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Dixon Systems NM-250 MKII Owner's Manual
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Dixon Systems NM-250 MKII Owner's Manual

Newsroom mixer
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Dixon Systems
Model NM-250 MKII
Owner's Manual

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Summary of Contents for Dixon Systems NM-250 MKII

  • Page 1 Dixon Systems Model NM-250 MKII Owner's Manual...
  • Page 2 The NM-250 MKII newsroom mixer is designed for newsroom work-stations and contains almost all the features of a full stereo broadcast console in a two rack-space unit. The NM-250 MKII retains all the features of the original NM-250 but adds a number of features and improvements.
  • Page 3 DAMAGE CLAIMS MUST BE MADE BY THE CONSIGNEE. Environmental Considerations The NM-250 MKII will operate satisfactorily over a wide range of ambient temperatures. If installed in an area with high heat producing equipment, adequate ventilation is necessary to prolong the life of components.
  • Page 4 Dixon Systems NM-250 MKII Performance Specification Line Inputs Balanced Inputs Source impedance 600 Ohms Input impedance 40 kOhms Input level Nominal +4dBm Maximum input level +28 dBm Unbalanced Inputs Source impedance < 2 kOhm Input impedance 20 kOhms Input level Nominal -10 dBu Distortion &...
  • Page 5 Dixon Systems NM-250 MKII NM-250 MKII Simplified Block Diagram...
  • Page 6 NM-250 MKII Microphone Inputs The NM-250 MKII has three low-Z microphone inputs. They are identical, except that Mic 1 is also used as part of the Talkback send system and the third input is normally configured as a line input return from the telephone hybrid. Input connectors are XLR type and are located on the rear panel.
  • Page 7 Talkback # 1 has been designed to permit the use of a TCC or single pair for both send and receive. This is most often used when the NM-250 MKII is acting as a remote mixer. New in the ‘250 MKII are tally lights that indicate who is calling.
  • Page 8 As indicated earlier, talkback # 1 can be used with a single twisted pair, (sometimes referred to as a TCC) most often when the NM-250 MKII is used as a remote mixer.
  • Page 9 These provide a pulse to ground of approximately 100ms. Some customers are using the NM-250 MKII as a remote mixer. If desired, and a phone channel is not required, this input can also be and used as a third microphone input.
  • Page 10 This is not necessary with the NM-250 MKII. There are four RCA-type connectors on the rear panel of the unit, two as inputs coming from the sound card and two which send audio to the sound card.
  • Page 11 NM-250 MKII Front Panel Input Jack Another useful feature of the NM-250 MKII is its front panel input jack. This is a miniature tip/ring/sleeve jack, common to many cassette and DAT machines. It allows the user to quickly dub an interview, etc. to the computer’s hard drive so that it can be edited in the computer.

  • Page 12: Line Level Inputs

    Dixon Systems NM-250 MKII Line Level Inputs There are two active balanced +4 dBm line level inputs to the NM-250 MKII. Both are identical. Connections are made via XLR type connectors located on the rear panel of the mixer. These inputs would normally be connected to the output of a simple switch bank, or in more elaborate installations, a routing switcher.
  • Page 13 Dixon Systems NM-250 MKII Master Output Amplifiers Again, a 5532 is employed as a summing amplifier, this time with one half of the op- amp connected to the left program bus, the other half connected to the right bus. The outputs of the summing amplifiers are connected to the master output gain control trim- pots located on the main PC board.
  • Page 14 NM-250 MKII Summing Amplifiers All summing amplifiers in the NM-250 MKII are standard current summing devices. As seen in the schematic below, signals from the cue summing bus are applied to one half of a 5532 op-amp. Signals from the mix-minus bus are applied to the other half of this device.

  • Page 15: Monitor System

    NM-250 MKII Monitor System The monitor system in the NM-250 MKII makes this mixer extremely versatile. It contains a built in headphone amplifier, a line driver for the RM-35 (or other) stereo monitor amplifier, a cue system, talkback returns, and an external input for an off-air feed.
  • Page 16 NM-250 MKII Metering The NM-250 MKII uses the LM3916N-1 monolithic integrated circuit to provide an electronic version of the VU meter. The metering circuitry is on both the main PC board and the PC board which mounts behind the front panel.

  • Page 17: Monitor Outputs

    N.B. If the mute relay is used to control a studio ‘on-air’ light, do not attempt to use 110 VAC with these contacts. We recommend the use of a solid state zero cross relay with the NM-250 MKII controlling a low DC voltage to operate the solid state relay.

  • Page 18: Power Supply

    Dixon Systems NM-250 MKII Power Supply The NM-250 MKII requires an electrical mains supply of 110 V AC 60 Hz, preferably from isolated sources. A three-wire AC cord is used with the third wire connected to the chassis and ground.
  • Page 19 NM-250 MKII Logic and Control All signal switching in the NM-250 MKII is accomplished using miniature 24 VDC relays. Each time a microphone is turned on, it activates the Mic relay (which delivers audio to the summing bus), illuminates the ‘channel on’ LED, and, if the mute jumper is installed, activates the mute relay.
  • Page 20 Dixon Systems NM-250 MKII Circuit Locations Talkback send Talkback receive Off-air input Mix-minus send Monitor output stage Main PC Board Master output stage Master summing amp Monitor summing amp Power supply 10) Headphone amp 11) Cue/Mix-minus summing amp 12) Mic. 1 input 13) Mic.
  • Page 21 Dixon Systems NM-250 MKII Rear Panel Connections All input and output connections are made at the rear of the unit with the exception of the front panel input, designed for cassette or DAT input, and the headphone jack. The rear panel is silk-screened and inputs/outputs are identified.
  • Page 22 Dixon Systems NM-250 MKII Notes:...
  • Page 23 Dixon Systems 580 Danforth Road Toronto, Ontario, Canada M1K 1E3 www.dixonsystems.com e-mail: helpdesk@dixonsystems.com...