The RU-SH1 is used in applications requiring headphones of any impedance to be driven from consumer or professional audio sources. The module mounts in RACK-UP series rack mounts or in various RDL mounting accessories. The RU-SH1 is a dual channel headphone amplifier with balanced/unbalanced Left and right inputs. Each input accepts operating levels between -20 dBV and +20 dBu. Two recessed slide switches located on the top of the rear enclosure are set prior to mounting the module. One switch is provided for setting the input sensitivity. The mode switch selects between stereo and mono operation. In the mono position, the Left input is used to drive both output channels. When the module is used in a monaural system, only the Left channel input must be wired. The front panel level control is a long-life potentiometer controlling matched VCAs. Audio does not pass through this control, assuring years of noise-free level adjustment.