The NM 1 Network Mic Preamp is a very versatile single channel CobraNet I/O box that finds use in many applications. The NM 1 presents matchless features in a compact, reliable, easy to install and maintain package. It has a single studio-grade microphone input with +48 volt phantom power, and a single amplifier output for connection to an external loudspeaker. The microphone signal can be transmitted over CobraNet and the amplifier input can be driven by any CobraNet audio channel. The NM 1 design is based on the Cirrus Logic CS18101 CobraNet chip and CM-2 reference design including the secondary CobraNet port for data and power supply redundancy (more on this later). It also has logic I/O on a DB-15 connector for reading external switches and driving indicator LEDs so it can be connected to a custom switch panel to implement microphone enable, busy indication and similar functions.
The feature that adds the most versatility to the NM 1 is Power Over Ethernet (PoE). It is fully compliant with the IEEE 802.3af standard as a Powered Device (PD). This means it’s powered through the CAT 5 cable that connects it to an Ethernet switch. Of course, the Ethernet switch used must comply with the 802.3af standard as Power Supply Equipment (PSE); these switches are available from all the major Ethernet equipment manufacturers.
Think about this: the NM 1 does not need a power outlet close by. No AC line voltage wiring. No additional electrical box in the wall. No wall wart, batteries, solar panel, pedals or water wheel. The only wiring needed is the data cable back to the Ethernet switch and the local analog audio, making planning and installation much easier and much less expensive.
Rane’s engineers have designed the NM 1 to have a redundant PoE supply along with the redundant data connections. It can be powered from either Ethernet port independent of which one carries the CobraNet data, so an independently redundant power system comes along with the redundant data system with no redundant effort. Switching between ports for PoE is almost seamless and audio interruption is minimal. If the primary port fails the secondary port takes over very quickly, typically 10 ms, without loss of programmed settings.
All parameters are controllable via standard SNMP messages including microphone gain and muting, amplifier output level and muting, and CobraNet Audio channel and Bundle assignments. Four exterior switches assign the NM 1 MIB’s SysName variable to uniquely identify each unit on the network.
All NM 1 audio and data connectors are metal with locking, annular-ring shields for maximum durability, security and immunity from electromagnetic interference, be it radio, static or legislative hot airwaves. And all this fits in a very rugged (but good looking) extruded aluminum box.
The NM 1 hardware ships with Rane’s NM 1 Search and Control software for Windows XP. The Search software polls a network for all connected CobraNet devices and displays their System Name (sysName), IP Address and MAC address. While Polling you can assign them different IP Addresses if needed. Exiting Polling mode reduces the list of CobraNet devices to only the NM 1s. NM 1 Search is much like Peak Audio’s Disco application, without the Bee Gees music built in. Disco doesn’t give you much insight into what the NM 1’s capabilities and settings are unless you study the NM 1 MIB & DB-15 logic in detail by reading the manual. We know you avoid reading manuals since your spouse may catch you. Disco’s advantage is its ability to view many more MIB variables than the Rane software. So using both is typical, especially if you’re new to the NM 1.
Once you stop the Search software’s Polling, double-clicking on a found NM 1 opens the Control section of the software where you can set each NM 1’s common parameters and monitor the state of their logic input (switch) and (LED) output states. Note that multiple instances of the Control software is supported. The NM 1 parameters adjustable from the Control dialog are: mic gain, transmit Bundle, receive Bundle, Conductor Priority, plus the mic mute (via Talk), private mode, override enable, cough enable and Persistence. The read-only NM 1 parameters are also displayed for you in full living color: talk, private, cough, and override LEDs. See the primer on logic, below.
When you install the NM 1 software, it copies the NM 1 data sheet, manual, and the NM 1 MIB and CobraNet MIB to your hard drive. Get all the other gory details in the software’s Help file. Note the Persist variable setting discussed in the help file, particularly if you’re in a rush (and who isn’t). We warned you, in writing.
