The '4558' generic base number refers to a dual op amp (dual operational amplifier), currently sourced by Fairchild Semiconductor (KA4558 or MC4558), New Japan Radio Co., Ltd. ((NJM4558), ROHM Semiconductor (BA4558), STMicroelectronics (MC4558, TJM4558), and Texas Instruments (RC4558). The 4558 can be found in a wide variety of through-hole and surface-mount packages.