System Interface Interfacing any recently manufactured piece of audio equipment into your studio can be challenging, perhaps even painful. It doesn�t have to be. Still, with the wide variety of different input and output circuit topologies, it doesn�t hurt to have a bit of background information. Input The AD9624 has two balanced inputs, appearing on XLR connectors. Pin 1 is ground, and it connects directly to the chassis as well as to the internal circuit ground. Pin 2 is hot, and pin 3 is cold. A simple differential amplifier implements the balanced input. Coming from a balanced system, it should be as simple as plug and play. Leave pin 1 connected unless you hear hum. You can try lifting it (at the source). Use whichever method results in the lowest noise floor. Ideally, you should only hear hiss. Coming from an unbalanced system, the best connection method takes advantage of the AD9624�s balanced input (in spite of the unbalanced source). Do this by running shielded twisted pair (that�s 2 wires plus the shield; i.e. balanced mike cable) from the AD9624�s balanced input to the output of the unbalanced device. Once there, connect the hot lead to the unbalanced source�s hot lead, connect the low lead and the shield together and connect them to the ground of the unbalanced device. Note If you want the absolute lowest noise floor, then you really should operate the AD9624 in a fully balanced environment. Output The DA9624 has two balanced outputs that appear both on XLR connectors as well as 1/4-inch TRS connectors. The connectors are wired in parallel, so doing something electrically to one affects the other. Two cascaded inverting amplifiers implement the balanced output. This simulates a transformer winding with its center tap connected to ground. In a balanced system, simply plug and play. Again, pin 1 is ground, pin 2 hot, and pin 3 cold. You may need to float pin 1, preferably at the DA9624. In an unbalanced system, things get a bit more complicated. There are three options. 1. Float (do not connect) the cold side of the output. For the XLR connector, this is pin 3, for the TRS connector it is the ring. Note that there is a -6dB level difference for this connection. 2. Insert a tip-sleeve phone plug into the TRS connector and go for it. The bad part of this method is that one side of the balanced output gets to drive a dead short. The worst of it is that the short circuit current (which is not musical in the least) flows into the ground system,where it could cause trouble. Please: try to do this only when forced to.
