The PC90 from LA Audio is a measuring system that allows for checking the polarity of any electronic audio signal path. For a system to perform correctly, the polarity of the signals must be maintained from input to output, otherwise severe signal degradation will occur. To that end, the system comprises two parts, an emitter and receiver, which can be placed at any point in an audio system.
The emitter produces a series of special pulses, which can be sent using either the built-in speaker, or by connecting the XLR output to a line or microphone input. The line output level can be adjusted using a front panel control knob. (The speaker level is fixed.) On receiving the signal, the receiver is able to determine whether the polarity is intact, and displays the result via green and red LEDs.
When using XLR connections, a selector switch on both the emitter and receiver allows the system to adapt for different wiring conventions, namely either pin-2 or pin-3 hot. The unit is powered via a 9V battery (not included).