switch when condenser microphones are not being used. Use only high-quality cable, as intermittent shorts between broken shield wires and balanced conductors will cause offensive noise transients in the system. BATTERY OPERATION - EXTERNAL POWER In addition to ac operation, the M268 can be operated from an external battery supply (Shure Model A268B) or any well-filtered dc supply providing 30 Vdc. Current drain is typically 12.5 mA at 8.OV output level. Battery operation is recommended both for remote, on-location operation, and as an emergency source in case of failure of the ac power source. The A268B contains three 9-volt transistor radio bat- teries which will power the M268 at full rated output. Alkaline battery life is approximately 40 hours at 4.OV output, 4 hours per day use. Note that battery operation with simplex-powered microphones will increase bat- tery drain. To power the M268 from an external 30 Vdc source, obtain a power plug (Switchcraft S-760 or S-765 or equivalent) and attach it to the power source leads, observing proper polarity. CAUTION: The 30 Vdc input circuit of the M268 is not fused. An external 30 Vdc source should be provided with a 0.25A, 250V in-line fuse as a safety precaution. With a battery supply or external dc supply con- nected, the M268 will automatically and silently switch to battery operation should the ac line voltage fail. ACCESSORIES The Model A268B Battery Power Supply can be used as a sole source of power for the M268, or as a standby supply in case of ac power failure Attaches to side of M268. The Model A268R Rack Panel Kit consists of a 19 in. x 3% in. (483 mm x 89 mm) precut rack panel and necessary hardware for rack mounting the M268 in a standard 19 in. (483 mm) rack panel.