ULN-2 Users Guide
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1 and 2. Each optical channel continues to transmit data at 1x speeds, and both devices are required to
multiplex and demultiplex the audio into and out of the optical channel pairs.
Clock Sync
Clock sync is a serious consideration in any digital audio system. The ULN-2 and any of it's digital audio
interfaces can be used as the master clock source either for the ULN-2 by itself or for a full daisy-chained
MHLink domain. In this regard, all 3d-equipped Metric Halo boxes are equal - only the physical I/O com-
plement differentiates the box models.
If you are recording analog sources with ULN-2 by itself or as the root box of an MHLink domain, you can
simply use the next-generation 3d internal clock source to drive the converters. This is the easiest case
to deal with.
If you need to interface with other devices digitally or ensure sample accurate sync with video sources,
the extensive clock synchronization capabilities of the 3d ULN-2 will prove to be more reliable (and better
sounding) than much higher priced alternatives.
There are four different ways to get external clock information into the unit:
1. Sending a word clock signal into the WC Input BNC.
2. Sending an AES signal into the XLR Digital input.
3. Sending an S/PDIF signal into the RCA Digital input.
4. Sending an ADAT or S/PDIF signal into the Optical Digital input.
The BNC word clock input port is a 75 Ohm terminated coaxial input. It should be driven by a 75 Ohm
source driver and interconnected with 75 Ohm coaxial cable. Even though the clock recovery qualities of
the 3d hardware are second-to-none, incorrect cable impedance will introduce reflections on the word
clock cable (jitter) which may adversely affect clock stability and audio quality.
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. The ULN-2 only uses the AES preambles for clock
recovery, so it is immune to data dependent jitter effects. This rule applies to both the XLR AES and RCA
digital inputs, which means you can reliably use the Digital Inputs as a clock sources with or without audio
data.
The Optical input port will automatically adjust to any ADAT or TOSLINK signal it recieves at whatever
sample rate. For example, incoming ADAT data SMUXed at 96kHz will be decoded automatically as 4
channels of audio clocked at 96kHz requiring no adjustments from the user. That said, ADAT/TOSLINK
optical connections are generally more susceptible to jitter artifacts than copper AES, S/PDIF or word clock
sources.
Power
One of the ULN-2’s great strengths is the flexibility of its power system. The ULN-2 can be powered from
any DC source in the range of 9V to 30V as long as it provides 12 Watts of power. The ULN-2 provides two
power supply inputs: a 2.1mm coaxial power connector (center positive), and a broadcast battery-com-
patible 4-pin XLR male (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 18 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 3d on the 4-pin XLR power socket.
Unfortunately, the power capacity supplied through a USB bus is unsufficient to power a Mobile I/O.
