Input and Output Audio Connections

The SEND IN input connection has the following characteristics:

• XLR Pin 1 = Ground

• XLR Pin 2 = High (Active balanced, RF suppressed)

• XLR Pin 3 = Low (Active balanced, RF suppressed)

• Bridging impedance > 100K Ohm

• Analog clip point = +24 dBu

• Analog-to-Digital converter resolution = 24 bits

• Adjustable input level from -10 to +8 dBu

• Switchable LINE and MIC level input range

The unit can accommodate a line input level between -10 dBu and +8 dBu, adjustable with a trim pot on the rear panel. The input level is set to +4 dBu level from the factory.  A +4dBu signal fed into the SEND IN connector should light the Yellow LED bar graph segment on the Front Panel. If more input gain is needed, turn the trim pot CLOCKWISE to increase the gain and match the operating level of the hybrid.

Note - Increasing the send level beyond a normal meter reading does not increase the level into the telco line due to the hybrid’s AGC and limiting. You will only add distortion and degrade the hybrid’s performance. There is a dip switch configuration option that applies an extra 3dB gain after the AGC should you need more send level. See the section on Rear Panel DIP Switches for details.

Next to the input level pot is a pushbutton switch that selects between line and mic levels. When the pushbutton switch is in the LINE position (out), the input range of the SEND IN signal is –10 to +8 dBu. When the switch is in the MIC position (in), the input range of the SEND IN signal is –70 to –52 dBu.

The inputs are designed to be sourced from balanced lines. Usually, shielded cables have the shield wire connected only on one end (most often at the input) to prevent ground loops. Older equipment with a transformer output stage may need a terminating resistor across Pins 2 and 3 to maintain a proper “flat” frequency response. Consult the manual for your equipment for how to use it with high impedance inputs.

If you are connecting a device with an unbalanced output to your Hx, connect the shield from the output of your device to Pin 1 (ground) on the Hx input, and the “hot” lead from your unbalanced output to Pin 2 (high) on the Hx.

Depending on the device, you might also want to try connecting Pin 3 of the Hx input to ground or “floating” the ground and using only the high and low pins on the Hx.

It’s also important that unbalanced lines be kept short to avoid hum and noise pickup. You’ll probably need to adjust the input gain on the Hx to match the output of your device.

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 information and suggested wiring and grounding techniques for your studio or recording workstation, please visit the Telos Alliance support page.

Output Audio Connections

The output connection, RCV OUT, has the following characteristics:

• XLR Pin 1 = Ground

• XLR Pin 2 = High (Active balanced, RF suppressed)

• XLR Pin 3 = Low (Active balanced, RF suppressed)

• Output impedance < 60 Ohms

• Analog clip point = +24 dBu

• Digital-to-Analog converter resolution = 24 bits

The nominal output level is fixed 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 information on suggested wiring and grounding techniques for your studio or recording workstation, please visit the Telos Alliance support page.