12 | Section 2
e nominal output level is xed at +4 dBu, with +20 dBu headroom to account for the crest
factor of some audio signals.
If you are connecting the output of your Hx to a device with an unbalanced input, connect the
shield from your device’s unbalanced input to pin 1 (ground) on the Hx, and the “hot” lead from
your device to pin 2. It’s important that unbalanced lines be kept short to avoid hum and noise
pickup. We also suggest that all of your audio equipment be powered from the same AC power
source or circuit to prevent ground loops due to the use of multiple grounds. For complete infor-
mation on suggested wiring and grounding techniques for your studio or recording workstation,
please visit the support page at the Telos website: http://www.telos-systems.com/support.
2.6 Remote Control
e female DB9 connector on the Back Panel provides access to control functions. Pin 1 of the
DB9 connector is Ground. Pins 2 through 5 on the top row are for GPIO input signals from
the remote device, while Pins 6 through 9 on the bottom row are GPIO output signals to the
remote device. Two of the GPIO input pins and two of the GPIO output pins are reserved for
each hybrid as follows:
Input Characteristics
♦ e GPIO inputs are designed to be universal. ey accept either a voltage source up
to 24VDC, or a closure to ground, which may be provided by switches, relays, or logic
outputs. In the latter case either ‘totem-pole’ or open-collector will work. e inputs are
active low.
♦ A built-in 1k Ohm pull up resistor is provided.
Output Characteristics
♦ Open-collector to ground.
♦ ese will require a pull-up resistor to drive TTL-style logic inputs. Most equipment has
the pull-up built into the input, but if there is no pull-up, you’ll have to add one, connect-
Pin No. Function
1 GPIO Ground
2 GPIO IN Hybrid #1 - Hybrid ON
3 GPIO IN Hybrid #1 - Hybrid OFF
4 GPIO IN Hybrid #2 - Hybrid ON
5 GPIO IN Hybrid #2 - Hybrid OFF
6 GPIO OUT Hybrid #1 - ringing indicator
7 GPIO OUT Hybrid #1 - ON/OFF status indicator
8 GPIO OUT Hybrid #2 - ringing indicator
9 GPIO OUT Hybrid #2 - ON/OFF status indicator
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