The -TPA1A modules are two pair audio amplifier modules compatible with RDL Format A twisted pair products. Each -TPA1A receives stereo audio and 24V DC power through a rear-panel RJ45 jack. The left and right audio signals received on pairs B and C of the twisted pair cable are summed to mono and amplified. The amplified output level is set by an internal VCA which is controlled by a front-panel volume control. The VCA attenuator provides years of scratch-free gain adjustment.