NM-250 MKII: A Newsroom Headliner

It used to be that the demands put on a newsroom mixer and full broadcast console were far different. Today, news staffs are called on to mix and match material from many sources, requiring more sophisticated capabilities.
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It used to be that the demands put on a newsroom mixer and full broadcast console were far different. Today, news staffs are called on to mix and match material from many sources, requiring more sophisticated capabilities.

Over the past few years, Dixon System’s NM-250 has gained a following by providing a mixer that meets this need, aiming to combine the simplicity and ease of operation typically associated with a newsroom mixer with a broadcast console’s power and flexibility. The company says it has about 1,000 units installed. The NM-250 MKII refines and improves the company’s concept.

For those familiar with the original NM-250, this upgrade includes numerous improvements suggested by feedback from the field. These include quieter inputs that can be set to line or mic levels with jumpers, and phantom power. Integrating a telehybrid is now simple with the new mix-minus bus alongside an input for the return from it.

The package meets most needs for a news operation in a convenient 2 RU unit.

Easy to figure


(click thumbnail)The beauty of the NM-250 MKII remains the simplicity of its controls. A bottom row of pots controls levels. Starting on the left, a pair is marked for microphones, then single pots are labeled for phone, computer and line one and two. There is a 1/8-inch front input jack with a dedicated pot for adding a field recorder. Each has a pushbutton cue switch. A second strip of on/off switches with LED light over them either engages or disengages these.

On the right, a two-channel LED for levels is over pots for the monitor and headphone. Two talkback switches include LEDs to identify who’s calling. A switch under a headphone jack toggles between off-air and mixer. For the typical applications, even non-technical talent can grasp the self-explanatory layout.

The rear panel connectors are fairly straightforward. The bottom wiring row is labeled for program outputs, monitor, mix/minus off-air in, talkback in and talkback send 1 and 2. An added feature is that these connectors interface with a pop-out component. Wires are screwed down into the pop-out, then attached to the back.

This arrangement makes for more flexible installation and maintenance than if wires were attached directly. Instead of having to pull the whole unit from the rack to check connection, you pull the pop-out. Above this, a row of female XLR connectors are set up for the line ins, phone and mics. A pair of unbalanced RCA connectors serves as the I/O for a computer soundcard.

A cleaner sound

The major component upgrade for the MKII is the three new low-Z mic preamps. The first two are used for the mics; the last is intended for configuration as the line input return for a telehybrid.


(click thumbnail)Detail of the rear connectors. The bottom wiring row is labeled for program outputs, monitor, mix/minus off-air in, talkback in and talkback send 1 and 2. The connectors interface with a pop-out component.The original components were sufficient for most radio applications, with S/N ratios of around 65 dB. Considering that the signal quality is only as good as the weakest link, this is a pretty decent spec especially for AM radio applications. But with the coming digital radio advances as well as additional applications for the NM-250 as a remote mixer, the new high-grade components bring the S/N ratio much lower. The published specs of under 80 dB are borne out with tests of the demo unit showing 85 dB.

Beyond the mic preamps, the unit is quiet from the use of 1 percent metal-film resistors all through the audio path and the power supply’s toroidal transformer. While a lot of newsroom work is of the “quick ‘n dirty” variety where time is of the essence in breaking stories, it’s nice to know that the MKII doesn’t contribute to any of the rough edges that go with the territory.

Other adds for the MKII include start and stop pulses for the telephone and computer inputs. A 100 ms pulse to ground can be used to operate computer playback as well as telehybrid operation.

Overall, the NM-250 MKII is a well thought out, an easy choice for a busy news operation. The front jack 1/8-inch input is especially welcome for field reporters wanting to get sound they’ve gathered out to the audience without any hassle. For larger operations, maintaining consistency from workstation to workstation makes it simple for staff to work at different locations with the same interface. Also, the rackmount design opens valuable desk space.

Downsides are the unbalanced RCAs for the computer interface and the thin gauge metals used for the cover/case. The computer I/O is designed to save the need for a balanced/unbalanced adapter typically used to bring consumer-grade components — here, a generic computer’s soundcard — into the professional broadcast mix.

Even though the quality of consumer soundcards has come up considerably, the real issue is that using any unbalanced audio connector near a PC is an invitation to trouble. PCs typically generate a variety of electrical noise from the computer’s power supply and motherboard and the best way to sidestep it is by using a professional audiocard with a balanced I/O. But with the MKII, you’ll need to use a balanced/unbalanced adapter to attach a professional soundcard. Far better to scrap the RCAs for balanced TRS jacks in the first place.

The question of the case for the unit is perhaps a bit picky. The NM-250 MKII is not designed to be a portable mixer and the components inside the box will be perfectly safe when properly installed in a rack. Still, the aluminum top of the case seems a bit thin and flexes in without too much weight or pressure applied. Tossing it on top of the pile at a workstation is not a good idea.

The NM-250 MKII is a workhorse for the contemporary radio newsroom and a significant improvement over adapting general-purpose mixers for this highly specific broadcast task.

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