The ground terminal of the IEC plug is required by wiring codes and regulations. It must always be
connected to the electrical installation safety ground. The LSR units have carefully designed internal ground-
ing and balanced inputs and outputs to reduce the event of ground loops (hum). If hum occurs, see Appendix
A for suggested correct audio signal wiring and system grounding.
4.3 Audio Level Adjustment:
The audio level sensitivity of the LSR28P can be adjusted for almost any situation. Monitor outputs
on consoles are normally at a nominal level of +4 dBu or -10 dBv. These are typically called professional and
The LSR28P can be set up for fixed or variable gain. As shipped from the factory, the nominal input
level of the XLR input is +4 dBu and -10 dBv for the 1/4" T/R/S input. A nominal level to these inputs will
produce an output of 96 dB SPL at 1 meter in an anechoic environment. This allows the user to get a good
match when using either professional or semiprofessional equipment. If less sensitivity is needed, 4, 8 or 12 dB
of signal attenuation can be inserted using the DIP switches on the back.
Switch 1 enables the input trim pot. With the switch in the down position, the trim pot is out of the
circuit and does not affect the input sensitivity. In the up position, the input trim is added to the circuit and
will attenuate the input level from 0 - 12 dB from nominal.
Switch 2 inserts 4 dB of attenuation to both the XLR and 1/4" T/R/S inputs when in the up position.
Switch 3 inserts 8 dB of attenuation to both the XLR and 1/4" T/R/S inputs when in the up position.