What is the dB output range of the ULXP4 receiver output level potentiometer knob? (does it add, + gain above 0 dB at full gain, or does it output 0 dB at full gain?)1) The ULXP4 does not a provide a true line level output, i.e, nominal +4dBm.
2) The Mic/Line switch on the rear panel provides a boost of 30 dB over the MIC position.
3) Per the ULXP4 User Guide, the maximum output level with a LINE setting is 3.9 dBV. Therefore, the typical/nominal output level is 20 dB below that, or -16 dBV.
4) The receiver output level control is an attenuator only. It should be set to maximum, and lowered ONLY if the ULXP4 is clipping the input of the following device.