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ULN-2 Users Guide
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1x is generally appropriate for use with devices that provide a word clock output. If your device provides
a 256x output, you may find that you get better results using that clock signal. The Digidesign® line of Pro
Tools® products use 256x as their “ SuperClock™” clocking signal.
The AES recommended procedure for distributing clock is to use an AES clock signal. The AES clock signal
is an AES digital audio signal with no audio activity. ULN-2 only uses the AES preambles for clock recovery,
so it is immune to data dependent jitter effects. This means you can reliably use the Digital Input as a clock
source with or without audio data.
FireWire
Detailed information on FireWire implementation can be found in the FireWire appendix.
Power
One of ULN-2’s many great strengths is the flexibility of its power system. ULN-2 can be powered from any
DC source (including bus power) in the range of 9V to 30V as long as it provides 12 Watts of power. The
DC inputs on ULN-2 are a 2.1mm coaxial power connector, center positive and a 4-pin XLR connector Pin
4 Hot. So if you are powering the unit with a third party power source and it supplies 9V, the power source
will have to provide 1.4 amps of current. If you are powering the unit with 12V, the power source will have
to provide 1 amp of current, and so on.
The ULN-2 ships with a world-ready 24 volt, 2 amp power supply. You can plug this supply into any AC
power source from 90V to 240V, 50Hz - 60Hz, using an appropriate IEC power cord, and it will supply the
proper power to the ULN-2 on the 2.1mm coaxial power connector. ULN-2 will automatically supply the extra
power to the FireWire bus. This means that the ULN-2 and its power supply can be used to power other bus-
powerable FireWire devices including hard-drives, hubs, and other ULN-2 units.
Since ULN-2 is DC powered, you can also power up the ULN-2 using the FireWire bus or another DC source.
The ULN-2 uses 12 Watts of power, so the device supplying the bus power must be capable of sourcing
that much power. Most desktop Macs provide more than enough power for ULN-2 and one other low power
device. Most laptops provide enough power for ULN-2, but not enough for ULN-2 and another bus-powered
device at the same time. If you are using a Powerbook computer, you should not expect to be able to power
both the ULN-2 and a hard drive from the computer. The power capabilities of individual computers vary, so
you will have to test the complete system to determine exactly how much your computer can handle.
If you find that the computer is not capable of powering ULN-2 or does not provide enough run time, you
may want to explore using an external power source with the ULN-2. Check with Metric Halo for details on
different battery power solutions for ULN-2.
As with all electronic devices, when connecting an external power source to the ULN-2, you should first
connect the power source to ULN-2 while it is in an unenergized state (e.g. not connected to the mains or
switched off). After the connection to ULN-2 has been made, you should energize the power source.
If you connect an energized power source to the ULN-2’s 2.1mm power connector you may see a small spark
when you make the connection. This is due to surge current and is normal if you connect a power source
in this way. While this will not damage the ULN-2 in any way, to avoid the spark just connect the power
connector to ULN-2 before connecting the power source to the wall.
ULN-2 Specifications
Table 6.1. Mic Inputs
Mic Inputs
Stepped Gain Range +6 dB – +72 dB (6 dB Steps)
Gain Range with Trim -14dB – +70 dB
Input Impedance 3.3k Ω