Check the listing for details. Rockford Fosgate PLC-U Universal Punch Level Control - Used, Open Box. Condition: Used. Listed at 39.99 USD. The PLC-U is designed as an inline, universal audio level control that can be integrated into almost any audio system. It is intended to allow you to vary the signal level of any stereo pair of RCA cables in the event you do not have a master volume control or you want more independent control over a specific signal path. The system is comprised of a high quality audio taper potentiometer which provides for true linear control of the output signal. It also comes with a variety of mounting configurations to meet your installation needs. A panel mount version which uses a 1" mounting hole and is held in place with a threaded retaining nut features a large and small knob option letting you choose which is best for the application.