NM 1 IP ADDRESS & CONTROL
The IP address in the NM 1 is lost when power is disconnected, it is not persistent. This means it would behoove you to carefully write your SNMP control software. Most systems use either the NM 1’s sysName variable or the MAC address to uniquely identify each NM 1, then send it an IP address for control. Some people use the network switch’s ability to identify which source address packets are coming from which port/device to allocate IP addresses. Using the sysName has an advantage when it comes to maintenance since, were an NM 1 need replacing (or if you reconfigure the room or add or subtract NM 1s), simply setting the hardware sysName switches correctly on the replacement NM 1 makes identification more convenient than using MAC address or switch port. While CobraNet does not use the IP address for audio packet delivery (it uses MAC addresses), SNMP requires IP addresses.
NM 1 BUNDLES & OTHER FUN
The NM 1 transmits a single audio channel within a single Bundle. It also receives a single audio channel in a single Bundle. By default, the NM 1 uses Audio Channel 1 within the transmitted and received Bundles. While Bundles typically contain up to 8 Audio Channels, by default, the NM 1 transmits only a single Audio Channel in its Bundle. This is achieved by setting the NM 1’s CobraNet TxSubCount variable to 1 (not 8). This means that only a single Audio Channel is transmitted which significantly reduces the data being transmitted on the network. Of course, any of the NM 1 settings can be changed using standard SNMP set and get messages.
PRIMER ON NM 1 DB-15 I/O LOGIC
The Talk input is permanently set up to be a momentary toggling function. Use a momentary switch, of course. Hit is once, it mutes, hit it again, it unmutes. Lather, rinse, repeat. The corresponding Talk output permanently follows this functionality.
The Private input functions the same way Talk does, as a permanent momentary toggle. The Private output follows this functionality, always.
The Override input is a push-to-talk. Hit it and the mic is on. It also overrides the Mute, so if the Mute is on, Override unmutes it while the Override input is grounded. However, the Override input can be ignored by setting the overrideDisable MIB value. In other words, set the overrideDisable to 1 to cause the override switch to have no effect on the Talk function. [Setting overrideDisable true (1) means override is disabled.] Asserting overrideDisable does not change the function of the Override LED (output). This means you can completely customize the Override input function and disconnect override from the audio. For example, use the Override input for voting Yes and the override LED to indicate a Yes vote. Or implement a page switch instead.
The Cough input functions exactly like the Override input & output, except the Cough is a push-to-mute — or what we affectionately call push-to-cough.
On the rear panel are four rotary switches used to create a four digit identifier that becomes part of the SNMP variable, sysName.
sysName is then used to uniquely identify a CobraNet device on the network. The condition of being unique requires that each device on the network have a different setting. Looking at the unit with the switches facing you, the identifier reads from left to right.
Thus, setting the switches to 1, A, 3, 7, respectively, sets the sysname variable to “NM1-Sw1A37.”
COBRANET PRIMARY Connector
COBRANET SECONDARY Connector
These Neutrik Ethercon connectors accept CAT 5e Ethernet cables terminated with the standard RJ-45 plug. They are used as the Primary and Secondary connections to a LAN carrying CobraNet data. The Ethercon connectors also accept a Neutrik-designed housing for RJ-45 plugs (Neutrik NE8MC series) that is similar to the industry standard XLR connector. This Ethercon plug is much more rugged than the standard RJ-45; a version of the housing is available to retrofit over CAT 5e cables that are already terminated. (Note that certain cables such as Belden MediaTwist require special strain-reliefs to work with the Ethercon shell.)
The cabling used to connect the NM 1 to other Ethernet equipment must be CAT 5e minimum. CAT 6 is also acceptable. For more information about CobraNet network design, redundancy, and Primary and Secondary ports, please refer to CobraNet documentation from www.cobranet.info.
Both the Primary and the Secondary ports fully support PoE (IEEE 802.3af). For the NM 1 to operate, at least one of the two Ethernet ports must be connected to a device that is an IEEE 802.3af compliant Power Source Equipment (PSE). Power can be supplied to the NM 1 through either the unused pairs of the CAT 5 cable, or in a “phantom power” scheme using the data pairs. This allows the use of PSE devices from manufacturers that support either scheme. The NM 1 requests the maximum power, approximately 13W, on both ports (see data sheet for details on power requirements). The PSE must be chosen carefully to ensure that it can provide full power to every port that is connected to a NM 1.
Power can be supplied to the NM 1 through either port; it automatically switches between the ports to support fully redundant system designs. If power is available on both ports, the NM 1 chooses one as the active power port. PoE supports equipment hot-plugging, so a PSE senses when a load is disconnected and stops delivering power on that port. To allow the fastest possible switch-over from the active port, the stand-by port always draws a minimum current from its PSE so the PSE is awake and ready to deliver power as soon as the NM 1 needs it. This allows seamless redundancy in the power supply to the NM 1. Note the port the NM 1 chooses to power from is independent from the port that is being used for CobraNet data.
In Use / Conductor LEDs
There is one yellow LED for each CobraNet port. This indicator lights on the port in use and blinks if the device is also the Conductor.
Link / Activity LEDs
There is one green LED for each CobraNet port. This indicator lights when Link is established and blinks when CobraNet network activity is detected. (More documentation at www.cobranet.info)
SWITCHES / LIGHTS Connector
This female DB-15 connector allows an external switch and lamp panel to be attached for push-to-talk, cough mute, and other similar functions. It is provided with lugs so that any DB-15 plug with mounting ears and spring-latches can be used (e.g. Amp part numbers for the spring latch are 745779-3 (bulk), 745779-2 (two/bag), 745255-3 (bulk) or 745255-2 (two/bag) )
Switches / Lights Connector Pinout
Pin 1 Talk button
Pin 2 Cough button
Pin 3 NC
Pin 4 Override button
Pin 5 Private button
Pin 6 Ground
Pin 7 Ground
Pin 8 Ground
Pin 9 Ground
Pin 10 Ground
Pin 11 Talk LED
Pin 12 Cough LED
Pin 13 NC
Pin 14 Override LED
Pin 15 Private LED
The LED output pins provide +12 VDC through 160Ω current limiting resistors when they are turned on. When turned off, they are floating. LED indicators should be connected between these pins and ground pins on this connector. The switch inputs have internal pull-ups to +3.3 VDC and are ESD protected. When a pushbutton input is needed, normally-open switches should be connected between one of these inputs and a ground pin.
This amplifier output is a standard 1/4" TRS phone connector. It is used to connect a 4Ω minimum loudspeaker to the NM 1 for monitoring the selected CobraNet audio channel. The NM 1 power amplifier can deliver 1 watt continuously into an 8Ω load with a pink noise signal that has a 15 dB crest factor (see data sheet for detailed specifications). The output configuration requires that the positive and negative signals must remain isolated from the chassis and from ground. The plug used must be TRS; use of a TS (i.e. mono) phone plug shorts the power amplifier and causes a malfunction. The threaded metal bushing allows use of a 1/4" phone plug with a threaded locking ring (e.g., Switchcraft Number 298). The connector sleeve is connected directly to chassis ground; the tip is the positive signal; the ring is the negative signal.
MIC INPUT Connector
The balanced microphone input is an industry standard XLR-3 type connector (see Data Sheet for specifications). Gain is adjusted via SNMP control. IEC 61938 P48 compliant 48V phantom power is provided. Connect pins 2 and 3 to the balanced output of the microphone. Pin 1 is directly connected to the chassis; for best noise immunity, the microphone cable should have a braid or double wound shield. If a cable such as Belden 1800F is used that has both a wire shield and a drain wire, then all the shield wires and not just the drain wire should be connected to pin 1 of the XLR connector.